Hardware
TesterSound Level Meter
Measure sound levels and noise with live decibel meter. Monitor ambient noise, track dB levels, and get warnings for loud environments using your microphone.
Have feedback? Report bugs, suggest features, or share your thoughts — we read them allAbout Sound Level Meter
Measure environmental noise and sound levels with a professional decibel meter. Monitor ambient noise in real-time using your device's microphone, track maximum and average dB levels, and receive warnings when noise reaches potentially harmful levels. Perfect for measuring workplace noise, testing acoustic environments, or monitoring sound pollution.
- Press Start measuring to activate your microphone and begin measuring sound levels.
- Watch the analog meter needle move as sound levels change in your environment.
- Observe the color-coded badge showing current noise level classification.
- If sound exceeds 85 dB, you'll see a "Too loud!" warning indicating potential hearing risk.
- Monitor the history chart to see sound level fluctuations over time.
- View statistics showing maximum, average values, and measurement duration.
- Use the reference guide to understand different noise levels and their effects.
- Press Reset to clear all statistics and start fresh measurements.
Frequently Asked Questions
A sound level meter measures the sound pressure level (SPL) in your environment in decibels (dB). SPL is a logarithmic ratio of measured pressure to a reference pressure of 20 micropascals (the threshold of human hearing at 1 kHz). The microphone converts air-pressure variations into a voltage, the app squares and time-averages that signal, then converts to dB via 20 × log₁₀(p/p_ref). Phones typically report dB SPL with A-weighting (dBA), a frequency-response curve that mirrors human ear sensitivity and de-emphasizes very low and very high frequencies. C-weighting (dBC) is used for measuring peak impulse noise. The display range usually covers 30–120 dB, with anything above 85 dB considered hearing-damaging over time.
Phone microphones vary widely in calibration — two phones at the same desk can report numbers 10 dB apart for identical noise. Testing against a known reference (a friend playing a steady 1 kHz tone at a fixed volume, or a calibrated SPL meter app like NIOSH SLM) shows how trustworthy your phone is for occupational hearing safety, traffic noise complaints, or home theater tuning. Modern iPhones (post iPhone 7) and Pixels actually use multiple mics and software processing that has been independently validated to within ±2 dBA of professional meters, but older or third-party Android phones can drift 10–15 dBA. This tester also helps identify mic dust, broken aux ports, or buggy automatic gain control.
The standard unit is decibels of sound pressure level (dB SPL), referenced to 20 μPa. Variants include dBA (A-weighted, the most common for environmental noise), dBC (C-weighted, for peak impulses), and dBZ (unweighted, flat). Time-weighting matters too: 'Fast' uses a 125 ms integration window, 'Slow' uses 1 second, and 'Peak' captures instantaneous spikes. The numeric scale ranges from 0 dB (hearing threshold) to 120 dB (jet engine at 30 m), with 60 dB conversation, 85 dB heavy traffic, 100 dB chainsaw. Doubling the sound energy adds 3 dB; doubling perceived loudness adds about 10 dB. Hearing damage thresholds: 8 hours at 85 dBA is the OSHA limit; 1 hour at 94 dBA; 15 minutes at 100 dBA.
Smartphone microphones are highly directional, especially at high frequencies. Pointing the mic away from a noise source can drop the reading by 5–10 dB, while pointing the mic at a hard wall produces reflections that add 3–6 dB. Pocket noise (clothing rubbing the mic), wind noise (gusts hitting the port), and handling noise (touching the phone) all add 10–20 dB of artifact. Even breath from the user reading the screen can spike low frequencies. For consistent measurements, hold the phone at arm's length, point the bottom mic toward the source, avoid windy conditions, and let the reading stabilize for 5–10 seconds. The 'Slow' time-weighting setting smooths these short-term variations into a meaningful average.
A-weighting is a frequency-response filter that mimics human hearing sensitivity, attenuating frequencies below 1 kHz and above 6 kHz where our ears are less sensitive. The IEC 61672 standard defines the exact A-curve, derived from the inverse of the 40-phon equal-loudness contour. Almost all environmental noise regulations (OSHA, NIOSH, EU Environmental Noise Directive) and product noise specs (refrigerators, cars) use dBA because it correlates with perceived loudness and risk of hearing damage. Use C-weighting only for impulsive noise (gunshots, fireworks, machinery slams) where low frequencies matter, or Z-weighting for scientific frequency analysis. A meter reporting dBA on a low-frequency rumble may read much lower than dBC for the same physical pressure.
Yes, with caveats. A 2014 NIOSH study compared 130 smartphone SLM apps to a Type 1 reference meter and found iOS apps using the calibrated NIOSH SLM averaged within ±2 dBA across the 65–95 dBA range — comparable to a Type 2 (general-purpose) meter under ANSI S1.4. Android performance was wider due to MEMS mic variation across manufacturers. Modern phones use MEMS digital microphones (Knowles SPH0645, ST IMP34DT05) with -38 dBV/Pa sensitivity and 64 dB SNR, more than adequate for typical noise levels. Limitations: phone mics saturate above ~120 dB SPL (loud concerts), have rolling AGC that distorts steady readings, and lack the calibrated diffuse-field correction of a true Type 1 meter.
The Web Audio API combined with getUserMedia is used. After requesting microphone permission via navigator.mediaDevices.getUserMedia({audio: true}), the audio stream feeds into an AnalyserNode that returns time-domain or frequency-domain data at 44.1 or 48 kHz sample rate. JavaScript computes the RMS amplitude per analysis frame, applies an A-weighting filter (cascaded biquads), then converts to dB. For mobile compatibility, audio context must be resumed inside a user-gesture handler; iOS Safari requires explicit user interaction. The Permissions API tracks consent state. Note that browsers expose normalized audio values (-1 to +1), not calibrated voltage, so absolute dB SPL requires an external calibration step against a known sound source.
IEC 61672 (also published as ANSI S1.4) is the master standard, defining three meter classes: Type 1 (precision, ±0.7 dB tolerance) used for legal and scientific work, Type 2 (general purpose, ±1.5 dB) used by industrial hygienists, and Type 3 (survey, deprecated). The A-, C-, and Z-frequency weightings are specified in this standard. OSHA 1910.95 sets workplace permissible exposure limits (90 dBA TWA, 85 dBA action level), while NIOSH recommends 85 dBA TWA. The WHO's 2018 Environmental Noise Guidelines target ≤45 dB Lnight for residential sleep protection. Phone apps cannot legally claim Type 1 or Type 2 compliance without calibration documentation, but the NIOSH SLM iOS app comes closest, validated to ±2 dBA across the 65–95 dBA range against a B&K Type 1 reference.
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