NoiseGaugedB(A), dB(C) and dB(Z): which weighting to use
Use dB(A) for almost everything: it matches how people hear and it's what noise rules and hearing limits use. Use dB(C) when bass or low rumble matters, such as music through a wall or machinery. dB(Z) is the raw, unweighted level. Comparing A and C tells you how much of a noise is low-frequency.
Why sound meters weight frequencies
Our ears are less sensitive to low and very high pitches than to the middle range where speech sits. A deep 50 Hz hum and a 1,000 Hz tone with the same physical energy don't sound equally loud. A frequency weighting is a filter that adjusts the reading so the number reflects what matters for the job.
The three weightings
| What it does | Use it for | |
|---|---|---|
| dB(A) | Strongly reduces low frequencies (about −26 dB at 63 Hz, −16 dB at 125 Hz) and slightly the very high ones, like human hearing at moderate levels. | Everyday noise, hearing safety, noise complaints, traffic, offices, bedrooms. |
| dB(C) | Almost flat; only the extreme lows and highs are reduced (about −0.8 dB at 63 Hz). | Bass-heavy music, subwoofers, engines and machinery, and peak levels for hearing safety. |
| dB(Z) | Zero weighting: what the microphone picks up. | Technical checks, comparing with other unweighted readings. |
The A–C gap: a quick bass detector
Measure the same noise in dB(A) and dB(C). If C is only a few decibels higher, the sound is mostly mid and high pitched (voices, clatter). If C is 10 dB or more higher, there's a lot of low-frequency energy: bass music, a running engine, ventilation or a neighbor's subwoofer. Low-frequency noise travels through walls easily and is often what keeps people awake, even when the dB(A) reading looks modest.
Response time: Fast, Slow and Impulse
Sound levels jump around. The response time sets how quickly the reading follows:
- Fast (125 ms) follows changes quickly. Good default; matches most modern regulations.
- Slow (1 second) smooths the reading. Easier to read for steady noise like a fan or traffic.
- Impulse rises in 35 ms and falls over 1.5 seconds, so short bangs and claps show clearly. Rarely used in rules today.
Average, Leq, peak and L90
- Leq, the equivalent continuous level, is the energy average over a measurement. Loud moments weigh more than in a simple average. Most noise limits are written as Leq, usually LAeq (A-weighted).
- Peak is the highest instant pressure, normally C-weighted. Hearing safety rules typically cap it at 140 dB.
- L10 and L90 are the levels exceeded 10 % and 90 % of the time. L90 is the background; L10 shows the louder moments.
Which settings to pick
- Hearing safety or noise complaints: dB(A), Fast, and look at Leq.
- Bass from a neighbor or a club: measure in dB(C) as well, and note the A–C gap.
- Steady machine or fan noise: dB(A), Slow.
Phone microphones aren't certified sound level meters. Readings are estimates; see our terms.