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, 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.
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.
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 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.
How do I calibrate my device?
Run a side‑by‑side comparison with a known reference. The simplest method:
- 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).
- Match the settings — A‑weighted, Slow time weighting, on both.
- Average each meter's reading for 30 – 60 seconds.
- Subtract: reference reading − your reading = offset.
- 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.
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 — 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.
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.
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, calibration, 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 for how to operate the meter, the calibration and tips pages for measurement practice, the comparison chart for what numbers look like in real life, and the hearing health page for what to do with the readings.