# Sound Decibel Meter — Full Documentation > Concatenated English source of every documentation page on https://sounddecibelmeter.org. Each section retains its original Markdown — including internal links (relative paths like `/calibration` resolve from the site root), tables, code blocks, and standard references. For the canonical version of any page, see https://sounddecibelmeter.org/. For the index pointer, see https://sounddecibelmeter.org/llms.txt. # How to Use the Sound Decibel Meter: Complete User Guide This guide walks through every feature of the [browser decibel meter](/) on this site — from a 30‑second first measurement to the advanced settings most users never touch. The meter runs entirely in your browser, requires no installation or account, and uses your device's microphone strictly for the duration of the session. By the end of this page you should know how to read the live display, choose the correct frequency and time weighting for your situation, calibrate your device for accuracy within a few decibels of a Class 2 reference meter, and trust the readings enough to base hearing decisions on them. If you only have a minute, jump to [Quick start](#quick-start). If you want the full picture, read straight through. ## Quick start 1. **Open the [home page](/) and click _Start_.** 2. **Allow microphone permission** when your browser prompts. The meter does not record or upload anything — see the [privacy section](#permission-and-privacy) below for the technical details. 3. **Read the live decibel value** at the center of the screen. The meter updates several times per second; the number you see is an A‑weighted, fast‑time‑weighted SPL value. That is all you need to take a first measurement. The rest of this page explains how to make that measurement more accurate, how to record sustained exposure, and how to interpret the readings against published health and regulatory thresholds. ## Permission and privacy The meter needs `getUserMedia` permission to read your microphone, and your browser will prompt you the first time you start it. There are two important properties of how this is implemented on our site: - **All audio processing happens locally** in the browser, in JavaScript and the Web Audio API. No PCM samples, no FFT frames, and no derived numbers are uploaded to any server. The site has no audio analytics endpoints because it has no server‑side audio handling at all. - **HTTPS is required.** Browsers refuse to grant microphone permission to pages served over plain HTTP. The site uses HTTPS by default and will redirect HTTP requests. You can revoke microphone access at any time by clicking the lock icon in your address bar (Chrome, Edge, Brave, Firefox), the camera icon (Safari), or by clearing site permissions in browser settings. Closing the tab releases the microphone immediately. If you are on a corporate network or a managed device that blocks `getUserMedia`, you will see "no microphone detected" — there is no workaround on our side; you'll need to use a personal device or ask IT for the policy exception. ## Reading the display The meter's main panel shows several distinct values at once. They look like one big number with some statistics below, but each carries different information. ### Current level (the big number) The large central reading is the **time‑weighted SPL at this instant**. "This instant" is qualified by the time weighting (Fast, 125 ms; Slow, 1 s; Impulse, 35 ms — see [Time weighting](#time-weighting) below) and the frequency weighting (A, C, or Z — see [Frequency weighting](#frequency-weighting)). The default settings are A‑weighted and Fast, which is the right combination for most environmental and occupational measurements. The number's color reflects the band it falls into. Green is comfortable, amber is loud‑but‑safe with limited exposure, red is hazardous. The color mapping uses the same boundaries as the [reference chart](#reference-chart) shown beneath the meter. ### Min, Avg, Max, Peak Below the current level, four smaller readings track the **session statistics** since you last clicked _Start_ (or _Reset_): - **Min** — the lowest valid reading observed. The meter waits a short startup window before starting to track Min, so the very first reading doesn't pin Min at the system noise floor. - **Avg** — the arithmetic average of all readings. Useful as a quick proxy for Leq when the noise is reasonably steady; for a true Leq measurement of variable noise, see the [tips page](/tips#multi-sample-averaging). - **Max** — the highest reading observed. With Fast time weighting this catches sustained loud events; with Impulse it catches transients (gunshots, hammer strikes, doors slamming). - **Peak** — the highest *unweighted* sample value, before time weighting. The meter holds the peak briefly so you can see brief transients that would otherwise vanish. The four colors update independently to reflect the band each value falls into — so Min might stay green while Peak is briefly red, telling you that the room is mostly quiet but had at least one loud event. ### Reference chart To the right of the live values is a vertical reference chart with bands from "threshold of hearing" up through "fireworks." A check mark next to a band indicates that your current reading falls inside that band. The band's color and example text help you sanity‑check the measurement: if the meter says 30 dB but your environment matches the description for 70 dB, your calibration is probably off (see [Calibration](#calibration)). ### Banner notification Above the chart, a contextual banner appears whenever your current reading lands in a meaningful band. It shows the matched range and a short health advisory ("Comfortable for normal activity," "Prolonged exposure may cause fatigue," etc.), with the dynamic values colored to match the band. ## Settings The settings panel (gear icon, top‑right of the meter) groups the parameters into four sections. Defaults are sensible for almost every use; the explanations below cover when to change them. ### Frequency weighting (A / C / Z) A‑weighting de‑emphasizes low frequencies in a way that approximates human hearing at moderate listening levels. It is the standard for occupational and environmental noise (OSHA, NIOSH, WHO, ISO 1996). Choose **A** unless you have a specific reason not to. C‑weighting is much flatter — it preserves low‑frequency content, which makes it the right choice for measuring concert sound, subwoofer output, and impulsive noise. If you are measuring a venue where the bass is the main concern, C‑weighting will give a higher and more representative number than A. Z‑weighting is unweighted (flat) — used for instrument verification and acoustic research. Most users will never need it. The math behind the weightings is on the [science page](/science#frequency-weightings). ### Time weighting (Fast / Slow / Impulse) Time weighting is an exponential averaging applied before the value is displayed: - **Fast (125 ms)** — the standard for most environmental and occupational measurements. Captures speech‑rate variation and short events without flickering. - **Slow (1 s)** — smoother readings for steady ambient noise. Useful when the source is roughly constant and you want a stable number to log. - **Impulse (35 ms)** — much faster response, designed to catch transients like gunshots, hammer strikes, and explosions. Reads noticeably higher than Fast for short events. When in doubt, use Fast. Switch to Impulse only when you specifically need to characterize transient events. ### Scale (dB SPL vs dB FS) dB SPL (sound pressure level) is the standard physical scale, calibrated to 20 µPa = 0 dB. This is the scale you want for any reading that should match published references — including the entire [comparison chart](/comparison). dB FS (full scale) is a digital‑audio scale where 0 dB FS corresponds to the maximum representable digital sample value. dB FS readings are useful for audio engineers comparing levels in a DAW but cannot be directly compared to physical SPL numbers without a reference calibration. Most users should leave the scale on dB SPL. ### Calibration offset A single number (in dB) added to every reading to compensate for your device's hardware bias. Phones and laptop microphones can be off by ±10 dB straight out of the box. The full procedure for setting this correctly is on the [calibration page](/calibration), but the short version is: pair our meter with a known reference (a Class 2 SLM, a calibrator at 94 dB SPL, or a quiet space at a known ambient level), average for 30 seconds, and enter the difference here. ### Update interval and peak hold The update interval controls how often the live number refreshes. The default of 200 ms (Fast) is a good compromise between responsiveness and visual stability; 50 ms (Realtime) is jumpy but precise; 1 s (Stable) smooths variable noise. Peak hold time controls how long a peak is displayed before it decays. Default is 3 seconds; Infinity holds the peak until you reset. ## Graph types Below the live values, a graph provides a temporal or spectral view of the signal. Four graph types are available: - **Line** — running time series of the level for the last several seconds. The line and the area beneath it are colored by the per‑sample band (green / amber / red), so you can see at a glance when exposure crossed thresholds. - **Bar** — a single live bar, colored by the current band. Cleanest view for at‑a‑glance reading. - **Visualizer** — a frequency‑domain bar chart (FFT spectrum), useful for identifying which frequency bands contribute most to the level. Bars are colored by intensity, low to high. - **Spectrum** — same FFT data as Visualizer but rendered as a line with a smooth gradient fill. Useful for spotting tonal components. The line graph is the right default. Switch to visualizer or spectrum when you need to know whether a measurement is dominated by low‑frequency mechanical hum, high‑frequency hiss, or a particular tonal source. ## Mobile vs desktop The meter behaves identically on iOS Safari, Android Chrome, and desktop Chromium / Firefox. A few practical differences: - **Microphone gain** varies dramatically across devices. A phone that reads 65 dBA in a quiet office may read 75 dBA on the next phone in the same room. This is not a bug; it is a hardware difference. Set the calibration offset per device. - **Battery saving and tab backgrounding** can throttle audio processing. iOS specifically suspends Web Audio when the tab is backgrounded for more than a few seconds. Keep the tab active for long measurements, or use the screen‑lock prevention some browsers offer for fullscreen mode. - **Bluetooth headsets** can confuse the input selector. If readings are oddly low or muffled, disconnect the headset and force the meter to use the built‑in microphone. For long unattended monitoring, a desktop with the laptop lid open is more reliable than a phone in standby. ## Troubleshooting ### "No microphone detected" on Start Causes, in order of likelihood: 1. Permission denied — click the lock icon next to the URL and reset microphone permission, then reload. 2. No microphone in the device — check that the system audio settings show an input device. 3. Browser policy on the page — uncommon, but some embedded browsers (in‑app webviews) block `getUserMedia` regardless of permission. 4. Hardware mute — many laptops have a physical mic kill switch. ### Reading stuck at 0 dB or extremely low Usually a hardware mute or a wrong input device. Check system sound settings for the active input. On laptops with multiple microphones, some browsers default to the wrong one. ### Wildly fluctuating readings Most often handling noise — the meter is picking up taps and rubbing on the device, not the room. Place the device on a stable surface, on a soft cloth if possible, with the microphone facing the source. Keep wind off the microphone (a foam pop filter or a parked location is enough). ### Numbers don't match a reference SLM Almost always calibration. Follow the [calibration procedure](/calibration) once per device and the readings should land within ±2 dB of a Class 2 meter for steady mid‑range sources. ## What to read next You have the full operating manual. To get the most from the meter: - Walk through the [calibration page](/calibration) once, on each device you use. - Skim the [measurement tips](/tips) for distance, weighting, and averaging best practices. - Use the [comparison chart](/comparison) to sanity‑check unfamiliar readings. - If you are responsible for an occupational program, see the [workplace standards page](/workplace) to know what level of evidence is required where. # Noise Level Comparison Chart: Sound Levels by Activity, Object, and Environment A **noise level comparison chart** turns raw decibel numbers into something intuitive: how loud is a vacuum cleaner versus a chainsaw? When does an environment cross the line from merely annoying to a measurable risk to your hearing? This page collects the reference levels published by [NIOSH](https://www.cdc.gov/niosh/topics/noise/), the [CDC](https://www.cdc.gov/nceh/hearing_loss/what_noises_cause_hearing_loss.html), and the [WHO](https://www.who.int/news-room/fact-sheets/detail/deafness-and-hearing-loss), arranges them in 10‑decibel bands from inaudible to immediately damaging, and explains how to read the numbers correctly. Use this chart together with our [live decibel meter](/) and the [calibration guide](/calibration) to get practical readings for the spaces you actually live and work in. ## How the decibel scale works A decibel (dB) is not a unit like a meter or a kilogram — it is a **logarithmic ratio** between two sound pressures. When the chart says a vacuum cleaner is "+30 dB louder than a quiet office," it means the pressure on your eardrum is roughly 32 times higher and the sound is perceived as about 8 times louder. Three properties of the scale matter when you read this chart: - **+10 dB ≈ 10× the sound intensity** but only **about 2× as loud** to a human listener. This is why a 90 dB lawn mower does not feel three times louder than a 30 dB whispered library — perception compresses the range. - **+3 dB doubles the acoustic energy.** Two identical machines running together produce 3 dB more than one alone. - **0 dB is not silence.** It is the [threshold of hearing](/glossary#threshold-of-hearing) for a healthy young ear at 1 kHz, defined as 20 µPa of pressure. Some anechoic chambers measure negative values. Most numbers on this page are reported as **dBA**, which is dB SPL passed through the [A‑weighting filter](/science#frequency-weightings) that approximates how a human ear responds at moderate listening levels. dBA is the weighting used by every major occupational and community noise standard. When a measurement is reported in **dBC** (low‑frequency rich content like concerts or thunder) or unweighted **dB SPL**, we mark it explicitly. ## The comparison chart at a glance The table below groups everyday sounds into 10‑decibel bands. The "safe daily exposure" column uses the [NIOSH Recommended Exposure Limit](/glossary#niosh-rel) (85 dBA per 8 h with a 3 dB exchange rate) — for every 3 dB above 85 dBA, the permissible exposure time is halved. | Band (dBA) | Examples | Subjective | NIOSH safe exposure | |---|---|---|---| | 0 – 10 | [Threshold of hearing](/glossary#threshold-of-hearing); anechoic chamber | Inaudible | Unlimited | | 10 – 20 | Pin drop, quiet breathing, falling snowflake | Just audible | Unlimited | | 20 – 30 | Soft whisper at 1 m, rural night, ticking watch | Very quiet | Unlimited | | 30 – 40 | Quiet bedroom, refrigerator hum, library reading room | Quiet | Unlimited | | 40 – 50 | Soft rain, residential evening, fan on low | Comfortable | Unlimited | | 50 – 60 | Quiet office, dishwasher in next room, average rainfall | Conversational | Unlimited | | 60 – 70 | Normal conversation at 1 m, air conditioner, sewing machine | Moderate | Unlimited | | 70 – 80 | Vacuum cleaner, busy traffic at 5 m, alarm clock, hair dryer | Loud | More than 25 h | | 80 – 85 | Heavy city traffic, food blender at 1 m, garbage disposal | Very loud | 16 – 25 h | | 85 – 90 | Subway train, lawn mower, motorcycle at 8 m, freight train | Risky with exposure | **8 h** | | 90 – 95 | Hand drill, food processor, bus horn, electric saw | Hazardous | 2 – 4 h | | 95 – 100 | Leaf blower, snowmobile, propeller plane cabin | Hazardous | 1 – 2 h | | 100 – 110 | Nightclub, helicopter at 30 m, pneumatic drill, chainsaw | Painful with exposure | 15 – 30 min | | 110 – 120 | Front row of a concert, ambulance siren at 3 m, race car cabin | Painful | 1 – 7 min | | 120 – 130 | Jet take‑off at 100 m, thunderclap nearby, jackhammer at 3 m | Pain threshold | Less than 1 min | | 130 – 140 | Air‑show ground level, jet engine at 30 m, fireworks at 5 m | Immediate damage | Not safe | | 140+ | Firearm at the shooter's ear, fighter jet at takeoff, balloon pop in ear | Immediate damage | Not safe | For ranges where listed examples cover more than one band (city traffic, for instance, ranges from 70 dBA on a quiet weekday to 85 dBA at peak rush hour), we list them in the band that matches typical mid‑day exposure. Real readings in your environment can vary by ±10 dB depending on distance, weighting, and calibration — see the [measurement tips](/tips) page for ways to reduce that variance. ## Detailed examples by environment The 10‑band table is the fast lookup. The sections below give context for the spaces where readers most often want a baseline: home, work, transit, entertainment, and outdoors. Numbers are typical mid‑range; quiet examples and peaks are noted where they materially change the safety picture. ### At home Most household sounds sit in the 30 – 70 dBA range, which is comfortable and poses no risk to hearing. The exceptions are kitchen appliances and power tools. - **Refrigerator (1 m)**: 40 – 45 dBA — usually below the WHO bedroom limit. - **Washing machine, dishwasher (running, 1 m)**: 55 – 70 dBA. - **Vacuum cleaner (canister at 1 m)**: 70 – 80 dBA. - **Food blender, hand mixer (lid off, 0.5 m)**: 85 – 95 dBA — over the hearing‑damage threshold for prolonged use. - **Hair dryer (high, near ear)**: 80 – 95 dBA — varies hugely by model. - **Plasma TV, normal listening volume (3 m)**: 50 – 70 dBA. - **Smoke alarm (1 m)**: 85 – 100 dBA — by design, briefly. If you are evaluating a [baby's bedroom](/use-cases#baby-and-children) or a [home office](/use-cases#home-office-and-remote-work), the WHO recommends a nighttime average of 30 dBA inside the bedroom and the [EPA](https://www.epa.gov/clean-air-act-overview/epa-history-noise-and-noise-control-act) recommends 45 dBA outdoors for residential areas. ### At work Office and retail spaces are usually 50 – 70 dBA. The risk picture changes sharply in industrial settings — construction sites, factories, and hospitality kitchens routinely cross the 85 dBA action level. The full [OSHA / NIOSH / EU breakdown is on the workplace page](/workplace), but as a quick reference: - **Quiet open‑plan office**: 50 – 60 dBA. - **Busy open‑plan office, call center**: 60 – 75 dBA. - **Restaurant kitchen at peak**: 75 – 90 dBA. - **Retail floor with music**: 70 – 85 dBA. - **Light manufacturing**: 80 – 95 dBA. - **Heavy manufacturing, metal stamping**: 95 – 115 dBA — eye and ear PPE required. - **Construction (general)**: 85 – 105 dBA. - **Construction (jackhammer at the operator)**: 100 – 120 dBA. In US workplaces, OSHA's permissible exposure limit (PEL) is 90 dBA over an 8‑hour shift; the action level for hearing‑conservation programs is 85 dBA. NIOSH recommends a stricter 85 dBA limit. The EU's Directive 2003/10/EC sets the upper exposure action value at 85 dBA and the absolute limit at 87 dBA. ### Transit and outdoors | Source | Typical (dBA) | Where measured | |---|---|---| | Quiet residential street | 40 – 50 | Pavement, no traffic | | Suburban traffic | 55 – 70 | 5 m from curb | | Urban arterial (rush hour) | 70 – 85 | Pedestrian level | | Bus, electric (cabin) | 65 – 75 | Rear bench | | Bus, diesel (cabin) | 75 – 88 | Rear bench | | Subway/metro train (platform) | 80 – 100 | Mid‑platform during arrival | | Subway/metro train (cabin) | 75 – 95 | Standing, accelerating | | Motorcycle (rider position) | 90 – 105 | Highway speed | | Car cabin (highway, ICE) | 65 – 80 | Driver seat | | Car cabin (highway, EV) | 60 – 72 | Driver seat | | Aircraft (cabin, cruise) | 75 – 88 | Mid‑cabin window seat | | Aircraft (apron, jet engines) | 110 – 140 | 50 m from engine | The [WHO Environmental Noise Guidelines for the European Region](https://www.who.int/europe/publications/i/item/9789289053563) recommend a community noise limit of 53 dB Lden (day‑evening‑night average) outdoors for road traffic and 45 dB Lnight for sleep protection. Most major cities exceed both. ### Entertainment, sport, and music This category is the most common cause of preventable hearing loss in adults because exposure is voluntary and rarely tracked. - **Movie theater, dialogue**: 65 – 75 dBA. - **Movie theater, action peaks**: 90 – 100 dBA. - **Sports stadium, average**: 80 – 100 dBA. - **Sports stadium, big play**: 100 – 120 dBA. - **Bar with live music**: 95 – 105 dBA. - **Nightclub dance floor**: 100 – 115 dBA. - **Rock concert (mid‑pit)**: 100 – 120 dBA. - **Personal headphones (max volume on phone)**: 95 – 110 dBA at the ear. - **In‑ear monitors (musicians)**: 100 – 115 dBA possible. A 100 dBA concert exceeds the NIOSH safe limit in 15 minutes. A 110 dBA show exceeds it in less than 2 minutes. This is the band where filtered earplugs (such as foam, musician's plugs, or the products linked from our [hearing health page](/health#hearing-protection)) make a measurable difference: a 20 dB‑rated earplug brings a 110 dBA front‑row exposure down to about 90 dBA, where the safe limit becomes 2 – 4 hours instead of 2 minutes. ## Reading the chart correctly The numbers above are useful only if you understand what they implicitly assume about distance, weighting, and time. ### Distance halves, level drops by 6 dB For a point source in free field, doubling the distance from the source reduces the SPL by approximately 6 dB. In practice — indoor spaces, reflective ground, multiple sources — the drop is closer to 3 – 5 dB per doubling. A jackhammer listed at "100 dBA at 3 m" is closer to 94 dBA at 6 m and 88 dBA at 12 m. This is the simplest noise‑control intervention available: increase distance. ### Weighting changes the number, not the sound A subwoofer playing 90 dB SPL at 50 Hz might read **90 dBC**, **76 dBA**, and **76 dB Z** (unweighted) on the same meter at the same instant. The A‑weighting filter de‑emphasizes low frequencies because the human ear is less sensitive there at moderate levels. Always check what weighting a published number uses before comparing it to your own readings — our [science page](/science#frequency-weightings) walks through the four standard weighting curves. ### Time integration matters for variable noise A single instantaneous reading of "90 dBA" does not tell you whether you can spend 8 hours there. NIOSH and OSHA limits are expressed as **time‑weighted averages (TWA)** — the equivalent‑energy level over a full work shift. A jet flyover that hits 110 dBA for 30 seconds does not blow your daily budget, but a constant 90 dBA loading dock does. The [tips page](/tips#time-weighting) covers when to use Fast, Slow, and Impulse time‑weightings, and when to switch to a Leq (equivalent continuous level) measurement. ## Health context: when the numbers cross the line The single most important threshold on this chart is **85 dBA** — the NIOSH exposure limit for an 8‑hour day. Below 85 dBA, indefinite exposure causes no measurable hearing damage in healthy adults. Above 85 dBA, the safe time shrinks rapidly: | Level (dBA) | NIOSH safe daily exposure | |---|---| | 85 | 8 hours | | 88 | 4 hours | | 91 | 2 hours | | 94 | 1 hour | | 97 | 30 minutes | | 100 | 15 minutes | | 103 | 7.5 minutes | | 106 | 3.75 minutes | | 109 | Under 2 minutes | | 112 | Under 1 minute | | 115 | Under 30 seconds | These limits assume **A‑weighted, time‑weighted exposure** and a 3 dB exchange rate (every 3 dB over 85 halves the safe time). OSHA's PEL uses a 5 dB exchange rate, which produces longer "safe" times that more recent research considers under‑protective. The hearing‑damage mechanism — mechanical fatigue of the cochlear hair cells — is non‑linear and cumulative; once a hair cell dies, mammalian cochleae do not regenerate it. The [hearing health page](/health) covers the biology, symptoms (tinnitus, threshold shift, speech‑in‑noise difficulty), and protection options in depth. ## Practical guidance Reading a comparison chart is one thing; acting on it is another. Three habits turn the numbers into actual protection: 1. **Measure the spaces you spend the most time in.** Your bedroom, your commute cabin, your gym. Most people overestimate how loud their environment is by 10 dB and underestimate the time they spend in it. 2. **Treat 85 dBA as a hard limit.** If a space reads above 85 dBA and you spend more than a few hours there, wear hearing protection or shorten the exposure. There is no medical benefit to "toughening up" — there is only damage and adaptation that hides it. 3. **Calibrate first, then trust your phone.** Consumer phones differ by ±10 dB straight out of the box; ours included. The [calibration guide](/calibration) walks through three methods that bring readings to within ±2 dB of a Class 2 reference meter — enough for personal exposure tracking. ## Frequently asked questions ### Is a 60 dB sound loud? 60 dBA is the level of normal conversation at one meter. It is comfortable for indefinite listening and well below any hearing‑damage threshold. It can still be too loud for sleep — the WHO recommends 30 dBA inside the bedroom — and it can interfere with focused work, where 50 dBA or lower is preferred. ### Why is a chainsaw 110 dB if a jet engine is 130 dB? Doesn't 20 dB feel like a small difference? On the decibel scale 20 dB is a 100‑fold increase in acoustic intensity and roughly a 4× increase in perceived loudness. The compressed feeling is real: your ear adapts to the dynamic range of normal life by trading off resolution at the loud end. That trade‑off is also why short, very loud exposures (a gunshot, a balloon pop, a fireworks shell at close range) cause damage that your subjective loudness perception does not warn you about. ### What's the loudest sound a person can survive? Sustained exposure above 140 dB SPL causes immediate physical damage to the ear (tympanic membrane rupture, hair‑cell death). Brief impulses up to about 180 – 200 dB are survivable but cause permanent hearing loss; above that range the sound becomes a shock wave and starts damaging soft tissue beyond the ear. The reference cases are firearms (155 – 175 dB at the shooter's ear) and explosive blasts. ### Can I measure 130 dB with a phone? Most phone microphones clip between 95 and 110 dB SPL because they are designed for voice calls, not for sound‑level measurement. Above the clipping point, the meter under‑reports the level. For anything above ~100 dBA you need a Class 2 sound‑level meter (IEC 61672) or a dedicated dosimeter. Our browser meter is intended as a screening tool below the clipping range; the [FAQ](/faq) explains the limits in more detail. ## How we sourced these numbers The reference levels above come from: - [NIOSH Sound Level Meter App documentation](https://www.cdc.gov/niosh/topics/noise/) — mid‑range values for occupational sources. - [CDC "What noises cause hearing loss?"](https://www.cdc.gov/nceh/hearing_loss/what_noises_cause_hearing_loss.html) — household and personal listening levels. - [WHO Environmental Noise Guidelines for the European Region (2018)](https://www.who.int/europe/publications/i/item/9789289053563) — community and night‑time levels. - [EPA "EPA Identifies Noise Levels Affecting Health and Welfare" (1974, still cited)](https://www.epa.gov/clean-air-act-overview/epa-history-noise-and-noise-control-act). - ISO 1996‑1 / 1996‑2 (acoustic terminology and outdoor noise measurement). The "subjective" column is qualitative — it summarizes how listeners typically describe the band, not a perceptual measurement. Real‑world levels vary with distance, room acoustics, source condition, microphone, and weighting; treat this chart as a calibrated starting point, not a guarantee. --- Want to compare these numbers to your own environment? Open the [live decibel meter](/) on this site, calibrate it once with the [calibration guide](/calibration), and start logging the spaces that matter to you. # How to Calibrate a Decibel Meter on Your Phone or Laptop A consumer phone or laptop microphone, used straight from the factory, can report sound levels that are off by **5 to 15 dB** from a calibrated Class 2 sound‑level meter. That is not a defect — it is the unavoidable consequence of using a device that was engineered for voice calls and ambient noise suppression as if it were a measurement instrument. The good news is that calibrating away most of this error is a 5‑minute job, requires no special equipment, and brings the [browser meter](/) on this site into agreement with a reference within ±2 dB for typical environmental and occupational ranges. This page covers three calibration methods (in order of accuracy and practicality), explains how to set the calibration offset in our settings panel, and is honest about the limits of what consumer hardware can do. ## Why calibration matters The decibel scale is calibrated to a fixed physical reference: 0 dB SPL = **20 micropascals (µPa)** of pressure variation. A correctly calibrated sound‑level meter, given a 94 dB SPL reference signal, reads exactly 94 dB. Anything less is a measurement bias — a constant offset between the level of the actual sound and the number on the screen. Three sources of bias dominate consumer hardware: - **Microphone sensitivity tolerances.** MEMS microphones in phones and laptops are typically specified at −38 dBV/Pa ± 3 dB. That ±3 dB spread translates directly into ±3 dB of measurement bias before any other factor. - **Pre‑amp gain and ADC scaling.** The signal chain from the microphone through the analog front end to the digital sample value adds a few decibels of variability and is not standardized across devices. - **Audio pipeline processing.** Most modern operating systems and browsers apply automatic gain control (AGC), echo cancellation, noise suppression, and equalization to microphone input. Each of these changes the relationship between the room SPL and the digital sample value, often non‑linearly with level. The browser meter on this site already requests the microphone with processing disabled where the platform supports it (`echoCancellation: false, noiseSuppression: false, autoGainControl: false` in the `getUserMedia` constraints). Even so, residual platform processing and microphone tolerances mean every device benefits from a one‑time calibration. ## Method 1 — Reference SLM cross‑check (the practical default) If you have access to a calibrated Class 2 sound‑level meter (yours, a co‑worker's, an EHS department's), this is the easiest and most reliable calibration. It captures the offset under a realistic room signal and takes about five minutes. 1. **Place both meters together.** Set your phone or laptop running our meter side‑by‑side with the reference SLM, microphones at the same height and orientation, ideally within 5 cm of each other. 2. **Pick a steady source at moderate level.** A constant white‑noise source at 60 – 80 dB is ideal — running fan, ventilation duct, dial tone on speakerphone. Avoid music with loud transients and avoid the quietest environments where the noise floor of either meter dominates. 3. **Configure both for matching settings.** A‑weighted, Slow time weighting on both. Slow averages out short fluctuations that would otherwise make the comparison noisy. 4. **Average for 30 – 60 seconds.** Watch both readings. Most reference SLMs show a running Leq; for our meter, watch the Avg statistic. 5. **Compute the offset.** Reference reading minus our reading, in dB. If the reference reads 70 dBA and ours reads 65 dBA, the offset is **+5 dB**. 6. **Enter the offset in settings.** Open the gear menu, scroll to "Calibration offset," enter the computed value (signed). Hit save. A second 30‑second comparison after entering the offset should show the two meters within 1 dB of each other. If they differ by more than 2 dB on a steady source, your device's frequency response is non‑flat at the test source's spectrum — try a broadband source like a fan or HVAC duct, not a tonal source like a TV. ## Method 2 — Acoustic calibrator (the gold standard) Industrial hygienists and acoustic researchers calibrate with a **pistonphone** or **acoustic calibrator** — a device that fits over the microphone and produces a precise reference tone, typically 94 dB SPL or 114 dB SPL at 1 kHz, traceable to national metrology standards ([IEC 60942](https://www.iec.ch/) Class 1 or Class 2). If you have access to one (e.g., from an EHS or audio engineering team): 1. **Fit the calibrator over the microphone.** This is the awkward step on a phone or laptop, because most consumer mic ports are too small, recessed, or off‑axis for the calibrator coupler. A small piece of adapter foam or tape can help, but the seal will not be perfect. 2. **Activate the calibrator (94 dB SPL, 1 kHz).** Run our meter for 30 seconds with A‑weighting, Fast. 3. **Compute the offset.** 94 minus our reading. Enter in settings. The calibrator method is the most accurate by design — but consumer microphone form factors limit how reliably you can couple the calibrator to the actual microphone diaphragm. For most users, Method 1 (reference SLM in the same room) gives indistinguishable results with much less hassle. ## Method 3 — Quiet‑baseline (last resort) If you have neither a reference SLM nor a calibrator, you can anchor the meter against a known quiet level. This is the least accurate of the three methods but takes nothing more than your device and a quiet room. 1. **Find a known quiet space.** A quiet bedroom at night is typically 30 – 35 dBA; a sound‑treated home studio can be 25 dBA; a library reading room is usually 35 – 40 dBA. 2. **Wait until the room is steady.** Stop walking, hold the device still, ask anyone present to be quiet. Run our meter with Slow time weighting, A‑weighting, for 60 seconds. 3. **Compare to the expected value.** A typical quiet bedroom reads 30 – 35 dBA on a calibrated meter. If your meter reads 25 dBA in a space you'd describe as "quiet bedroom," your offset is approximately +5 to +8 dB. Conversely, if it reads 50 dBA, your device is over‑reading by 15 to 20 dB and the calibration offset is negative. This method is rough — it assumes you correctly classify the room acoustically — but for someone with no reference equipment, it gets the calibration into the right ballpark and prevents readings from being silly. It is much better than no calibration at all. ## Setting the calibration offset Once you have a number, enter it in the meter: 1. Click the **gear icon** (top‑right of the meter). 2. Find the **Calibration offset** field. 3. Enter the offset, including the sign. Examples: `+5` if your meter reads 5 dB lower than the reference; `-3` if it reads 3 dB higher. 4. Save. The offset persists in your browser's local storage for that origin and device, so it is remembered across sessions. It does **not** sync across devices — phones and laptops typically need different offsets, and even two phones of the same model can differ by a few decibels. If you want to test multiple devices, store each device's offset separately. We have a roadmap item to add named per‑device profiles; for now you'll need to remember each device's number. ## When to recalibrate A few situations warrant re‑running the calibration: - **New device or new browser.** The audio pipeline differs across Chrome / Firefox / Safari and across OS versions. Re‑calibrate after a major OS update if readings drift. - **New microphone.** External USB or Bluetooth microphones have their own calibration. Bluetooth in particular is tricky because the encoded codec changes the perceived level non‑linearly. - **Significant temperature or humidity change.** MEMS microphones drift with environment, but the effect is small (sub‑decibel) for typical indoor conditions. - **Disagreement with a known reference.** If a measurement disagrees with a published reference by more than 5 dB on a steady source, recalibrate before treating the disagreement as real. A monthly check against the same reference space (same fan in the same room) is a good habit if you use the meter for any decision that matters. ## What you cannot calibrate around Three limitations of consumer microphones are not fixable by setting a calibration offset. ### Maximum SPL clipping Most phone and laptop microphones clip — that is, their analog front end saturates and the digital signal is no longer proportional to the input — somewhere between **95 and 110 dB SPL**. Above the clipping point, the meter under‑reports the actual level. There is no offset that fixes this; the information is gone before the meter ever sees it. If you need to measure 100 dBA or louder reliably, you need a Class 2 sound‑level meter (IEC 61672‑1) or a dedicated dosimeter. Our browser meter is an excellent screening tool **below** the clipping range. ### Frequency response A perfect measurement microphone has a flat frequency response from 20 Hz to 20 kHz. Phone and laptop mics have peaks and dips of several decibels across that range — engineered for voice (200 Hz – 4 kHz) at the expense of low‑frequency rumble and high‑frequency air. The calibration offset is a single scalar; it cannot correct a non‑flat frequency response. In practice this means our meter will be quite accurate on broadband mid‑range sources (traffic, conversation, HVAC) and somewhat less accurate on heavily low‑frequency or high‑frequency sources. C‑weighting amplifies low‑frequency error; A‑weighting suppresses it. When in doubt, A‑weight. ### Time integration The meter reads time‑weighted instantaneous values; calibration of a single value at a steady level does not guarantee accurate Leq integration over an hour, especially with variable noise. The [tips page](/tips#time-weighting) covers when this matters. ## Verifying the calibration After setting the offset, do one repeatability check: 1. **Take three 30‑second readings** of a steady source (same fan, same distance). Each should land within 1 dB of the others. 2. **If readings drift more than 1 dB**, the source isn't actually steady or your device's AGC is still active despite the `getUserMedia` flags. Try a different source (an HVAC duct from 1 m is usually the most reliable). 3. **Cross‑check with a different reference** if you have one. If two independent references agree within 2 dB, your calibration is trustworthy. A calibrated browser meter, used within its limitations, is good enough for almost everything except formal compliance documentation. The [guide](/guide), [tips](/tips), and [comparison chart](/comparison) all assume you've done this once — without calibration, every reading on this site is off by an unknown but probably non‑trivial amount. # Sound Measurement Tips: How to Get Accurate Decibel Readings A sound‑level meter only reports what it captures at the microphone. The quality of the captured signal depends on **where you place the meter**, **which weighting and time response you choose**, **how you handle the device**, and **how you average the result**. Get those right and a calibrated phone meter agrees with a Class 2 reference to within ±2 dB on typical environmental sources. Get them wrong and the same phone gives you readings that are off by 10 dB or more — not because the meter is bad, but because the measurement was wrong. This page collects the practical techniques that move readings from "rough estimate" to "trustworthy." It assumes you have already done the [calibration procedure](/calibration) once for the device. None of these tips compensate for an uncalibrated meter — they extract reliable numbers from a calibrated one. ## Microphone placement The microphone is the only thing that "hears" the room. The closer it is to the source, the more reflective surfaces it sees, and the more turbulent the air around it, the more those factors dominate the reading over the actual sound you care about. ### Distance from the source For an idealized point source in free field, the **inverse‑square law** predicts that doubling the distance reduces the SPL by 6 dB. Real indoor measurements rarely match that perfectly because of room reflections, but the trend holds: | Distance from source | Drop from reference (dB) | |---|---| | 1 m | 0 (reference) | | 2 m | −6 | | 4 m | −12 | | 8 m | −18 | | 16 m | −24 | For occupational measurements, the rule is **measure where the worker's ear is**. For environmental measurements, choose the location that matters: bed pillow level for sleep noise, working surface for office noise, dance floor center for venue measurements. If you are publishing a number, always note the distance. "Lawn mower: 85 dBA at 5 m" is a complete statement; "lawn mower: 85 dBA" is ambiguous and roughly useless to someone trying to estimate the level at a different distance. ### Free field vs reflective field A perfectly free field has no reflective surfaces. An anechoic chamber approximates one; an open meadow on a windless day is the next best thing. Most rooms are highly reflective, especially small hard‑surfaced rooms like bathrooms, kitchens, and elevator cabs. In a reflective room, the SPL at most points is dominated by the **reverberant field**, not the direct sound from the source. This has two practical consequences: - The direct‑field 6 dB‑per‑doubling rule breaks down a few meters from the source. - The reading at one position can shift by 3 – 6 dB if you move the mic 0.5 m, because of standing‑wave nulls and antinodes. To suppress this, average over multiple positions in the room (at least three, separated by ~1 m), and report the mean. ### Avoid handling, pockets, and surfaces The microphone in your phone or laptop picks up vibration as easily as it picks up airborne sound. Holding the device in your hand introduces finger noise and clothing rustle that can add 5 – 15 dB at low frequencies. Setting the device on a hard table introduces ground reflection. Practical placement that works on every device: - Set the device on a folded soft cloth (a microfiber cloth, a t‑shirt) on a table at chest height. - Orient the microphone toward the source. Most phones have the mic at the bottom edge, but it varies — verify with a clap test if unsure. - Once the device is placed, **don't touch it** during the measurement. For very long measurements, a small tripod with a smartphone clamp holds the device free of any surface and provides the cleanest reading. ## Frequency weighting The meter applies a frequency weighting before computing the SPL. Three choices are commonly used; they give very different numbers for the same sound. | Weighting | When to use | Typical effect | |---|---|---| | **A** | Occupational noise, environmental noise, anything compared to public‑health thresholds | Reads lower than C on bass‑rich sources (suppresses lows) | | **C** | Concerts, subwoofers, impulses, thunder, fireworks | Reads higher than A when bass dominates | | **Z** | Research, instrument verification | Truly flat, rarely needed for field measurements | The default for almost every published reference (NIOSH REL, OSHA PEL, WHO community guidelines, ISO 1996) is A‑weighting. Unless you have a specific reason — usually because the source is dominated by frequencies below 200 Hz — leave the meter on **A**. If you are measuring a venue with significant subwoofer content and your A‑weighted reading seems too low for what you can feel in your chest, switch to C and report both. The difference between A and C is itself diagnostic: a 20 dB gap (C is 20 dB higher) means the source is dominated by bass; a 5 dB gap means it is mid‑frequency. The full math behind the weighting curves is on the [science page](/science#frequency-weightings). ## Time weighting Time weighting is an exponential averaging applied before the value is displayed. Three settings are standard: - **Fast (125 ms time constant)** — captures speech‑rate variation and short events without flickering. The default for nearly everything. - **Slow (1 s time constant)** — smoother readings for steady ambient noise. Use when you want a stable number to log and the source is steady. - **Impulse (35 ms attack, 1.5 s decay)** — designed to catch transients (gunshots, hammer strikes, balloon pops). Reads markedly higher than Fast for short events. A common mistake is leaving the meter on Slow when measuring an intermittent or impulsive source. Slow underreports peaks because the 1‑second time constant doesn't have time to "settle" to the peak before the event passes. Use Fast unless you specifically want the smoothing. For sources with frequent strong transients — workshop tools, sporting events, rifle ranges — Impulse is the most representative weighting, and it is the one some standards (ISO 9612 for occupational measurements with prominent impulses) require. ## Multi‑sample averaging A single 5‑second reading captures only the noise during those 5 seconds. For variable sources, that snapshot is rarely representative of the longer‑term exposure that matters for health. Two averaging strategies cover most cases: ### Arithmetic mean (Avg) The Avg statistic on our meter is the arithmetic mean of all displayed values. For approximately steady noise, this is a fine estimate of the ambient level — for example, a fan running at 55 dBA continuously will have Min, Avg, and Max all within 2 dB of each other. ### Equivalent continuous level (Leq) For variable noise, the appropriate quantity is the **equivalent continuous A‑weighted level**, or **LAeq**. This is the steady SPL that would deliver the same total acoustic energy over the measurement period as the actual variable signal. Mathematically: ``` LAeq,T = 10 × log10( (1/T) × integral( 10^(LA(t)/10) ) dt ) ``` The browser meter does not compute Leq directly today, but for reasonably steady or non‑extreme noise, the Avg statistic is within 1 dB of LAeq. If you are publishing a number that needs the energy‑equivalent definition (e.g., for a noise‑complaint measurement), use a Class 2 SLM with built‑in Leq integration. ### How long to measure | Source type | Minimum duration | |---|---| | Steady ambient (fan, HVAC) | 30 seconds | | Office, restaurant, retail | 5 minutes | | Traffic noise (suburban) | 10 minutes | | Traffic noise (urban arterial) | 1 hour | | Construction site, factory | 1 hour over the typical work cycle | | Concert, club, sports event | full event duration | Shorter samples on variable sources risk catching atypical conditions — either a quiet pocket or a peak event — and reporting them as representative. ## Eliminating contamination Most large measurement errors come from things that are not the source you intended to measure. Identify and eliminate them in this order: 1. **Wind on the microphone.** Even a light breeze creates pressure fluctuations that read as 60 – 80 dBA at the mic. Outdoor measurements without a windscreen are unreliable above ~1 m/s of wind. A foam ball over the mic helps; for serious outdoor work, use a furry ("dead cat") windshield. 2. **Handling and cable noise.** Discussed above. Set the device down on cloth and don't touch it. 3. **HVAC, fridge, computer fan in the same room.** Background noise below 10 dB lower than the target is fine to ignore. Background between 10 and 6 dB lower than the target requires a correction (subtract about 1 – 2 dB from the combined reading). Background less than 6 dB lower than the target makes the measurement unreliable — either eliminate the background or use a different location. 4. **Operator presence.** Your breathing, clothing rustle, and footsteps are surprisingly loud at close range. Stand back from the meter; if you have to be near it, freeze. 5. **Rain on the device.** Even fine drizzle taps the device with audible energy. Use a covered location for outdoor measurements. ## Specific scenarios A few common situations have their own quirks worth knowing. ### Outdoor traffic monitoring ISO 1996‑2 requires measurement at 7.5 m from the road centerline, at 1.2 m height, with a windscreen. For informal home use, choose a position close to the receiver of interest (the bedroom window, the patio chair) and average for at least 10 minutes during representative traffic conditions. ### Workplace machinery Measure where the operator's ear is during normal use. If the operator moves between positions, take the time‑weighted average across positions weighted by the time spent at each. For variable‑duty equipment (intermittent stamping presses), measure across at least one full cycle. ### Concerts, clubs, and venue volumes C‑weighting reads more representatively than A‑weighting because the sound is bass‑heavy. Measure at multiple positions (front, middle, back, sides) — venue sound is rarely uniform. The [hearing health page](/health) has guidance on what protector NRR you need for different exposure durations. ### Baby room overnight Use Slow time weighting and average over at least one full hour during the time of night you care about. The WHO bedroom recommendation of 30 dBA LAeq during sleep is the reference. White‑noise machines, if used, should produce **no more than 50 dBA at the crib position** — many machines on max volume far exceed that. ### Restaurant or office acoustics Measure during peak occupancy. Empty rooms read 10 – 20 dB quieter than full rooms. The published "comfort" thresholds (50 dBA office, 70 dBA restaurant) apply to the in‑use condition. ## Limitations of phone measurements A calibrated phone meter is a screening tool. It is excellent for mapping spaces, identifying problem areas, and giving non‑specialist users visibility into their own exposure. It is not a Class 2 sound‑level meter, and a few situations require one: - **Compliance documentation.** OSHA inspections, workers' compensation claims, formal noise‑complaint cases all require a calibrated SLM (and usually a calibrator, paperwork, and a chain of custody for the readings). - **Levels above ~95 dBA.** Most phone microphones clip in this range, under‑reporting the actual level. A Class 2 SLM is rated to ≥130 dB. - **Frequency analysis.** Our meter shows a real‑time FFT that is useful for diagnosis but is not a 1/3‑octave or octave‑band analyzer. Standards that specify octave‑band measurements need dedicated equipment. For everything else, a calibrated phone, careful placement, and the right weighting and time response will produce numbers you can trust. ## Pulling it together A reliable measurement is the result of all of the above being right at the same time. As a checklist for any measurement that matters: - [ ] Calibrated this device against a known reference ([procedure](/calibration)) - [ ] Microphone placed at the listener's position, on a soft surface, not handled during the read - [ ] A‑weighting (or C‑weighting if specifically measuring bass) - [ ] Fast time weighting (or Impulse for transient sources) - [ ] Wind and handling controlled (windscreen if outdoor, hands off the device) - [ ] Background noise at least 6 dB below the target, ideally 10 dB - [ ] Averaged over a duration appropriate to the source (at least 30 s for steady, 10+ min for variable) - [ ] Source distance and weighting reported alongside the number Done well, this gives a reading that is both accurate and reproducible — two qualities you will want every time the number you report has consequences. # Noise and Your Hearing: How Loud Is Too Loud, and Why It Matters **Noise-induced hearing loss (NIHL)** is the second most common form of sensorineural hearing loss after age‑related decline, and it is almost entirely preventable. The damage threshold is well established: prolonged exposure above **85 dBA** progressively kills the sensory hair cells in your inner ear, and unlike most cells in your body, those hair cells do not grow back. This page explains the biology, the regulatory thresholds, and the practical hearing‑protection options — drawing on the [NIOSH](https://www.cdc.gov/niosh/topics/noise/), [CDC](https://www.cdc.gov/nceh/hearing_loss/), and [WHO](https://www.who.int/news-room/fact-sheets/detail/deafness-and-hearing-loss) research that defines current best practice. If you are looking up this topic because something in your life sounds louder than it should — your gym class, your commute, a new appliance, a teenager's headphones — the practical answer is simple. Measure it, and if the reading is above 85 dBA for sustained periods, intervene now. Hearing damage is cumulative, irreversible, and quiet until it is not. ## The 85 dBA threshold, and why two agencies disagree on it The single most cited number in hearing science is **85 dBA over an 8‑hour day** — the [NIOSH Recommended Exposure Limit (REL)](https://www.cdc.gov/niosh/docs/98-126/). NIOSH derived this limit from large workplace cohort studies: at 85 dBA over a 40‑year career, an estimated 8 % of exposed workers develop measurable hearing loss. The agency considers this the lowest level at which long‑term exposure begins to produce a statistically meaningful risk above the natural age‑related decline. OSHA — the regulatory enforcement arm — uses a different number: **90 dBA over 8 hours**, with hearing‑conservation programs triggered at the 85 dBA action level. The OSHA standard also uses a 5 dB exchange rate (every 5 dB above 90 halves the safe time), while NIOSH uses a 3 dB exchange rate (the energy‑equivalent rule that physics actually supports). The result is that OSHA's PEL is roughly four times more permissive than the NIOSH REL at high levels. Why the gap? OSHA's standard has not been substantively updated since 1983, and changing it requires a federal rulemaking process. NIOSH publishes recommendations based on current science. Most modern occupational health practitioners — and every comparable European and Australian standard — follow the 85 dBA / 3 dB approach. We use NIOSH numbers throughout this site, but cite OSHA where it is the legally enforceable floor. For people not covered by occupational regulations — concertgoers, gym members, motorcycle riders, parents in noisy homes — the threshold is the same. **Above 85 dBA, exposure time is what saves you, and it gets short fast.** ## How sound damages the ear The ear is a precision organ tuned to detect pressure changes as small as a few billionths of an atmosphere. The damage mechanism for loud sound is unfortunately also mechanical, which means there is no pharmacological way to prevent or undo it. ### Anatomy in 60 seconds Sound enters as pressure waves, hits the eardrum, and is transferred through three tiny bones (malleus, incus, stapes) into the **cochlea** — a fluid‑filled spiral about the size of a pea. Inside the cochlea, the **basilar membrane** runs the length of the spiral and is tuned so that high frequencies vibrate the base and low frequencies vibrate the apex. Sitting on the basilar membrane are roughly **15,000 sensory hair cells** in two rows: outer hair cells that mechanically amplify the basilar membrane motion (giving the ear its incredible 120 dB dynamic range), and inner hair cells that translate that motion into neural signals. The hair cells get their name from the **stereocilia bundles** on top — tiny hair‑like structures that bend in response to fluid motion. Sustained exposure to loud sound damages those bundles in two ways: short‑term metabolic exhaustion (a temporary threshold shift, or TTS, that resolves over minutes to days) and longer‑term mechanical disruption that kills the cells outright (a permanent threshold shift, or PTS). ### Why the damage doesn't reverse Mammalian cochlear hair cells **do not regenerate** in adulthood. Birds, fish, and amphibians can regrow theirs; humans, mice, and dogs cannot. As of 2026, several research groups have published encouraging data on hair‑cell regeneration via gene therapy ([Frequency Therapeutics, Decibel Therapeutics, the Hudspeth lab at Rockefeller](https://www.nidcd.nih.gov/)), but no treatment has cleared full Phase III trials. For all practical purposes, the hair cells you have today are the only ones you will ever have. This is the asymmetry that makes hearing loss so insidious. Most people lose hair cells gradually over decades, and the loss begins in the high‑frequency region (the base of the cochlea), which is exactly the region the brain uses to distinguish consonants in speech. By the time you notice you have trouble following conversations in noisy rooms, the underlying damage is already substantial and not recoverable. ## Symptoms and signs Early NIHL is silent. The classic warning signs are: - **Tinnitus** — ringing, buzzing, or whining in the ears, sometimes only after loud exposure (a temporary tinnitus after a concert is the cochlea protesting; chronic tinnitus often follows). The CDC estimates 50 million Americans live with tinnitus. - **Difficulty in noise** — you can hear someone in a quiet room but can't follow them in a restaurant. This is the cocktail‑party problem, and it shows up before pure‑tone audiograms catch the loss. - **Muffled high frequencies** — birds, doorbells, women's and children's voices sound less crisp than they used to. - **Audiogram notch at 4 kHz** — the classic NIHL signature on a clinical hearing test, even when other frequencies still test normal. - **Hyperacusis or recruitment** — sounds become uncomfortably loud at lower thresholds, a sign that the remaining hair cells are over‑amplifying to compensate. If you experience persistent tinnitus, sudden hearing loss in one ear, or a notable change in your ability to follow speech in noise, see an audiologist. A baseline audiogram is also reasonable for anyone over 40 or anyone with regular high‑exposure activities (live music, motor sports, firearms, construction). ## Exposure time chart (NIOSH) This is the table that turns "is 90 dB loud?" into a concrete daily budget. Each row is the maximum daily exposure NIOSH considers safe at that level, A‑weighted, time‑weighted, with a 3 dB exchange rate. | Level (dBA) | Safe daily exposure | |---|---| | 80 | 24 hours | | 82 | 16 hours | | 85 | **8 hours** | | 88 | 4 hours | | 91 | 2 hours | | 94 | 1 hour | | 97 | 30 minutes | | 100 | 15 minutes | | 103 | 7.5 minutes | | 106 | 3.75 minutes | | 109 | Under 2 minutes | | 112 | Under 1 minute | | 115 | Under 30 seconds | | 118 | Under 15 seconds | A worked example. You ride a motorcycle to work (95 dBA at the rider's ear, 30 minutes each way) and lift weights at a gym with loud music (90 dBA, 60 minutes). The motorcycle leg is **30 min × 2 = 1 h at 95 dBA** — the daily budget at 95 is roughly 45 min, so commuting alone consumes ~133 % of the safe daily dose. The gym session at 90 dBA adds another 60 % of its own daily budget. These doses sum (with appropriate energy weighting), and you are already in a hearing‑damaging schedule before you have even gone to the weekend concert. The point of the table is not to scare you out of activities you enjoy. It is to make the trade‑offs visible: if you wear a 20 dB‑rated earplug at the gym, the exposure drops from 90 dBA to 70 dBA, the daily budget becomes effectively unlimited, and you preserve hours of remaining quota for the rest of your life. ## Personal headphones and earbuds Direct‑to‑ear listening is the most common modern source of NIHL outside occupational contexts. Modern phones, when set to maximum volume into wired or sealed in‑ear headphones, can deliver **95 to 115 dBA** at the eardrum. A teenager listening at 100 % volume for two hours a day is using their entire NIOSH budget on entertainment, with nothing left for the rest of life. The [WHO Make Listening Safe initiative](https://www.who.int/initiatives/make-listening-safe) recommends: - **The 60 / 60 rule** — no more than 60 % of maximum volume, for no more than 60 minutes a day. (This is a heuristic — the actual safe duration depends on the headphone and the source level.) - **Use built‑in volume monitoring.** iOS Health and Android Digital Wellbeing both estimate cumulative weekly exposure if you let them. - **Prefer over‑ear or active noise‑cancelling headphones.** When ambient noise drops, you naturally turn the music down, which is the largest practical gain. - **Take quiet breaks.** Hair cells recover from temporary threshold shifts during silence; chronic exposure with no recovery is worse than the same cumulative dose with quiet pauses. ## Children and infants Children are not just small adults when it comes to hearing risk. The infant ear canal is shorter, which raises resonance and amplifies high frequencies; infants and toddlers also have less ability to move themselves out of noisy environments or to communicate discomfort. The [WHO recommends](https://www.who.int/europe/publications/i/item/9789289053563) a maximum bedroom level of **30 dBA LAeq** during sleep for children, and [ASTM F963](https://www.astm.org/standards/f963) limits children's toy sound output to 85 dBA at 25 cm from the user's ear (with a 65 dBA limit on toys held close to the ear). For new parents, the practical implications are: - White‑noise machines should be set so the level **at the crib** is no higher than ~50 dBA. Many machines on max volume, placed less than a meter from a baby's head, exceed 85 dBA — the opposite of soothing. - Concerts, fireworks, and motorsport events with infants present require child‑sized hearing protection (foam earplugs do not fit, but infant‑sized ear muffs do). - Schools should meet [ANSI S12.60](https://webstore.ansi.org/standards/asa/ansiasa1260201) — 35 dBA background, 0.6 s reverberation — to support speech intelligibility during learning. Most do not, particularly noisy cafeterias and gymnasiums. ## Long‑term consequences beyond hearing Loud noise affects more than the ear. Decades of research from the [European Heart Journal](https://academic.oup.com/eurheartj) and the WHO's [Burden of Disease from Environmental Noise (2011)](https://www.who.int/europe/publications/i/item/9789289002295) report show measurable links between chronic noise exposure and: - **Cardiovascular disease** — sustained noise above ~55 dB at the bedroom window correlates with elevated risk of hypertension and ischemic heart disease, mediated by stress hormones and disrupted sleep. - **Sleep disruption** — even when you don't consciously wake, traffic peaks above 45 dB inside the bedroom shift sleep architecture and reduce restorative deep sleep. The WHO night noise guideline of 40 dB Lnight outside the bedroom is set at this threshold. - **Cognitive performance** — children growing up under flight paths or near major roads show measurably lower reading scores on standardized tests, even when controlled for socioeconomic factors. - **Mental health** — chronic noise exposure correlates with increased rates of anxiety and depression in cross‑sectional studies, though causation is harder to establish. These are population‑scale effects, not individual diagnoses. But they argue for treating environmental noise as a public‑health issue on par with air quality. ## How to protect your hearing Hearing protection works on three principles, in order of effectiveness: **eliminate the source**, **increase the distance**, **reduce the time**. Wearing a plug or muff is the last line of defense, not the first — but it is also the most accessible. ### Earplugs - **Foam plugs** (3M E‑A‑R Classic, Howard Leight Max) — NRR 29 – 33 dB. Cheap, disposable, very effective if rolled and inserted correctly. Most users insert them too shallowly and get half the rated attenuation. - **Filtered "musician's" plugs** (Loop Experience 2, Eargasm, Etymotic ER‑20) — NRR 16 – 23 dB with a flatter frequency response. Music sounds like music, conversation remains intelligible, and the protection is enough for concerts, clubs, and motorcycles. The most common honest recommendation for non‑occupational use. - **Custom molded plugs** (audiologist‑fitted) — best long‑term option for musicians and people with frequent high exposure. NRR 15 – 25 dB depending on filter, and they actually stay in. ### Earmuffs - **Passive muffs** (3M Peltor X5A) — NRR up to 31 dB. Awkward in summer and over glasses, but unmatched for impulse noise (firearms, hammering). - **Electronic muffs** (3M Peltor SportTac, Walker's Razor) — pass through conversation and warning sounds, clamp down on impulses. Worth the premium for shooters and machine operators. - **Active noise cancelling headphones** (Bose QC, Sony WH‑1000XM) — reduce *steady* noise by 20 – 30 dB but do little for impulse peaks. Excellent for travel and offices, not a substitute for proper PPE in industrial settings. ### How to derate the rated NRR in real life The OSHA convention is to derate the labeled NRR by 50 % for foam plugs and by 25 % for muffs to account for imperfect fit. A foam plug labeled 30 dB NRR delivers about 15 dB of real‑world protection. This is one reason musician's plugs (with filtered, predictable response) are often preferred even at lower nominal NRRs — the rated number is closer to what you actually get. For a deeper occupational view of which protector to choose for which workplace, see the [workplace noise standards page](/workplace). ## What to do this week If this article is the prompt to act, the simplest sequence is: 1. **Open the [decibel meter](/) and measure the noisy spaces in your life.** Commute, gym, concert, kitchen, office. Most people overestimate loudness in some places and underestimate it in others. 2. **Cross‑check the readings with the [comparison chart](/comparison)** to make sure the numbers match what you'd expect. 3. **Pick one space above 85 dBA and apply protection or shorter exposure.** The biggest health gains come from the worst sources — concerts and commutes typically dominate the dose. 4. **If you regularly exceed 85 dBA at work, learn the [OSHA / NIOSH compliance picture](/workplace) and ask your employer about the hearing‑conservation program you are entitled to.** 5. **Get a baseline audiogram if you are over 40, work in a noisy environment, or have any tinnitus you'd describe as persistent.** Hearing damage is irreversible, but the rate at which you accumulate it is fully under your control. The instrument in your hand and the protectors on the shelf are the entire toolkit. # Workplace Noise Standards: OSHA, NIOSH, and EU Regulations Explained About **22 million American workers** are exposed to hazardous noise on the job, according to [NIOSH](https://www.cdc.gov/niosh/topics/noise/), making occupational noise the most common preventable workplace illness in the United States. The cost is real and recurring: hearing loss claims account for roughly **$242 million** in workers' compensation each year. This page explains the three frameworks that govern workplace noise — the legally binding OSHA standard, the science‑based NIOSH recommendation, and the EU Directive that covers workers across the European Union — and walks through what a compliant hearing‑conservation program actually looks like in practice. If you are an employer trying to understand your obligations, a worker trying to confirm what your employer owes you, or an EHS consultant building a noise survey, this is the reference. The [live decibel meter](/) on this site is a screening tool — adequate for mapping a facility and identifying high‑exposure areas, not a substitute for a [Class 2 sound‑level meter](/glossary#iec-616721) certified to IEC 61672‑1 when documentation has legal weight. ## Why workplace noise standards exist Sustained occupational exposure to high noise levels causes [noise‑induced hearing loss (NIHL)](/health) — a permanent, sensorineural, and gradually progressive condition. Unlike most occupational injuries, NIHL typically goes unnoticed by the worker until measurable speech‑comprehension deficits appear, by which point the damage is irreversible. The mechanism is covered in detail on the [hearing health page](/health); the regulatory implication is that **prevention is the only viable intervention**, and prevention requires standards. Three threads run through every modern noise standard: a permissible exposure level, an exposure‑time exchange rate, and an action level that triggers mandatory monitoring and protection. Different jurisdictions land on slightly different numbers — but every modern standard agrees that exposure above the 85 – 90 dBA range over an 8‑hour workday is a hazard worth controlling. ## OSHA — 29 CFR 1910.95 The Occupational Safety and Health Administration's noise standard is the federal floor for non‑agricultural private‑sector employers in the United States. It has been in force, with minor amendments, since 1983, and is codified at [29 CFR 1910.95](https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.95). **The headline numbers:** | Threshold | Level | Meaning | |---|---|---| | Permissible Exposure Limit (PEL) | **90 dBA / 8 h TWA** | Above this, engineering or administrative controls are required. | | Action Level (AL) | **85 dBA / 8 h TWA** | Above this, a Hearing Conservation Program (HCP) is mandatory. | | Ceiling | **115 dBA** | No exposure is permitted at or above this level (continuous). | | Impact / impulse | **140 dB peak SPL** | No unprotected exposure to impulses at or above. | | Exchange rate | **5 dB** | Every 5 dB above 90 halves the safe time. | The 5 dB exchange rate means an 8‑hour day at 90 dBA equals a 4‑hour day at 95 dBA equals a 2‑hour day at 100 dBA. This is more permissive than the energy‑equivalent 3 dB rate used by NIOSH and most international standards. **Time‑weighted average formula.** OSHA expresses exposure as a TWA — the 8‑hour energy‑equivalent of whatever variable noise the worker actually saw during the shift: ``` D = sum( C_i / T_i ) × 100 (% dose) TWA = 16.61 × log10( D / 100 ) + 90 (dBA) ``` Where `C_i` is the actual time at level `L_i` and `T_i` is the OSHA‑permitted time at that level. A worker with D = 100 % dose has accumulated exactly the PEL; D > 100 % is over the limit. **What an employer must do above the action level (85 dBA):** - Monitor sound exposure using an SLM or a personal noise dosimeter. - Provide annual audiometric testing at no cost to employees, with a **baseline audiogram** within 6 months of the worker's first exposure above the AL. - Make hearing protectors available, with at least one model from each of three categories (plug, muff, canal cap). - Provide annual hearing‑conservation training. - Keep noise exposure records for 2 years and audiometric records for the duration of employment plus 30 years. **Penalties.** OSHA's General Duty Clause and the noise standard itself are enforced through inspections. Citations average roughly **$15,625 per violation** (FY 2024 baseline), with willful violations escalating up to $156,259. State plans (California, Michigan, Oregon, Washington, and others) operate parallel programs with broadly similar requirements. **Construction.** Construction workers are covered by a separate but similar standard, [29 CFR 1926.52](https://www.osha.gov/laws-regs/regulations/standardnumber/1926/1926.52), with the same 90 dBA / 5 dB / 115 dBA limits. ## NIOSH — the science‑based recommendation The [NIOSH Recommended Exposure Limit (REL)](https://www.cdc.gov/niosh/docs/98-126/) is **85 dBA over 8 hours, with a 3 dB exchange rate**. NIOSH revised this recommendation in 1998 based on dose‑response data accumulated since the OSHA standard was finalized. The agency estimates that compliance with the NIOSH REL leaves an excess risk of material hearing impairment of approximately 8 % over a 40‑year working life — versus ~25 % at the OSHA PEL. **Why the difference matters.** A typical industrial workplace at 95 dBA permits roughly 4 hours of unprotected exposure under OSHA's 5 dB rule but only 1 hour under NIOSH's 3 dB rule. For an employer aligning to NIOSH, the effective protection budget is about 25 % of OSHA's. Most modern EHS programs use NIOSH internally even where OSHA is the legal floor — both because the science is more current and because the gap between NIOSH and OSHA is widely expected to close in any future rulemaking. **Other NIOSH guidance to know:** - [Buy Quiet program](https://www.cdc.gov/niosh/topics/buyquiet/) — purchasing guidance to favor lower‑noise equipment at procurement time, the most cost‑effective form of engineering control. - [Power Tools database](https://www.cdc.gov/niosh/topics/buyquiet/) — measured emission levels for hundreds of construction and manufacturing tools. - [Hierarchy of Controls](https://www.cdc.gov/niosh/hierarchy/) for noise: elimination → substitution → engineering controls → administrative controls → PPE. ## EU — Directive 2003/10/EC The European Union's framework directive on minimum health and safety requirements for workers exposed to noise applies across all 27 member states, supplemented by national transpositions (the UK retains a closely aligned post‑Brexit regulation, the Control of Noise at Work Regulations 2005). The framework is structured around three exposure levels: | Level | Daily exposure | Peak | Required action | |---|---|---|---| | Lower exposure action value | **80 dBA LEX,8h** | 135 dBC | Hearing protection must be **made available**; risk assessment; worker information. | | Upper exposure action value | **85 dBA LEX,8h** | 137 dBC | Hearing protection must be **worn** (mandatory); area marking; access restriction; audiometric testing. | | Exposure limit value | **87 dBA LEX,8h** | 140 dBC | Considered with hearing protection in place — exposure exceeding this **at the ear** must not occur. | The exchange rate is **3 dB**, matching NIOSH. The exposure limit value is the only standard in the world that explicitly accounts for the *attenuation of the protector* — meaning the regulated quantity is the level reaching the worker's ear, not the level at the workstation. Outside the EU, similar 3 dB / 85 dBA frameworks are in force in Canada (province‑level), Australia, New Zealand, and most OECD countries. ## What a Hearing Conservation Program actually contains OSHA, NIOSH, and EU 2003/10 share a common core for what counts as a compliant program. The elements below are necessary; the relative emphasis shifts by jurisdiction. ### 1. Noise monitoring - **Initial survey** — area sound‑level measurements (SLM) at every worker location, plus task‑based monitoring for variable jobs. - **Personal dosimetry** — wearable dosimeters for workers whose exposure varies during the shift, sampling at least one full shift every two years in the US (more frequently in the EU). - **Trigger for re‑survey** — any change in production, equipment, or controls that could plausibly affect exposure. ### 2. Audiometric testing - **Baseline audiogram** within 6 months of first exposure above the action level (US: AL = 85 dBA; EU: 80 dBA upper action). - **Annual audiogram** for as long as the worker remains above the action level, compared against the baseline to detect a **standard threshold shift (STS)**: an average shift of 10 dB or more at 2, 3, and 4 kHz. - **Follow‑up.** When STS is confirmed, the employer must inform the worker in writing within 21 days, refit hearing protection, and consider removing the worker from the high‑noise area. ### 3. Hearing protectors - **Selection** — protectors with adequate attenuation for the highest expected level, derated per OSHA convention (NRR ÷ 2 for foam plugs; NRR × 0.75 for muffs). - **Fit testing** — increasingly common with quantitative fit‑test systems ([3M E‑A‑Rfit](https://www.3m.com/3M/en_US/p/d/v000074340/), Howard Leight VeriPRO) that measure attenuation in the actual ear, not in a laboratory ANSI S12.6 chamber. - **Replacement** — foam plugs daily, premolded plugs as needed, muffs when cushion or hardware degrades. ### 4. Worker training and recordkeeping - Annual training: effects of noise, purpose of audiometric testing, use and care of hearing protection. - Records: noise exposure (2 years OSHA, 5 years EU), audiometric records (employment + 30 years). - Records made available to workers, their representatives, and inspectors on request. ### 5. Engineering and administrative controls The hierarchy is unambiguous: prefer source treatment, then path treatment, only then PPE. - **Source** — quieter equipment at procurement; vibration isolation; enclosure; damping. - **Path** — sound‑absorptive walls and ceilings; barriers; distance (every doubling of distance attenuates ~6 dB in free field). - **Administrative** — job rotation, shorter shifts, scheduled quiet breaks. OSHA explicitly requires "feasible administrative or engineering controls" where exposure exceeds the PEL — feasibility is technical and economic, but the burden is on the employer to demonstrate it is not feasible. ## Industry-specific exposure ranges Typical mid‑range exposures from NIOSH, MSHA, and trade association data. Real readings vary widely by equipment, distance, and process state. | Industry / job | Typical (dBA) | Peak | |---|---|---| | General office | 50 – 65 | 75 | | Call center | 60 – 75 | 90 | | Light assembly | 70 – 85 | 100 | | Food and beverage processing | 80 – 95 | 105 | | Heavy manufacturing (stamping, forging) | 95 – 115 | 130+ | | Construction (general) | 85 – 105 | 120 | | Construction (jackhammer, demolition) | 100 – 120 | 130+ | | Underground mining | 90 – 110 | 130 | | Surface mining (drill, haul truck) | 95 – 115 | 125 | | Aviation maintenance (apron) | 110 – 140 | 150 | | Music venue (FOH) | 95 – 115 | 130 | | Music venue (musician on stage) | 100 – 120 | 130 | | Daycare / school cafeteria | 75 – 95 | 110 | | Restaurant kitchen at peak | 75 – 90 | 100 | For a more detailed environmental‑exposure breakdown with examples and context, see the [noise comparison chart](/comparison). ## Required and recommended equipment A compliant occupational survey program needs the following instruments: - **Class 2 Sound Level Meter** ([IEC 61672‑1](https://www.iec.ch/), ANSI S1.4) — accuracy ±2 dB, typical price US $300 – 800. Sufficient for area measurements at the OSHA action level. Class 1 (±1 dB) is required for some research and rule‑of‑evidence settings. - **Personal noise dosimeter** (ANSI S1.25) — body‑worn, integrating, with shoulder‑mounted microphone. Required for variable‑exposure jobs (most construction, maintenance, and field service work). - **Calibrator** (IEC 60942 Class 2) — produces a 94 dB or 114 dB reference tone at 1 kHz, used to verify the SLM and dosimeter at the start and end of each survey day. - **Audiometer** (ANSI S3.6) — for the audiometric‑testing portion of the HCP. Most US employers contract this out to a mobile service or local audiology clinic. A browser‑based decibel meter is **not** a compliance instrument. It is a useful screening tool for mapping a facility, identifying problem areas, and giving frontline workers visibility into their own exposure. For documentation that holds up to OSHA inspection or workers' compensation claims, use a calibrated Class 2 SLM or dosimeter. ## How to audit your workplace — the 60‑minute walkthrough If you suspect you have a noise problem and want to know whether to invest in a full survey, this lightweight walkthrough takes about an hour. 1. **Map the floor.** Mark every machine, workstation, and walkway on a simple plan. Note operating cycles (which machines are usually running simultaneously). 2. **Measure mid‑shift.** Walk the floor with the [browser meter](/) on a phone held at chest level, recording the reading at each location for 30 seconds. Note A‑weighted, slow time‑weighted readings. 3. **Identify hotspots.** Any reading above 85 dBA is a candidate for formal monitoring. Anything above 95 dBA at a continuously occupied workstation is a near‑certain compliance problem. 4. **Check protector availability.** Verify that hearing protectors are stocked at every entry to a high‑noise area, and that signage marks the area as a hearing‑protection zone. 5. **Schedule a Class 2 survey.** If two or more locations exceed 85 dBA, you have a formal hearing‑conservation obligation under either OSHA (US) or 2003/10 (EU). Bring in a certified industrial hygienist for the next step. The browser meter result is good enough to know whether to engage the hygienist. It is not good enough to defend in an inspection report. ## Reference and further reading The full text of the standards above: - [OSHA 29 CFR 1910.95](https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.95) — General Industry occupational noise. - [OSHA 29 CFR 1926.52](https://www.osha.gov/laws-regs/regulations/standardnumber/1926/1926.52) — Construction occupational noise. - [NIOSH Publication 98‑126](https://www.cdc.gov/niosh/docs/98-126/) — Criteria for a Recommended Standard: Occupational Noise Exposure. - [EU Directive 2003/10/EC](https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32003L0010) — Workers exposed to noise. - [MSHA 30 CFR Part 62](https://www.ecfr.gov/current/title-30/chapter-I/subchapter-O/part-62) — Mining noise exposure. For background on the biology underpinning all of this, see the [hearing health page](/health). For source‑level context (what does 100 dBA actually sound like in different industries?), see the [comparison chart](/comparison). For glossary entries on every acronym in this article — TWA, REL, PEL, NRR, STS, HCP, dBA, LEX,8h — see the [glossary](/glossary). # Real-World Use Cases: When and Why to Measure Sound Levels A [decibel meter](/) is most useful when you have a specific question that the number can answer. "Is this room too loud for sleep?" "Is my office quiet enough to focus?" "Will this concert damage my hearing in the time I plan to be there?" Each scenario has a different acceptable range, a different standard, and a different intervention if the reading comes back wrong. This page collects the most common situations where people reach for a sound‑level meter, with the published thresholds for each and the practical action you can take. The numbers below come from [WHO](https://www.who.int/news-room/fact-sheets/detail/deafness-and-hearing-loss), [NIOSH](https://www.cdc.gov/niosh/topics/noise/), [CDC](https://www.cdc.gov/nceh/hearing_loss/), [EPA](https://www.epa.gov/clean-air-act-overview/epa-history-noise-and-noise-control-act), and [ANSI](https://webstore.ansi.org/) standards where applicable. Where specific products are useful (white‑noise machines, hearing protectors), they are mentioned for context — the [hearing health page](/health) is the deeper reference. ## Baby and children's bedrooms **Target level:** 30 – 35 dBA LAeq during sleep (WHO recommendation). Sleep research consistently shows that bedroom noise above ~35 dBA disrupts sleep architecture in adults and children, even when the sleeper does not consciously wake. For infants, the developing auditory system is more sensitive to disruption — the [WHO Environmental Noise Guidelines](https://www.who.int/europe/publications/i/item/9789289053563) recommend keeping nighttime levels at 30 dBA inside the bedroom and 40 dB Lnight outside it. White‑noise machines are popular and useful, but they are also the most common cause of accidental over‑exposure for infants. A 2014 study in *Pediatrics* found that 85 % of commercial infant sleep machines could produce over 85 dBA at maximum volume at 30 cm — enough to exceed occupational limits if used overnight. Best practice: - Place the machine **at least 2 m from the crib**. - Set the volume so the level **at the crib position** is 50 dBA or less, measured with a calibrated meter. - Time‑limit the machine if your model supports it; continuous overnight operation is not necessary. For children's rooms, the same WHO 30 dBA target applies, but schools and classrooms have their own standard, [ANSI S12.60](https://webstore.ansi.org/standards/asa/ansiasa1260201) — 35 dBA background and 0.6 s reverberation time. Most cafeterias and gymnasiums substantially exceed both. ## Home office and remote work **Target level:** 40 – 55 dBA for focused work, 50 – 65 dBA acceptable for collaborative work. Studies from UC Berkeley's Center for the Built Environment and the British Council for Offices converge on the same finding: **above ~55 dBA LAeq, focused cognitive work measurably degrades**. Open‑plan offices typically run 60 – 75 dBA during the work day; the productivity drop relative to a private office at 50 dBA is on the order of 15 – 30 % for tasks involving reading, writing, or complex reasoning. For people working from home: - **Refrigerators** in adjacent rooms typically add 40 – 45 dBA at the desk. Mostly fine, but worth knowing. - **HVAC** at the supply diffuser ranges 35 – 50 dBA. Older systems are noisier; newer ECM blowers are quieter. - **Outdoor traffic** through a closed double‑pane window adds about 10 – 15 dB to the indoor level relative to outdoor — so an outdoor street at 70 dBA reads about 55 – 60 dBA at the desk by the window. - **Active noise‑cancelling headphones** subtract 20 – 30 dB of low‑mid frequency noise but pass voice. Often the simplest intervention. If your home office reads above 60 dBA during work hours and you cannot move the desk, the highest‑value intervention is usually addressing the loudest single source — a noisy fan, a refrigerator, an open window — not broad treatment of the whole room. ## Concerts, clubs, and live music **Typical levels:** 95 – 120 dBA; well above hearing‑damage thresholds. A single 100 dBA hour exceeds the [NIOSH 8‑hour budget](/health#exposure-time-chart-niosh) by about 4×; a 110 dBA front‑row spot exhausts the daily budget in about 90 seconds. Concerts and clubs are the single largest source of preventable adult hearing loss in the developed world. Practical guidance: - **Filtered earplugs** (Loop, Eargasm, Etymotic ER‑20) deliver 15 – 25 dB of attenuation with a flatter response than foam plugs, so music still sounds like music. A 20 dB plug at a 110 dBA show drops the at‑ear exposure to 90 dBA — meaning the 8‑hour NIOSH budget becomes ~2 – 4 hours, much longer than the show. - **Position matters.** The drop‑off from front‑row to mid‑venue is typically 6 – 10 dB. The back of a 110 dBA arena is closer to 100 dBA — still loud, but with three to four times the safe duration. - **For musicians**, custom‑molded plugs or in‑ear monitors are the standard. The [hearing health page](/health#earplugs) covers the options in detail. ## Construction and DIY power tools **Typical levels:** 85 – 120 dBA at the operator. The OSHA construction noise standard, [29 CFR 1926.52](https://www.osha.gov/laws-regs/regulations/standardnumber/1926/1926.52), applies to professionals; for DIY, the same biological thresholds apply even without a regulatory framework. Common levels: | Tool | Typical (dBA) at operator | |---|---| | Cordless drill | 80 – 90 | | Circular saw | 100 – 110 | | Mitre saw | 95 – 105 | | Angle grinder | 95 – 110 | | Hammer drill | 100 – 115 | | Belt sander | 90 – 100 | | Air compressor (small) | 75 – 85 | | Pneumatic nailer | 95 – 105 | | Chainsaw | 105 – 115 | | Leaf blower | 95 – 110 | | Lawn mower (gas) | 85 – 100 | Wear hearing protection any time you use a tool above 85 dBA — and that's almost any tool more powerful than a screwdriver. NRR 25 – 30 dB foam plugs, properly inserted, are sufficient for everything in this table. For repeated use of impulse tools (nail guns, hammers), passive or electronic earmuffs add a useful margin. Local noise ordinances also apply to outdoor work. Most US municipalities permit residential outdoor noise of 60 – 65 dBA daytime / 50 – 55 dBA night at the property line; running power tools before 7 a.m. or after 10 p.m. typically violates ordinance. ## Gym and group fitness classes **Typical levels:** 85 – 110 dBA in spinning, HIIT, dance classes. Music‑driven group classes routinely run hot. A 2018 study in the *Journal of Public Health Policy* surveyed 17 fitness studios in 5 US cities and found average class levels of **101 dBA**, with peaks above 115 dBA. That puts a 60‑minute class well over the NIOSH daily budget. For instructors, this is occupational exposure under EU Directive 2003/10/EC and analogous frameworks worldwide. Most studios do not provide hearing protection or audiometric testing, despite a clear compliance obligation. For participants: - Bring filtered earplugs to high‑intensity classes. They reduce the music to a comfortable mid‑80s level without killing the energy. - Position yourself further from speakers when possible; it can buy 3 – 6 dB. - If a particular studio is consistently above 100 dBA, raise it with management — they may genuinely not know. ## Classrooms and lecture halls **Standard:** ANSI S12.60 — 35 dBA background, 0.6 s reverberation time. Speech intelligibility for children depends on a high signal‑to‑noise ratio. A teacher's voice at 65 dBA in a 50 dBA room (15 dB SNR) is intelligible to nearly all students; the same voice in a 60 dBA room (5 dB SNR) leaves the back rows guessing. The effect compounds for non‑native speakers, students with mild hearing loss, and students with ADHD. Most US K‑12 classrooms fail ANSI S12.60. The most common culprits, in order, are: 1. HVAC at the supply diffuser (often 50 – 60 dBA). 2. Outdoor traffic transmitted through windows. 3. Adjacent classrooms (rolling doors, thin partitions). 4. Reverberation from hard floors and bare walls. Acoustic treatment (carpet, absorptive ceiling tile, drapes) addresses reverb cheaply; HVAC and isolation require more investment. If you are on a school board or a parent advocate, the ANSI S12.60 standard is the appropriate evidence base. ## Restaurants, cafes, and bars **Comfort threshold:** 70 dBA for normal conversation. Above 70 dBA, conversational effort climbs sharply. Above 80 dBA, most people raise their voices substantially, which raises the room level further (the "Lombard effect"). A noisy restaurant at 85 dBA is louder than the patrons' actual speech alone would predict — they are unconsciously competing with the room. Some published references for context: - A quiet cafe at off‑hours: 55 – 65 dBA. - A typical restaurant at dinner peak: 70 – 80 dBA. - A trendy "loud" restaurant at peak: 85 – 95 dBA. - A bar with live music: 95 – 110 dBA. Apps like SoundPrint crowdsource restaurant noise levels — useful when choosing a venue for a date or a business meeting where you actually want to hear each other. For people with hearing loss or processing disorders, even "comfortable" restaurants at 75 dBA can be unintelligible. Restaurant‑guide loudness tags (Zagat, Michelin's "atmosphere" indicator) are increasingly common; if you measure a place yourself, take readings in three positions during peak hour and report the mean. ## Real estate and apartment hunting **Typical evaluation thresholds:** - Bedroom (window closed): under 40 dBA target, 45 dBA acceptable. - Living room: under 50 dBA target. - Kitchen, bathroom: not noise‑sensitive. Apartment shopping in a city often comes down to noise. Standard walkthroughs are during the day, when the worst sources (late‑night traffic, neighbors' bass, building HVAC) are masked. Best practice: 1. Measure with windows closed during the busiest realistic hours (rush hour traffic, Friday night, garbage pickup morning). 2. Check the floor and ceiling — knock on both. Solid concrete transmits less impact noise than wood frame or steel deck. 3. Open every window once with the meter running, to know the outside‑inside differential. A single‑pane window typically gives 15 – 20 dB attenuation; a modern double‑pane gives 25 – 30 dB. 4. If you measure above 50 dBA inside the bedroom of an apartment you are considering, walk away or expect to add interior storm windows. A meter reading is also useful evidence in noise‑related disputes with neighbors or landlords. Future versions of our tool will support data export with timestamp logs — a long‑standing roadmap item — so that meter data can support a written complaint. ## Vehicle cabins **Typical levels:** 60 – 80 dBA at highway speed. Cabin noise affects long‑haul comfort, fatigue, and (over years) cumulative hearing exposure. Modern cars get progressively quieter: - Hybrid or EV at highway speed: 60 – 72 dBA. - Modern ICE sedan at highway speed: 65 – 75 dBA. - Older ICE sedan or compact: 70 – 82 dBA. - Pickup truck or SUV at highway speed: 70 – 80 dBA. - Motorcycle (rider's helmet): 90 – 105 dBA. Two hours daily at 75 dBA is well under NIOSH limits, but cumulative fatigue from cabin noise reduces highway alertness. For motorcyclists, the rider's helmet position routinely exceeds 90 dBA — earplugs under the helmet are standard practice for any ride longer than ~30 minutes. ## Putting it all together The pattern across all of these scenarios is the same: there is a **published target level**, a **typical measured range**, and a small number of **interventions** that move the actual level toward the target. A decibel meter is most useful when you treat the reading as the input to a decision, not as an end in itself. Read the [comparison chart](/comparison) for the level‑by‑activity reference. Read the [hearing health page](/health) for the underlying why. Read the [workplace standards page](/workplace) if your scenario is on the job. Read the [glossary](/glossary) if a term in this page needs unpacking. Then [open the meter](/) and find out where your environment actually sits. # The Science of Sound: Decibels, Frequencies, and Hearing Explained Every reading on a [decibel meter](/) is the visible end of a chain of physics, signal processing, and psychoacoustics. Understanding that chain makes the readings useful — you stop asking "is 90 dB loud?" and start asking the more useful questions: 90 dB compared to what reference, through what weighting filter, integrated over what time window. This page works through the physics of sound waves, the math of the decibel scale, the four standard frequency weightings, equal‑loudness contours, time integration, and FFT spectrum analysis. By the end you should be able to read any published noise number and know exactly what it does and does not mean. This is the longest technical page on the site. If you are here to learn, read top to bottom. If you are here to look up a specific concept, the [glossary](/glossary) cross‑links to the relevant section of this page for every term. ## Sound is a pressure wave Sound is a longitudinal wave of pressure variation propagating through an elastic medium — usually air. A vibrating source compresses the air in front of it, then rarefies it as it moves back, and that compression‑rarefaction pattern travels outward at the speed of sound (roughly **343 m/s** in air at 20 °C, slower in cold air, faster in warm or in denser media like water). The physical quantity a microphone responds to is **pressure** — the difference between the instantaneous local air pressure and the steady atmospheric pressure. Atmospheric pressure is about **101,325 Pa** (101 kPa); the smallest sound a healthy young ear can detect — the **threshold of hearing** at 1 kHz — is a pressure variation of about **20 micropascals (20 µPa)**, or 20 × 10⁻⁶ Pa. The threshold of pain sits around 20 Pa, a million times higher. That ratio of a million in pressure is what motivates the logarithmic decibel scale. Working with linear pascals across that range produces unwieldy numbers (compare 0.00002 to 20). Compressing the range logarithmically produces 0 dB to 120 dB, which is much easier to write down and reason about. A pressure wave has three key descriptors: - **Amplitude** — the magnitude of pressure variation. Maps to loudness, with strong nonlinearities (see [equal‑loudness](#equal-loudness-contours) below). - **Frequency** — the number of compression‑rarefaction cycles per second, measured in hertz (Hz). Maps to pitch, again with nonlinearities. - **Phase** — where in the cycle the wave currently is. Mostly irrelevant for level measurements, important for interference and multi‑microphone setups. For a pure sine tone, those three numbers fully describe the signal. Real sounds are almost never pure tones — they are sums of many components at different frequencies, each with its own amplitude and phase, varying continuously over time. ## The decibel scale The decibel is **not a unit** — it is a logarithmic ratio between two quantities, made into a usable number by reference to a fixed denominator. For sound pressure level (SPL), the standard reference is 20 µPa. Given a measured pressure `p`, the SPL in decibels is: ``` L_p = 20 × log10( p / p_0 ) where p_0 = 20 µPa ``` The factor of 20 (rather than 10) is because pressure is proportional to the square root of intensity, and the decibel is a **power ratio**. For acoustic intensity: ``` L_I = 10 × log10( I / I_0 ) where I_0 = 1 pW/m² ``` In free field, both formulas yield the same number, which is why most people use them interchangeably and why "dB" is a meaningful answer without specifying which. Three rules of thumb fall directly out of the math: - **+3 dB doubles the acoustic energy.** Two identical incoherent sources (each 60 dB) sum to 63 dB, not 66 dB. Three identical sources sum to 60 + 10 log10(3) ≈ 64.8 dB. - **+10 dB is roughly 2× as loud** to a human listener. The 10× intensity increase is compressed to a roughly 2× perceived loudness by the nonlinearity of human hearing. - **+6 dB doubles the pressure** but only adds 4× the intensity. This matters for distance: a point source in free field doubles its distance and the SPL drops by 6 dB. The decibel scale also has variants that confuse newcomers: - **dB SPL** — the pressure scale described above. The default for acoustic measurements. - **dB FS** (decibel full scale) — used in digital audio. 0 dB FS is the maximum representable digital sample value; everything else is negative. Cannot be directly compared to dB SPL without a reference calibration. - **dB SWL** (sound power level) — the absolute power radiated by a source, regardless of where you measure it. Used for equipment ratings. - **dBA / dBC / dBZ** — A, C, or Z weighting applied to a dB SPL measurement. Always specify the weighting alongside the number. ## Frequency and pitch The human ear responds to pressure variations from about **20 Hz** at the low end to about **20 kHz** at the high end, with the upper limit declining steadily with age (a typical 60‑year‑old hears up to about 12 kHz). Below 20 Hz is **infrasound** (felt more than heard); above 20 kHz is **ultrasound** (a dog whistle is around 25 kHz; medical ultrasound is in the megahertz range). Two scales are used to measure frequency intervals: - **Octaves** — a doubling of frequency. 100 Hz to 200 Hz is one octave; 200 Hz to 400 Hz is the next. The audible range is roughly 10 octaves. - **One‑third octaves** — three bands per octave, traditional in acoustic measurements because they roughly approximate the ear's frequency resolution. ISO 266 specifies the standard center frequencies (...100, 125, 160, 200, 250, 315, 400...). Real sounds have **broadband** content: a vacuum cleaner is energy spread across many frequency bands; a tuning fork is concentrated at a single frequency. Most environmental noise is broadband; most musical notes are pseudo‑tonal (a fundamental plus harmonics). ## Frequency weightings The human ear is not equally sensitive to all frequencies — far from it. A 60 dB tone at 1 kHz sounds significantly louder than a 60 dB tone at 50 Hz, because the ear is more sensitive in the mid range and much less so at the low end (and somewhat less so above ~5 kHz). A measurement microphone is, by design, **flat** — its electrical output is proportional to acoustic pressure across the audible range. That flatness is the right starting point, but it means the raw measurement does not reflect how a human listener experiences the sound. To bridge that gap, sound‑level meters apply a **frequency weighting filter** before computing the level. Four weightings are standardized in [IEC 61672‑1](https://www.iec.ch/), named historically by letter: ### A‑weighting Approximates the inverse of the 40‑phon equal‑loudness contour. Heavily attenuates frequencies below 500 Hz (about −30 dB at 50 Hz, −40 dB at 20 Hz) and slightly above 6 kHz; nearly flat in the 1 – 5 kHz range where the ear is most sensitive. Used for nearly all occupational and environmental noise (NIOSH, OSHA, WHO, ISO 1996, EU 2003/10). The mathematical form is a 4‑pole, 4‑zero analog filter: ``` R_A(f) = (12194² × f⁴) / [ (f² + 20.6²) × √((f² + 107.7²)(f² + 737.9²)) × (f² + 12194²) ] A(f) = 20 × log10( R_A(f) ) + 2.00 dB ``` The +2.00 dB offset normalizes A‑weighting to 0 dB at 1 kHz. ### C‑weighting Much flatter than A. Attenuates only at the extreme ends of the audible range (about −3 dB at 31.5 Hz and at 8 kHz; about −0.2 dB at 50 Hz). Used for **peak measurements** (where the actual peak energy matters more than its perceived loudness), for **low‑frequency** sources like concerts, subwoofers, and thunder, and historically for high‑level sounds where the ear's frequency response approaches a 40 – 100 phon contour rather than the 40‑phon contour A‑weighting approximates. ### B and D weightings B was an intermediate level weighting, intended for moderate sound levels (50 – 60 phon). D was specific to aircraft noise. Both have been deprecated by modern standards and you will rarely encounter them in practice. ### Z‑weighting Zero weighting — a flat response across 10 Hz to 20 kHz. Used for research and instrument verification. Replaced the older "linear" or "unweighted" terminology, which was inconsistent across manufacturers. When in doubt, use A‑weighting. When measuring something bass‑dominated, also report C‑weighting; the gap between A and C is itself diagnostic of the spectral content. ## Equal‑loudness contours The frequency dependence of human hearing is not a single curve — it varies with level. At low SPLs, you are very insensitive to low frequencies; at high SPLs, the curve flattens. The classic experimental data is **Fletcher and Munson 1933**, with modern revisions standardized as **ISO 226:2003**. Both produce a family of curves, each labeled with a **phon** value, where the phon is the SPL of a 1 kHz tone perceived as equally loud as the test tone. So the 40‑phon contour shows the SPL needed at each frequency to sound as loud as a 40 dB SPL tone at 1 kHz. A few practical implications: - A‑weighting models the 40‑phon contour, so it is most accurate for moderate listening levels (40 – 60 dB SPL). At high levels (> 90 dB SPL), A‑weighting under‑weights low frequencies relative to how the ear actually responds. - The **phon** is a unit of loudness level, not loudness itself. - The **sone** is a unit of perceived loudness, defined so that a doubling of sones corresponds to a doubling of perceived loudness. 1 sone = 40 phon. 2 sones = 50 phon (the +10 phon = 2× loudness rule). ## Time integration A microphone reports an instantaneous pressure value many thousands of times per second. Reporting any single sample as "the level" is useless — instead, sound‑level meters compute a **time‑weighted RMS** over a chosen integration time: ``` p_rms(t) = sqrt( (1/τ) × integral( p²(s) × e^(-(t-s)/τ) ) ds ) ``` The time constant `τ` defines the response speed: - **Fast (F)** — `τ = 125 ms`. The default for environmental and occupational measurements. - **Slow (S)** — `τ = 1000 ms`. For steady ambient noise. - **Impulse (I)** — `τ_attack = 35 ms`, `τ_decay = 1500 ms`. Captures brief transients (gunshots, hammer strikes). For noise that varies significantly over time, the time‑weighted SPL flickers. Most regulatory standards use the **equivalent continuous level** (`Leq` or `LAeq` for A‑weighted) instead — the steady SPL that delivers the same total acoustic energy as the actual variable signal: ``` LAeq,T = 10 × log10( (1/T) × integral( 10^(LA(t)/10) ) dt ) ``` `Leq` is energy‑equivalent, additive across time, and the basis of every modern occupational noise standard. Other statistical descriptors are sometimes used for community noise: - **L10, L50, L90** — the level exceeded 10 %, 50 %, 90 % of the measurement period. L10 is a "peak typical" level; L90 is a "background" level. - **Lden** — a day‑evening‑night weighted average used in EU community‑noise mapping. Penalizes evening levels by +5 dB and night levels by +10 dB. - **Lmax, Lpeak** — single‑event maximum and peak‑pressure levels. Lmax is time‑weighted; Lpeak is the instantaneous unweighted peak. ## FFT and spectrum analysis A pressure waveform in the time domain can be transformed into the frequency domain using the **Fast Fourier Transform (FFT)**. The FFT takes a window of audio samples and produces a complex spectrum showing the amplitude and phase of each frequency bin within the window. A few properties of the FFT every user should know: - **Bin resolution = sample_rate / FFT_size.** A 48 kHz sample rate with a 2048‑point FFT gives 23.4 Hz per bin — fine for music and speech, coarse for low‑frequency analysis where 1‑Hz resolution may be needed. - **Window function** — multiplying the time samples by a window (Hann, Hamming, Blackman, Kaiser) before the FFT reduces spectral leakage at the cost of broader main lobes. Our visualizer uses a Hann window. - **Time‑frequency uncertainty.** Larger FFT windows give finer frequency resolution but coarser time resolution. There is no way to have both — Heisenberg, applied to acoustics. For environmental and occupational measurements, **1/3‑octave** analysis is more useful than narrow‑band FFT. A 1/3‑octave analyzer groups the FFT bins into perceptually meaningful bands (the same ones the ear approximately resolves), which makes the resulting spectrum readable and comparable to standard noise‑rating curves (NC, RC, NR). The visualizer in our [meter](/) shows narrow‑band FFT for diagnostic purposes — it makes tonal sources jump out as single peaks. For formal frequency analysis, use a Class 2 SLM with built‑in 1/3‑octave bands. ## Tying it back to the meter Every number on the [decibel meter](/) is the result of: 1. Sampling air pressure at the microphone (the [calibration page](/calibration) covers what can go wrong here). 2. A‑weighting the digital signal (or C, or Z, depending on settings). 3. Squaring, time‑weighting (Fast / Slow / Impulse), and rooting to produce an RMS pressure. 4. Taking 20 × log10 of the ratio to 20 µPa. 5. Adding the user calibration offset. Knowing the chain doesn't change the readings, but it tells you why two meters can disagree: different microphone calibrations, different weightings, different integration times, different reference values. When numbers don't match, the answer is almost always somewhere in this chain. For practical interpretation of the readings — what counts as loud, what's safe, what regulations apply — see the [comparison chart](/comparison), [hearing health page](/health), and [workplace standards page](/workplace). For term definitions, the [glossary](/glossary) is the index back into this page. # Sound Measurement Glossary: Acoustics and Hearing Terms Explained This glossary collects the most common terms in sound measurement, hearing health, and occupational noise — defined in plain language, with cross‑links to deeper coverage on the rest of the site. Use it as a quick reference when reading the [science page](/science), the [workplace standards page](/workplace), or any technical document that assumes familiarity with the vocabulary. ## A ### A‑weighting (dBA) A frequency weighting filter applied to sound pressure level measurements that approximates the response of human hearing at moderate listening levels. A‑weighting heavily attenuates low frequencies (about −30 dB at 50 Hz) and slightly attenuates above 6 kHz, leaving the 1 – 5 kHz range nearly flat where the ear is most sensitive. Almost every modern noise standard — NIOSH REL, OSHA PEL, WHO community guidelines, ISO 1996, EU 2003/10 — specifies A‑weighting. See [frequency weightings](/science#frequency-weightings). ### Acoustic trauma A sudden, severe hearing loss caused by a single high‑intensity exposure — typically an explosion, a gunshot at close range, or an industrial accident. Distinct from gradual noise‑induced hearing loss because the mechanism is mechanical disruption rather than metabolic exhaustion of the cochlear hair cells. Damage may include ruptured eardrum and disrupted ossicular chain in addition to cochlear injury. ### Action level The exposure level at which a hearing‑conservation program becomes mandatory under occupational regulations. In OSHA 29 CFR 1910.95 the action level is **85 dBA / 8 h TWA** (the PEL is 90 dBA, but mandatory audiometric testing and worker training begin at 85). EU Directive 2003/10/EC has two action values: lower at 80 dBA, upper at 85 dBA. See [workplace standards](/workplace). ### AGC (Automatic Gain Control) A signal‑processing feature found in most consumer microphones and recording chains that automatically adjusts input gain to keep the recorded level near a target. AGC is helpful for voice calls and casual recording but actively harmful for sound‑level measurement because it makes the relationship between the actual SPL and the digital sample value time‑varying and non‑linear. Our browser meter requests `autoGainControl: false` from the OS; consumer devices vary in how strictly they honor that flag, which is one reason [calibration](/calibration) matters per device. ### ANSI S1.4 The American National Standard specifying the performance and calibration requirements for sound‑level meters. The international counterpart is IEC 61672‑1. Both define **Class 1** (precision, ±1 dB tolerance) and **Class 2** (general purpose, ±2 dB tolerance) performance grades. Most occupational compliance instruments are Class 2. ### Audiogram A graph of hearing thresholds across frequencies, used to characterize a person's hearing. Produced by an audiometer in a sound‑treated booth. A baseline audiogram before occupational exposure and an annual follow‑up are required by OSHA 29 CFR 1910.95 for workers above the 85 dBA action level. The classic NIHL signature is a "notch" — a sharper drop at 4 kHz than at adjacent frequencies — visible even when the rest of the audiogram is normal. ## B ### Background noise The ambient sound level present at a location with the source of interest absent. For a measurement to be valid, the background should be at least 10 dB below the target level (the source is at least 10 dB above the background). Background between 6 and 10 dB below requires a correction; background within 6 dB of the target makes the measurement unreliable. ### Basilar membrane The membrane inside the cochlea on which the sensory hair cells sit. Its mechanical tuning maps frequency to position: high frequencies vibrate the base near the oval window, low frequencies vibrate the apex. Damage to the base is the early signature of NIHL because the base sees the highest acoustic stress. ## C ### C‑weighting (dBC) A flat‑ish frequency weighting used for peak measurements and for sources dominated by low‑frequency content (concerts, subwoofers, thunder, fireworks). C‑weighting is nearly flat from 31.5 Hz to 8 kHz, with only a few dB attenuation at the extremes. Always specified alongside the level: "100 dBC" not just "100 dB." ### Cochlea The fluid‑filled spiral organ in the inner ear that transduces sound pressure into neural signals. Contains roughly 15,000 sensory hair cells arranged on the basilar membrane. Mammalian cochlear hair cells do not regenerate, which is why noise damage is permanent. See [hearing health](/health#how-sound-damages-the-ear). ## D ### Decibel (dB) A logarithmic unit expressing the ratio between two values, used in acoustics for sound pressure level (SPL), sound intensity, and sound power. The decibel is **not a unit** in the SI sense; it requires a reference value to be meaningful. For sound pressure, the reference is **20 µPa** (the threshold of hearing at 1 kHz), and the formula is `L = 20 × log10(p / 20 µPa)`. See [the decibel scale](/science#the-decibel-scale). ### dBA, dBC, dBZ Decibel sound pressure level with A, C, or Z (zero, flat) weighting applied. Each weighting yields a different number for the same physical sound. Always specify which weighting was used when reporting a measurement. ### dB FS (full scale) A digital‑audio scale in which 0 dB FS is the maximum representable sample value. Used in DAWs and audio production. Cannot be directly compared to dB SPL without a reference calibration that maps a known acoustic pressure to a known sample value. ### dB SPL (sound pressure level) A decibel value with reference to **20 micropascals (20 µPa)** of air pressure variation. The default scale for environmental and occupational acoustics. The number you see on a sound‑level meter is dB SPL unless explicitly noted otherwise. ### Dynamic range The ratio between the loudest and quietest signals a system can handle. The healthy human ear has a dynamic range of about 120 dB (from threshold of hearing at 0 dB SPL to threshold of pain near 120 dB SPL). Sound‑level meters typically cover 25 – 130 dB SPL. ## E ### Equal‑loudness contour A curve on a frequency‑vs‑SPL plot showing combinations of frequency and SPL that are perceived as equally loud. Standardized in **ISO 226:2003** and originally measured by Fletcher and Munson in 1933. The curves explain why A‑weighting is shaped the way it is and why it works best at moderate listening levels. ### Exchange rate The number of decibels by which the safe exposure time halves. NIOSH and most international standards use **3 dB** (energy‑equivalent: every 3 dB doubles the acoustic energy). OSHA uses **5 dB** for historical reasons. The exchange rate is one of the largest practical differences between the OSHA PEL and the NIOSH REL. ## F ### FFT (Fast Fourier Transform) An efficient algorithm for transforming a time‑domain signal into a frequency‑domain representation. The visualizer in our [meter](/) performs an FFT on each window of microphone samples and displays the magnitude of each frequency bin. FFT bin resolution equals sample_rate / FFT_size — for a 48 kHz signal with 2048 samples per window, each bin spans 23.4 Hz. ### Free field An idealized acoustic environment with no reflective surfaces — sound propagates outward from the source unimpeded. Approximated by anechoic chambers and (less perfectly) by open outdoor spaces. In free field, the inverse‑square law applies: doubling the distance from a point source reduces the SPL by 6 dB. ### Frequency The number of complete oscillations per second in a periodic signal, measured in **hertz (Hz)**. The audible range for healthy young humans is 20 Hz to 20 kHz. Frequencies below 20 Hz are infrasound; above 20 kHz, ultrasound. ## H ### Hair cell A sensory cell in the cochlea that converts mechanical motion of the basilar membrane into neural signals. Mammals have ~15,000 in each ear: 3,500 inner hair cells (the actual transducers) and 12,000 outer hair cells (mechanical amplifiers). Hair cells damaged by noise do not regenerate. ### Hearing Conservation Program (HCP) The set of activities required by occupational noise standards once exposure exceeds the action level. Includes monitoring, audiometric testing, hearing protectors, training, and recordkeeping. Full breakdown on the [workplace standards page](/workplace#what-a-hearing-conservation-program-actually-contains). ### Hertz (Hz) The SI unit of frequency: cycles per second. 1 Hz = one cycle per second; 1 kHz = 1,000; 20 kHz = 20,000. ### Hyperacusis Reduced tolerance to ordinary sound levels — sounds that other people find comfortable feel uncomfortably loud. Often associated with tinnitus and noise‑induced damage; sometimes a symptom of underlying neurological conditions. ## I ### IEC 61672‑1 The international standard specifying the performance and calibration of sound‑level meters. Defines Class 1 (precision, ±1 dB) and Class 2 (general purpose, ±2 dB) performance categories. Compliance instruments for occupational and environmental noise must be IEC 61672‑1 certified. ### Impulse weighting (I) A time weighting with a fast attack (35 ms) and slow decay (1.5 s), designed to capture brief loud events. Used for measurements of impulsive noise sources — gunshots, hammer strikes, balloon pops — and required by some standards for occupational measurements with prominent impulses. ### ISO 1996 The international standard for environmental noise measurement. Two parts: 1996‑1 covers terminology and quantities; 1996‑2 covers field measurement procedures. The reference for community noise mapping, traffic noise studies, and most environmental impact assessments. ## L ### LAeq The A‑weighted equivalent continuous sound pressure level — the steady‑state SPL that would deliver the same total acoustic energy as the actual variable signal over a measurement period. Formally: `LAeq,T = 10 × log10((1/T) × integral(10^(LA(t)/10) dt))`. The energy‑equivalent quantity used in nearly every modern occupational and community noise standard. ### Lden A 24‑hour weighted average level used in EU community noise mapping. Penalizes evening noise (+5 dB) and night noise (+10 dB). The WHO 2018 guideline value for road traffic is 53 dB Lden outdoors. ### Leq The equivalent continuous sound pressure level — same definition as LAeq but without specifying a frequency weighting. Most commonly seen as LAeq (A‑weighted) or LCeq (C‑weighted). ### L10, L50, L90 Statistical descriptors of variable noise. L10 is the level exceeded 10 % of the measurement period (a "peak typical" level), L50 is the median, L90 is the level exceeded 90 % of the time (a "background" level). Useful for community noise where Leq alone hides the distribution of events. ### Lmax, Lpeak Single‑event maxima. Lmax is the highest **time‑weighted** level during the measurement (using Fast, Slow, or Impulse weighting). Lpeak is the highest **instantaneous unweighted** sample value, which catches very brief peaks that time weighting would average out. ### Logarithmic scale A scale on which equal increments correspond to equal **ratios** rather than equal differences. The decibel scale is logarithmic; +10 dB is a 10× ratio in intensity at every level on the scale. Logarithmic scales compress wide ranges into manageable numbers and approximately match how humans perceive many sensory quantities (loudness, brightness, pitch). ## M ### Microphone (omnidirectional vs directional) A transducer that converts air pressure into an electrical signal. An **omnidirectional** mic has equal sensitivity in all directions; a **directional** mic (cardioid, hypercardioid, shotgun) has reduced sensitivity off‑axis. Sound‑level meters typically use omnidirectional mics so that the reading depends on the actual SPL at the mic position, not on which way the mic is pointing. Phone microphones are often directional or have software beam‑forming, which is one reason [calibration](/calibration) is per‑device. ## N ### NIHL (Noise‑Induced Hearing Loss) Permanent sensorineural hearing loss caused by exposure to loud sound, either gradually over years (chronic NIHL) or from a single high‑level event (acoustic trauma). The second most common form of sensorineural hearing loss after age‑related decline. Almost entirely preventable; not currently reversible. Background on the [hearing health page](/health). ### NIOSH REL (Recommended Exposure Limit) NIOSH's recommended occupational noise exposure limit: **85 dBA over an 8‑hour TWA, with a 3 dB exchange rate**. More protective than the OSHA PEL. The de facto international standard for non‑US employers and for US employers practicing best‑in‑class hearing conservation. ### NRR (Noise Reduction Rating) The labeled attenuation of a hearing protector, in decibels, derived from laboratory measurement under [ANSI S3.19](https://webstore.ansi.org/). Real‑world attenuation is typically lower than the labeled NRR; OSHA recommends derating foam plug NRR by 50 % and muff NRR by 25 % for practical exposure calculations. Modern fit‑testing systems measure attenuation in the user's actual ear. ## O ### OSHA PEL (Permissible Exposure Limit) OSHA's regulated occupational noise exposure limit: **90 dBA over an 8‑hour TWA, with a 5 dB exchange rate**. Codified at 29 CFR 1910.95; unchanged since 1983. Hearing‑conservation programs are mandatory at the 85 dBA action level. See [workplace standards](/workplace). ## P ### Pascal (Pa) The SI unit of pressure: one newton per square meter. Atmospheric pressure is about 101,325 Pa. The threshold of hearing is about 20 µPa (0.00002 Pa). The threshold of pain is about 20 Pa. ### Phon A unit of loudness level defined as the SPL of a 1 kHz tone perceived as equally loud as the test tone. A 60 phon tone at any frequency sounds as loud as a 60 dB SPL tone at 1 kHz. Distinct from the **sone**, which measures perceived loudness on a linear scale. ## R ### Reverberation time (RT60) The time it takes for sound in a room to decay by 60 dB after the source stops. Standardized as **RT60**. Lower reverberation time improves speech intelligibility; ANSI S12.60 recommends 0.6 s RT60 for classrooms. Living rooms typically have 0.3 – 0.6 s; cathedrals can exceed 5 s. ## S ### Sone A linear unit of perceived loudness. 1 sone = 40 phon (a 40 dB SPL tone at 1 kHz); 2 sones = 50 phon (twice as loud); 4 sones = 60 phon. Used in equipment loudness specifications (HVAC, kitchen appliances) where a perceptually linear measure is more useful than the logarithmic dB. ### Sound Pressure Level (SPL) The decibel value of a sound pressure measurement, referenced to 20 µPa. Always reported in dB; usually further qualified by weighting (dBA / dBC / dBZ) and time weighting (Fast / Slow / Impulse). ### STS (Standard Threshold Shift) A change in audiometric thresholds of an average of 10 dB or more at 2, 3, and 4 kHz, measured against a baseline audiogram. STS is a trigger for required follow‑up under OSHA's hearing‑conservation program: refit hearing protection, retest, consider removing the worker from the high‑noise area. ## T ### Threshold of hearing The lowest sound pressure level a healthy young human ear can detect at a given frequency. Defined by convention as **0 dB SPL at 1 kHz** (corresponding to 20 µPa pressure). Higher (less sensitive) at very low and very high frequencies — see equal‑loudness contour. ### Time weighting (Fast / Slow / Impulse) Exponential averaging applied to the squared pressure signal before computing the SPL display. **Fast** uses a 125 ms time constant — the default for most measurements. **Slow** uses 1 s — for steady ambient. **Impulse** uses 35 ms attack and 1500 ms decay — for transient events. ### Tinnitus The perception of sound (ringing, buzzing, whining) in the absence of an external source. Often follows acoustic exposure; chronic tinnitus is associated with measurable hearing loss in most cases. The CDC estimates 50 million Americans live with tinnitus. ### TWA (Time‑Weighted Average) The 8‑hour energy‑equivalent of a worker's variable noise exposure during a shift. Calculated from dose: `TWA = 16.61 × log10(D/100) + 90` under OSHA's 5 dB exchange rate, or `TWA = 10 × log10(D/100) + 85` under NIOSH's 3 dB rate. The compliance‑relevant quantity in every occupational noise standard. ## Z ### Z‑weighting (zero / flat) A flat frequency response across 10 Hz to 20 kHz. Replaces the older "linear" or "unweighted" terminology, which was inconsistent across manufacturers. Used for research, instrument verification, and any measurement where weighting would add unwanted distortion. Defined in IEC 61672‑1. --- If a term you're looking for isn't here, it is likely either covered on the [science page](/science) (technical concepts) or the [hearing health page](/health) (medical and physiological concepts). The [comparison chart](/comparison) ties many of these terms back to real‑world sound levels. # Frequently Asked Questions: Sound Decibel Meter These are the questions we get most often about the [browser decibel meter](/) on this site, the underlying acoustics, and what the readings mean for everyday hearing decisions. Each answer is short and self‑contained; deeper coverage on any topic is one click away in the linked page. ## How accurate is this online decibel meter? Out of the box, a phone or laptop microphone running our meter is typically off by **5 to 15 dB** from a calibrated Class 2 sound‑level meter. After a one‑time [calibration procedure](/calibration), the agreement is usually within **±2 dB** for steady mid‑range sources (40 – 95 dBA) — close enough for personal exposure tracking and most non‑compliance use cases. For formal compliance — OSHA inspections, workers' compensation, noise‑complaint cases — a calibrated Class 2 SLM (IEC 61672‑1) is required. Browser meters are not certifiable as compliance instruments, no matter how carefully they're calibrated. [Learn more →](/calibration) ## Why does the meter need microphone permission? A sound‑level meter, by definition, has to listen to the sound. The browser's `getUserMedia` permission is the standard mechanism for any web page to access the microphone, and it requires explicit user consent the first time. Permission is requested only when you click _Start_, and is automatically released when you close the tab. If your browser blocks the prompt or the microphone is denied, the meter cannot function. There is no workaround on our side that wouldn't also defeat the security model the browser is enforcing. ## Does the meter record or upload my audio? No. All audio processing happens **locally in your browser**, in JavaScript and the Web Audio API. No audio samples, FFT frames, derived levels, or any other audio‑adjacent data are transmitted to any server. The site has no audio analytics endpoints because it has no server‑side audio handling at all. You can verify this in your browser's network tab while the meter is running — there is no traffic during measurement, only static asset loads at page open. ## What's the measurement range? Software‑side, the meter handles signals from approximately **25 dB SPL to 130 dB SPL**. Hardware‑side, most consumer phone and laptop microphones **clip between 95 and 110 dB SPL** because they are designed for voice calls, not for high‑level acoustic measurement. Above the clipping point, the meter under‑reports the actual level. For loud sources — concerts, sports events, machinery — readings up to about 95 dBA are reliable on most devices. Above that, expect under‑reading until you reach a Class 2 SLM rated to 130 dB or more. [Learn more →](/calibration#what-you-cannot-calibrate-around) ## Does it work on iPhone, Android, and tablets? Yes. The meter runs on iOS Safari, Android Chrome, and the desktop versions of Chrome, Firefox, Safari, Edge, and Brave. iOS Safari specifically suspends Web Audio when the tab is backgrounded for more than a few seconds, so leave the tab in the foreground for long measurements. Microphone gain varies dramatically across devices. A phone that reads 65 dBA in a quiet office may read 75 dBA on the next phone in the same room. This is hardware variability, not a bug. Set the [calibration offset](/calibration) per device. ## Why are my readings different from a friend's phone? Two phones in the same room can disagree by 5 – 15 dB before calibration. Causes: - **Different microphone sensitivity** at the factory. MEMS mics are spec'd to ±3 dB tolerance, and devices vary further by mounting and housing acoustics. - **Different audio pipelines.** Some platforms apply more aggressive noise suppression and AGC than others, changing the relationship between SPL and digital sample value. - **Different microphone positions** in the housing. A bottom‑mounted mic reads differently than a top‑mounted one when the device is flat on a desk. After calibrating both devices once, the readings should agree within 1 – 2 dB on the same source. Without calibration, large disagreements are normal. ## Can I use this meter for OSHA or workplace compliance? Not directly. OSHA 29 CFR 1910.95 and EU Directive 2003/10/EC require measurements made with a calibrated Class 1 or Class 2 sound‑level meter (IEC 61672‑1) and, for variable‑exposure workers, personal noise dosimetry (ANSI S1.25). A browser meter is not certifiable as either. What you **can** use a browser meter for, professionally: - **Initial walk‑through screening** to identify whether a formal survey is needed. - **Spot‑checking** suspected hotspots between formal surveys. - **Worker self‑awareness** of their typical exposure environment. If two or more locations exceed 85 dBA on screening, you have a hearing‑conservation obligation that a Class 2 SLM survey is needed to document. [Learn more →](/workplace) ## How do I calibrate my device? Run a side‑by‑side comparison with a known reference. The simplest method: 1. Place your phone or laptop next to a calibrated Class 2 SLM in a space with steady mid‑range noise (a fan or HVAC duct at 60 – 80 dBA works well). 2. Match the settings — A‑weighted, Slow time weighting, on both. 3. Average each meter's reading for 30 – 60 seconds. 4. Subtract: **reference reading − your reading = offset**. 5. Enter the offset in our meter's settings. If you don't have access to a reference SLM, anchoring against a known quiet space (a bedroom at night is typically 30 – 35 dBA) gets the calibration into the right ballpark. [Learn more →](/calibration) ## What's the difference between dB SPL and dB FS? **dB SPL** (sound pressure level) is the physical decibel scale used for acoustic measurements, referenced to 20 µPa of air pressure variation. Every published noise number — NIOSH, OSHA, WHO, [the comparison chart on this site](/comparison) — is dB SPL. **dB FS** (decibel full scale) is a digital‑audio scale where 0 dB FS is the maximum representable digital sample value. Used in DAWs and audio production. Cannot be directly compared to dB SPL without a reference calibration mapping a known SPL to a known sample value. For nearly all use, leave the meter on dB SPL. ## What does A‑weighting (dBA) mean? A‑weighting is a frequency filter applied before the level is computed, designed to approximate how human ears respond at moderate listening levels. It heavily attenuates low frequencies (about −30 dB at 50 Hz) and slightly attenuates above 6 kHz. Almost every regulatory threshold — NIOSH 85 dBA, OSHA 90 dBA, WHO 30 dBA bedroom limit — is specified in dBA. If your meter reports plain "dB," it is most likely already A‑weighted; if not, A is the default to use. [Learn more →](/science#frequency-weightings) ## Why are my readings stuck at 0 dB or extremely low? Most likely causes: - **Hardware mute.** Many laptops have a physical mic kill switch. Check the F‑row keys. - **Wrong input device.** If a Bluetooth headset or USB mic is connected, the OS may have routed input there. Disconnect or change the system input. - **Permission denied.** The mic permission was denied or revoked for the site. Click the lock icon in the address bar and reset. - **Browser policy.** Some embedded webviews and corporate networks block `getUserMedia`. Try a personal device. ## Why are my readings unstable or fluctuating wildly? Almost always handling noise — the meter is responding to taps, rubbing, and movement of the device, not to the room sound. Place the device on a folded soft cloth and don't touch it during the measurement. For outdoor measurements, wind on the microphone produces 60 – 80 dBA of false reading; use a foam windscreen. [Learn more →](/tips#eliminating-contamination) ## Can I export the measurement data? Not in the current version. Data export — CSV, PDF report, timestamped log — is on the roadmap and is one of the differentiators from the competing tools that don't offer it. If this is something you'd use, it's a feature we're prioritizing for the next release. ## Does the meter work offline? After the first page load over HTTPS, the static assets (HTML, CSS, JavaScript) are cached by your browser and the meter runs without a network connection. The microphone API is browser‑local; nothing about the meter requires network access during measurement. The site does not currently install as a Progressive Web App, so opening the meter from a fresh browser session does require an initial network fetch. ## Is the source code open? Not at this time. The codebase is planned to be open‑sourced once the core features stabilize. Until then, the technical pages on this site ([science](/science), [calibration](/calibration), [tips](/tips)) are intended as the authoritative reference for what the meter is doing internally. ## How does this compare to a dedicated app? A dedicated app (the iOS App Store and Google Play have several) can do things a browser cannot: run in the background, post notifications, log to a file, integrate with HealthKit, persist between sessions without browser cache. A browser meter, in exchange, requires no install, runs on any device with a microphone, doesn't need updates, and doesn't read or write any data outside the page itself. For a one‑off measurement or to introduce someone to the concepts, the browser is faster. For long‑term continuous logging on a single device, a dedicated app is more capable. ## What's the difference between this and a "professional" sound level meter? A professional Class 2 sound‑level meter (IEC 61672‑1) has: - A calibrated reference microphone with traceable certification. - Hardware that does not clip below 130 dB SPL. - Built‑in 1/3‑octave band analysis. - Built‑in Leq, Lmax, Lpeak integration. - A factory‑calibrated, tamper‑proof time base. - Documentation that holds up to regulatory inspection. Our browser meter has none of those. It is, however, **free**, **immediate**, and **good enough** for personal exposure awareness, informal measurement, and screening surveys before deciding whether to engage a Class 2 instrument. Choose the right tool for the question you're trying to answer. --- If your question isn't here, the rest of the site likely covers it: the [user guide](/guide) for how to operate the meter, the [calibration](/calibration) and [tips](/tips) pages for measurement practice, the [comparison chart](/comparison) for what numbers look like in real life, and the [hearing health page](/health) for what to do with the readings. # About Sound Decibel Meter Sound Decibel Meter is a free, browser‑based sound‑level meter built to make professional‑grade noise measurement universally accessible. No account, no install, no advertising, no audio leaving your device. The core meter, the reference content, and every page on this site are designed for one purpose: to help you measure the noise in your life accurately, understand what the numbers mean, and act on them. This page covers what the project is, why it exists, how it differs from similar tools, and how we approach privacy and data handling. If you want to know what the meter can do or how to use it, the [user guide](/guide) is the right starting point. ## Mission Hearing loss is one of the most common preventable health conditions in the world. The [World Health Organization](https://www.who.int/news-room/fact-sheets/detail/deafness-and-hearing-loss) estimates that over **1.5 billion people** live with some degree of hearing loss, with about a third of cases attributable to noise exposure that could have been avoided with awareness, measurement, and appropriate protection. The instruments that measure noise — Class 1 and Class 2 sound‑level meters certified to IEC 61672‑1 — are professional tools. They cost hundreds to thousands of dollars, require calibration discipline, and sit firmly outside the budget and patience of most people who would benefit from one. Modern smartphones have all the hardware needed to do useful sound measurement: a microphone, an ADC, enough compute to apply A‑weighting and FFT analysis in real time. What's been missing is a **well‑designed, multilingual, free** browser interface that turns that hardware into a meter without asking the user to install anything, create an account, or accept tracking. That gap is what this project fills. ## How we got here The decibel‑meter web app market is small but real — a handful of sites compete for the same set of search queries. The leading competitor in English is decibelmeter.org, an excellent product built by a small independent team using a similar technical stack. Its existence proves the demand. What it doesn't do is serve the **non‑English‑speaking** majority of the world: the WHO estimates that nearly half of all people living with noise‑induced hearing loss are in Asia, where the dominant search languages are Chinese, Hindi, Indonesian, and Vietnamese — none of which the existing tools fully serve. We started this project to close that gap. The meter itself is a re‑implementation in modern Next.js with React 19, optimized for mobile and desktop equally, with all the analysis on‑device. The content matrix is parallel: English first, then a planned 30‑language expansion with original (not machine‑translated) content for each target market. ## What we do differently Tools in this space tend to converge on the same feature set, so it's worth being explicit about the differences: ### Multilingual depth We treat translation as a content problem, not a localization problem. The technical documentation on the [science page](/science), [health page](/health), and [workplace page](/workplace) is rewritten in each target language by a native speaker familiar with the domain — not run through a machine translator and lightly edited. The [reference comparison chart](/comparison) is adapted to local references where appropriate (a "subway train" reference is more useful in Tokyo than in rural Wyoming). ### Community noise framing US‑based competitors lean heavily on OSHA and the 85 dBA / 90 dBA occupational framing because that's the regulatory framework most of their audience operates under. For readers outside the US, the more relevant framework is the [WHO Environmental Noise Guidelines](https://www.who.int/europe/publications/i/item/9789289053563) (community noise) and the **EU Directive 2003/10/EC** (occupational, with a stricter 85 dBA action value and 87 dBA exposure limit enforced at the ear). We cite all three frameworks throughout, and let readers see the actual numerical differences rather than defaulting to whichever standard is most familiar to the page author. ### Browser‑first, install‑optional The full functionality of the meter — calibration, weighting, spectrum analysis, reference matching, statistics — is in the browser, not in a paid app. There is no premium tier. There is no "upgrade for advanced features" button. The site is supported by modest affiliate links to third‑party hearing protection on pages where they're contextually relevant ([health](/health), [use cases](/use-cases)) — disclosed clearly on each page where they appear. We do not run display ads, and we do not have an audio analytics product. ### Honest limits Browser meters are not laboratory instruments, and we don't pretend otherwise. The [calibration page](/calibration), the [FAQ](/faq), and the [tips page](/tips) all explicitly cover where a phone meter is and isn't reliable: the clipping ceiling around 95 – 110 dBA, the non‑flat frequency response of consumer microphones, the fact that it's not a Class 2 instrument and shouldn't be used as one. Knowing the limits is what makes the readings trustworthy within them. ## Privacy Privacy is structural, not promised: - **All audio processing happens in your browser.** Microphone audio is routed through the [Web Audio API](https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_API) to a JavaScript analyzer in the page. No audio samples, FFT frames, derived levels, or any other audio‑adjacent data are ever sent to a server. This is a property of how the page is built, not a policy we promise to follow — open the network tab during a measurement and you can verify it yourself. - **No account required.** No email, no password, no profile. The meter works the same for everyone. - **Local persistence only.** Your calibration offset, language preference, and theme are stored in your browser's local storage for the site origin. Clearing site data clears them. - **No third‑party trackers in the meter session.** We use minimal privacy‑respecting analytics (page views, geographic country at the city level, no fingerprinting) on content pages, and **none** on the meter page during a measurement session. Full details are in the [privacy policy](/privacy-policy). ## Standards we follow The meter implements behavior consistent with the relevant international standards: - **A, C, and Z weighting** per [IEC 61672‑1](https://www.iec.ch/) — the international standard for sound‑level meter performance. - **Time weighting** (Fast 125 ms, Slow 1 s, Impulse 35/1500 ms) per IEC 61672‑1. - **Reference values** in the comparison chart and use‑case pages drawn from [NIOSH](https://www.cdc.gov/niosh/topics/noise/), [CDC](https://www.cdc.gov/nceh/hearing_loss/), [WHO](https://www.who.int/news-room/fact-sheets/detail/deafness-and-hearing-loss), [EPA](https://www.epa.gov/clean-air-act-overview/epa-history-noise-and-noise-control-act), and ISO 1996‑1/2. - **Hearing protection ratings** per [ANSI S3.19](https://webstore.ansi.org/) (NRR) where mentioned. The meter is **not** Class 1 or Class 2 certified — that designation requires hardware that consumer phones and laptops do not have, and formal traceable calibration that a browser cannot perform. It does, however, follow the same signal‑processing chain that a Class 2 meter follows, so its behavior is qualitatively comparable. ## Differentiation roadmap A few capabilities we're actively building toward: - **Data export** — CSV and PDF logs with timestamps, useful for formal documentation of long‑term exposure (noise‑complaint cases, rental disputes, cumulative occupational exposure). - **Per‑device calibration profiles** — named offsets for users who measure on multiple devices. - **Leq integration** — the energy‑equivalent continuous level over arbitrary windows, currently approximated by Avg. - **Native PWA install** — offline meter, home‑screen icon, no browser‑cache dependency. - **30+ language content** — beginning with the major Asian and Romance languages, expanding to cover the bulk of global search intent for sound‑measurement queries. If any of these matters to you specifically, we'd like to hear about it. See [contact](#contact) below. ## Contact The fastest way to reach us is by email at [hello@sounddecibelmeter.org](mailto:hello@sounddecibelmeter.org). We answer: - Bug reports (please include browser, device, OS version, and a reproduction). - Feature requests (especially from people in compliance, healthcare, music production, and education — the use cases that drive the roadmap). - Translation contributions and corrections (every page is open to feedback from native speakers). - Press, partnerships, and content collaborations. We don't currently have a public bug tracker; that's planned alongside open‑sourcing the codebase. Until then, email is the channel. ## Legal For the formal terms governing use of this site and the meter, see the [privacy policy](/privacy-policy) and the [terms of service](/terms-of-service). The short version: the meter is provided as‑is, without warranty, intended for personal and informational use, and explicitly not as a substitute for a calibrated sound‑level meter where one is required by law or by professional practice. # Privacy Policy _Last updated: 2026-05-01_ Sound Decibel Meter is operated at **sounddecibelmeter.org** (the "Site"). This page explains, in plain language, what data we handle, what we don't, and how the Site is built so you can verify it. The summary fits in three lines: - **Microphone audio never leaves your device.** All sound analysis is done locally in your browser; we have no audio endpoint and no audio storage. - **No account is required, ever.** We do not ask for an email, name, or password. - **We use minimal, aggregated analytics on the article pages only.** No fingerprinting, no advertising trackers, no third-party data brokers. The rest of this page is the long version, organised by category of data. ## What we collect ### Microphone audio We collect **none**. The browser sound meter on the [home page](/) requests microphone access via the standard [`getUserMedia`](https://developer.mozilla.org/en-US/docs/Web/API/MediaDevices/getUserMedia) API and processes the audio stream locally through the [Web Audio API](https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_API). The resulting decibel values are rendered on screen and discarded. No audio samples, FFT frames, derived levels, or any other audio-adjacent data are ever transmitted to a server. The Site has no audio analysis endpoint because there is no server-side audio processing whatsoever. You can verify this for yourself: open your browser's network panel during a measurement session and watch the traffic. You will see no requests after the page loads. When you close the tab, the microphone is released automatically. ### Local browser storage The Site uses your browser's `localStorage` to persist three small preferences across visits: - **Calibration offset** (a single signed dB value) — so you don't have to recalibrate every session. - **Theme** (`light` or `dark`). - **Language** (one of the supported locales). This data lives only on your device, scoped to the `sounddecibelmeter.org` origin. It is never transmitted to us. Clearing your browser's site data removes it. ### Analytics On the **article pages** (everything except the meter on the home page), we use a privacy-respecting analytics service to count aggregate visits. The fields we receive are: - Page URL (e.g., `/calibration`). - Referrer (the previous page you came from). - Approximate country (derived from IP at request time, then discarded). - Browser type and screen size (broad bucket). - Whether the visit is a first-time or returning view. We **do not** receive your IP address, device fingerprint, login state, or any identifier that would let us follow you across sites. The Site does not load advertising trackers, cross-site cookies, or social media pixels. We deliberately do not run analytics during a meter session on the home page, so meter use leaves no trace beyond the session itself. ### Cookies The Site sets one technical cookie used by the language router (`NEXT_LOCALE`) to remember your preferred locale. There are no advertising or tracking cookies. If your jurisdiction requires explicit cookie consent for analytics (EEA, UK, Switzerland, others), you can disable analytics in your browser's "Do Not Track" settings, via a content blocker, or by declining consent in the prompt your browser shows the first time it loads an analytics script. The meter itself works the same in either case. ### Affiliate links A small number of articles link to consumer hearing-protection products on third-party retailers (e.g., Amazon). Some of those links carry an affiliate tag — meaning the retailer pays us a small commission if you buy after clicking. This is the only commercial relationship the Site has. The affiliate retailer sees the click and may set their own cookies after you arrive on their domain; that data is governed by **their** privacy policy, not ours. We label affiliate links inline where they appear and never let commercial considerations alter the technical recommendations we publish. ### Email If you contact us at the address listed on the [Contact](/contact) page, we receive your email address and the message you send. We use it to reply, retain it for as long as needed to provide ongoing support, and then delete it. We do not add you to any mailing list and we do not share your address with third parties. ## What we do not collect To make this exhaustive: - We do not record, store, transcribe, or analyse audio from your microphone. - We do not read or write files on your device beyond `localStorage` as described above. - We do not collect health information, even though the Site discusses hearing health. - We do not collect location data beyond approximate country for analytics. - We do not run advertising networks, social-media trackers, retargeting pixels, or session replay tools. - We do not sell, rent, or share data with data brokers. ## Children The Site is intended for a general audience. We do not knowingly collect personal information from anyone under 13, and the meter itself is designed not to collect personal information from anyone of any age. Parents who notice anything that contradicts this can write to us and we will investigate. ## International transfers We are based in a single country and our analytics provider may store aggregate logs in a country different from yours. Because we do not collect personal data tied to identified individuals, this transfer carries minimal privacy risk. If you are an EEA, UK, or Swiss resident exercising rights under the GDPR or equivalent, see [Your rights](#your-rights) below. ## Your rights If you are in a jurisdiction with a comprehensive privacy law (EEA, UK, California, Brazil, others), you have rights of access, correction, deletion, portability, and objection. Because the Site holds essentially no personal data about you — no account, no audio, no profile — most of these rights resolve to "there is nothing to deliver or delete." If you have specifically emailed us and want your prior correspondence deleted, write to the [contact address](/contact) and we will action it within 30 days. The Site is not currently subject to a data protection authority register, since the categories of data we process do not require one. If a data protection regulator wishes to contact us, the contact email reaches a human within one business day. ## Changes to this policy If we change anything material, we will update the "Last updated" date at the top of this page and post a brief note on the [home page](/) for at least 30 days. Cosmetic edits (typos, link reformatting) are made without notice. ## Contact Questions about this policy or the data the Site handles: see the [Contact page](/contact). Plain English answers preferred, plain English answers given. # Terms of Service _Last updated: 2026-05-01_ These terms govern your use of **sounddecibelmeter.org** and its sub-pages (the "Site"), including the in-browser sound level meter and the article content. By using the Site, you agree to these terms. If you do not agree, please don't use the Site. The version in two lines: - The meter is a **screening tool**, not certified measurement equipment. Use it for personal awareness, not for compliance, litigation, or formal documentation. - The Site is provided **as-is**, with no warranty. You use it at your own risk. The rest of this page is the long version. ## What the Site provides The Site offers, free of charge: 1. A **browser-based sound level meter** that uses your device microphone, the Web Audio API, and on-device computation to display A-, C-, or Z-weighted sound pressure levels in dB SPL after you complete a one-time per-device calibration. 2. **Reference articles** on hearing health, noise-related occupational and environmental standards, measurement technique, and acoustics fundamentals. 3. A **glossary, FAQ, and per-locale translated content** covering 20 languages. The Site is operated by an independent team. We are not affiliated with NIOSH, OSHA, the WHO, IEC, ANSI, the EU Commission, or any of the standards bodies whose work we cite. References to those bodies are factual citations, not endorsements in either direction. ## Measurement accuracy disclaimer This is the most important section of these terms. The browser meter is **not a certified Class 1 or Class 2 sound level meter** as defined by IEC 61672-1, ANSI S1.4, or any equivalent standard. It is a screening tool that runs on consumer hardware (smartphone or laptop microphones) whose acoustic characteristics vary by ±3 dB at the microphone alone, plus additional variability from the audio pipeline. After calibration the readings are typically within ±2 dB of a Class 2 reference for stable mid-range sources between 25 and 95 dB SPL — adequate for personal use, **not** adequate for: - **Regulatory compliance** under OSHA 29 CFR 1910.95, the EU Physical Agents (Noise) Directive 2003/10/EC and its national transpositions, the UK Control of Noise at Work Regulations 2005, similar workplace-noise regimes in other jurisdictions, or any matter where a labelled Class 2 instrument is required by law. - **Legal proceedings** of any kind, including noise complaints, environmental enforcement, civil disputes between neighbours or landlords/tenants, and personal-injury or workers'-compensation claims. - **Medical or audiological assessment**, including hearing-loss diagnosis, hearing-aid fitting, or any clinical purpose. - **Measurement above approximately 95 dB SPL**, where most consumer microphones begin to clip and underreport the actual level. If you need readings that hold up in any of those contexts, use a calibrated Class 1 or Class 2 sound level meter (IEC 61672-1) operated by, or under the supervision of, a qualified industrial hygienist, audiologist, or acoustician. You should not, and you may not, hold us responsible for outcomes that depend on the Site's readings being more accurate than they actually are. ## No warranty The Site is provided "as is" and "as available", without warranty of any kind, whether express, implied, or statutory. We disclaim all warranties to the maximum extent permitted by applicable law, including warranties of merchantability, fitness for a particular purpose, accuracy of content, non-infringement, uninterrupted availability, freedom from defects or malware, and compatibility with any particular device, browser, or operating system. We do not warrant that the Site will be available without interruption, that defects will be corrected, that the content is current beyond the dates noted on each page, or that any specific reading or recommendation will produce a particular result for your situation. Browsers and operating systems change frequently, and a configuration that works today may behave differently after an update. ## Acceptable use You may use the Site for personal, educational, professional research, and journalistic purposes. You may quote short excerpts of article content in other works with attribution and a link back. You may link to any page on the Site without asking permission. You may **not**: - Use the Site to misrepresent measurements as having been produced by a certified instrument when they were not. - Scrape the Site at a rate that materially burdens our infrastructure (a normal browser-driven crawl is fine; aggressive automated scraping is not). - Reverse-engineer, decompile, or attempt to extract source code or API endpoints other than those exposed by the published HTML, CSS, and JavaScript of the Site itself, with the intent to operate a derivative service that masquerades as ours. - Use the Site in any way that violates applicable law, infringes third-party rights, or creates liability for us or our hosting provider. - Bypass technical measures the Site uses to enforce these terms or protect content licensed from third parties. ## Intellectual property Article text, charts, and other content authored by the Sound Decibel Meter team are © Sound Decibel Meter Team and licensed for personal and educational use under the same terms as the Site itself. Quotations from third-party standards (NIOSH, OSHA, ISO, IEC, WHO, EPA, ANSI, and similar bodies) remain the property of their respective publishers and are reproduced under the standard limits of fair use, fair dealing, or similar exceptions in your jurisdiction. The Site's source code, including the meter's signal-processing routines, is currently proprietary. We intend to open-source it on a permissive licence once the core feature set stabilises; this section will be updated when that happens. Brand names of third-party products mentioned in articles (e.g., Loop Experience 2, Etymotic ER‑20, 3M Peltor, Bose QC, Sony WH‑1000XM, and similar) are the trademarks of their respective owners. Their appearance is descriptive: we discuss them as examples of categories of hearing protection. No endorsement, affiliation, or sponsorship is implied unless we explicitly note one. ## Affiliate links Some article pages contain affiliate links to consumer hearing-protection products on third-party retailers. If you click through and make a purchase, the retailer may pay us a small commission at no extra cost to you. This is disclosed on each page where it applies and never affects the technical content of the article. ## Limitation of liability To the maximum extent permitted by applicable law, in no event shall the Sound Decibel Meter team, its operators, or its content contributors be liable for any indirect, incidental, special, consequential, or punitive damages, or any loss of profits or revenues, whether incurred directly or indirectly, or any loss of data, use, goodwill, or other intangible losses, resulting from: - Your access to, use of, or inability to access or use the Site; - Any decision you make on the basis of measurements taken with the meter or content read on the Site; - Any unauthorised access to or alteration of your transmissions or data; or - Any other matter relating to the Site. In jurisdictions that do not allow the exclusion of certain warranties or the limitation of liability for incidental or consequential damages, the above exclusions and limitations may not apply to you. In those jurisdictions, our liability shall be limited to the maximum extent permitted by law. If, despite the foregoing, we are found to be liable for any matter relating to the Site, our aggregate liability shall not exceed **EUR 100** (or the equivalent in your local currency at the time the cause of action arose). ## Indemnification You agree to defend, indemnify, and hold harmless the Sound Decibel Meter team from any claim, demand, loss, or damage, including reasonable legal fees, made by a third party that arises from your misuse of the Site, your violation of these terms, or your violation of applicable law or third-party rights. ## Termination We may suspend or restrict access to the Site, in whole or in part, at any time and for any reason, with or without notice. We may also remove or modify content at our discretion. The disclaimers, limitations of liability, and intellectual property terms above survive any termination. You can stop using the Site at any time by closing the tab. ## Governing law These terms are governed by the laws of the European Union and, where EU law leaves room, the laws of the country in which the Site's primary operator is established. If a dispute arises that cannot be resolved by direct correspondence, the courts of that country shall have non-exclusive jurisdiction. Nothing in this clause prevents a consumer from bringing a claim in the courts of their country of residence as permitted by mandatory consumer-protection rules. ## Changes to these terms If we change anything material in these terms, we will update the "Last updated" date and post a brief note on the [home page](/) for at least 30 days. Continued use of the Site after a material change constitutes acceptance of the revised terms. If you don't accept a change, stop using the Site. ## Contact Questions about these terms, takedown requests, regulator inquiries, or anything else legal: see the [Contact page](/contact). We are a small team and aim to reply within five business days. # Contact us The fastest way to reach the Sound Decibel Meter team is **email**: [hello@sounddecibelmeter.org](mailto:hello@sounddecibelmeter.org) We answer in plain English from a real human inbox. There is no ticket queue and no phone tree. ## What you can write to us about - **Bug reports.** Please include the browser (Chrome, Firefox, Safari, Edge, Brave), the operating system and version, the device (smartphone model, laptop, desktop), and the steps to reproduce. A 30-second screen recording or a network-tab screenshot is gold. - **Feature requests.** We're particularly interested in requests from people doing professional measurement work — industrial hygiene, audiology, music production, building acoustics, school administration. Use cases that come from a real workflow shape the roadmap more than abstract ideas. - **Translation contributions and corrections.** Each article page is open to feedback from native speakers. If a sentence in your language reads as a stiff direct translation, tell us how it should read instead. We rewrite, not just patch. - **Press, partnerships, and content collaborations.** Yes to interviews, syndication of specific articles with attribution, and joint content with hearing-health professionals or accessibility organisations. Polite no to "guest post" pitches that are link-building disguised as collaboration. - **Affiliate questions.** We disclose affiliate links inline; if you spot one we missed, write and we'll fix it. - **Legal, takedown, and regulator inquiries.** We respond within five business days. For an urgent matter (a published article causing measurable harm), mark the email subject **URGENT** and we'll triage same-day during business hours. ## What we don't have (yet) - **No public bug tracker.** It's on the roadmap together with the open-source release of the codebase. Until then, email is the only channel and we keep an internal list. - **No support phone line.** We are a small team scattered across time zones; synchronous support would be a worse experience than written replies that we can deliver carefully. - **No data subject portal.** The Site holds essentially no personal data about you (see the [Privacy Policy](/privacy-policy) for the exhaustive list). If you want a copy of, or deletion of, prior correspondence with us, just ask in plain language and we'll action it within 30 days. ## Response times We aim to reply to every legitimate email within **two business days**. Translation and content corrections often get a same-day acknowledgement. Press and partnership emails may take longer when we're working out details internally; we will at least acknowledge receipt within two days. If you don't hear back within a week, your message may have been caught by a spam filter — feel free to follow up. ## Mailing address We don't list a mailing address publicly because we are a distributed team and there is nothing that physically arrives at "the office". If you need a postal address for legal service or regulator correspondence, write to the email above and we will provide one. ## Anything else If your question is one we hear often, the [FAQ](/faq) probably already answers it. If you want to know what the Site does and why, the [About page](/about) is the longer version. Thank you for using Sound Decibel Meter. The shortest version of our mission is: free, accurate enough, and honest about its limits — and emails from readers are how we keep it that way.