How the Decibel Meter Works

1. Open the page and start measuring

Open the meter on the device you will measure with — phone, tablet or laptop with a current browser (Chrome, Edge, Firefox, Safari). Click “Start Measuring”. Nothing to install, no account.

Tip: on busy streets or in thin-walled flats, take one reading with windows open and one closed — the difference shows what facade and glazing achieve.

2. Allow microphone access — and re-enable if blocked

The browser asks for microphone permission — a privacy guarantee, not a warning. Without consent the tool hears nothing. If denied by accident, re-enable via the padlock icon in the address bar and reload.

Processing is fully local: sceptics can measure offline after loading — the tool needs no server connection.

3. What happens behind the scenes: Web Audio API, RMS and weighting

The Web Audio API delivers the microphone signal in short blocks. From these the tool computes RMS (close to perceived loudness), peak (key for bangs and impulses) and Leq — the energy-equivalent level over time that professionals use for noise assessment.

Plus frequency weightings: dBA (A-filter, mirrors hearing, standard for noise and hearing), dBC (flatter, keeps bass — useful for music and machinery) and dBZ (raw, unfiltered). Time weightings set inertia: Fast (125 ms) catches brief peaks, Slow (1 s) smooths, Impulse (35 ms) captures transients.

4. Position correctly: ear height, source, distance

Measure room noise where people sit or stand — on the table at ear height, not in the hand. Single sources (speakers, machines) are measured frontally at a defined distance, e.g. 1 metre. Comparisons only hold at identical position and distance.

Outdoor rule: each doubling of distance drops the level by about 6 dB. “70 dB at 1 m” is a measurement — “70 dB” alone is not.

5. Keep the mic clear and measure long enough

Most common error: hand or case covering the mic port — quickly costs 10 dB. Check case and grip, never measure from pocket or bag. And never talk while measuring: your voice adds 10–20 dB.

Durations: 30 seconds for steady sounds (ventilation, hum), 1–2 minutes for rooms and traffic, 10–15 minutes for neighbourhood noise with events. For exposure questions the whole period counts — the noise exposure guide explains the NIOSH rule (85 dB = 8 hours, every +3 dB halves the time).

6. Read the values: live, minimum, Leq, maximum, peak

Live shows the moment — good for walking the room. Minimum reveals background in quiet moments. Average and Leq describe typical load and are the quotable numbers. Maximum shows the loudest event, peak the instantaneous pressure of bangs.

Sanity check with the decibel chart: a room that feels like a library should read 30–40 dB, not 60. At 60 the mic is usually covered or auto-gain is active.

7. Calibrate for comparable numbers

Without calibration phones scatter by 5–10 dB. Whoever compares, calibrates: known reference signal (e.g. 94 dB calibrator or trusted second meter), own average over 30–60 seconds, enter reference minus reading as offset in the calibration dialog. Afterwards before-after and device changes are far more stable — without creating lab precision, honestly said.

8. Repeat, export, interpret

One measurement is a sample: second position, different time (traffic, neighbours and heating vary through the day), measurement after change (window closed, ventilation off) — only the difference tells the story. Sessions export as CSV or JSON or save to the Noise Journal.

And the framing: below 70 dBA relaxed, from 85 dBA sustained hearing risk, above 120 dB immediate danger. Concerts, rehearsal rooms and workshops demand protection — the tool shows when.