Decibels Explained

A decibel is ten times the log of a power ratio. Sound pressure level uses 20 µPa as zero, so 0 dB SPL is the threshold of hearing and 120 dB is painful.

+3 dB doubles acoustic power; +10 dB sounds about twice as loud; +6 dB doubles sound pressure. Two identical noise sources add 3 dB, not double the dB number.

A-weighting follows hearing at moderate levels and reduces bass; it is used for exposure limits. C-weighting is flatter and used for peaks and bass-heavy noise like music and machinery.

dBA vs dBC: which one should you use?

dBA reduces low frequencies the way hearing does at moderate levels, so it is used for hearing safety. dBC is flatter and includes bass, so it suits music, subwoofers and low-frequency noise. A large gap (dBC much higher than dBA) means the noise is bass-heavy.

1. Hold the phone at arm’s length, mic towards the source.
2. Avoid touching the case; disable noise reduction if possible.
3. Measure for at least 30 seconds and note the average.
4. Repeat in several spots.

Calibration step by step

What calibration can fix

A constant offset, not frequency response or AGC.

Option A: reference meter

Best: compare side by side with pink noise and set the offset.

Option B: known environment

Use a room or tone with a known level.

Option C: repeatable anchor

A fixed source at fixed distance to track changes, even if absolute values are uncertain.

Verify without over-trusting

Check at a second level; if it is off by more than 2 dB, distrust both.

Uncalibrated phone apps and web meters can be off by 5–10 dB; some calibrated iPhone apps came within ±2 dB in a 2014 NIOSH study. Web browsers cannot read the mic’s sensitivity, so treat readings as estimates.

Calibrating a phone meter

Place the phone next to a reference meter playing pink noise, read both and set the offset to match. Recheck at a second level.

Phone hardware

Built for voice, not noise

Phone mics are tuned for speech and limit loud levels.

iOS vs Android

iPhones use consistent hardware, so calibrated apps can be accurate; Android varies by model.

Automatic gain control

AGC compresses levels; browser meters disable it where possible.

Good for and bad for

Good for comparisons and trends; bad for legal evidence or very loud and very quiet sources.

Remove the case and watch your grip

Cases and fingers cover the mic port and alter readings.

• Decibel Meter

Your ears are not microphones

Hearing is non-linear and level-dependent; meters weight frequencies to approximate it.

When dBA and dBC differ

A large C–A gap means strong bass content.

Which weighting should you use?

dBA for hearing safety, dBC for bass and peak checks.

Neighbourhood noise complaints

Record dBA and dBC; bass noise often shows mostly in dBC.

Three-pass protocol

Baseline 60 s with the source off, 60 s with it on, optional 15 s close check.

Placement rules

Arm’s length, away from walls, same height each time, no case.

Why average 60 seconds

Short checks catch random peaks; a minute gives a stable figure.

Interpreting the result

A source must be roughly 10 dB above background to measure it cleanly.

NIOSH vs OSHA

NIOSH: 85 dBA for 8 h with 3 dB exchange; OSHA: 90 dBA with 5 dB exchange.

Think in daily dose buckets

Add up exposure across the day, not single events.

Distance is your first volume knob

Doubling distance from a point source lowers level by about 6 dB.

Use breaks strategically

Quiet breaks let the ears recover.

Protect the high-risk minutes

Wear earplugs for the loudest activities.

dBA: the hearing-based standard

A-weighting reduces bass and extreme treble like the ear at moderate levels.

When readings do not match

Weighting, time response and mic position explain most differences.

A low-frequency check

Measure a bass-heavy source in dBA and dBC; a big gap shows strong bass.

A simple demo with a spectrum view

Open the spectrum analyzer while playing music to see where energy sits.

Protecting your hearing

Distance, time limits and earplugs.

Home theatre and car audio

Use dBC for bass-heavy systems and short peaks.

Calibrate the offset at a realistic level

Calibrate near the level you plan to measure.

Three ways to calibrate

Reference meter, known environment or a repeatable anchor.

Why 3 dB matters

It doubles energy and halves safe time even though it sounds only slightly louder.

Decibels are logarithmic

Each 10 dB step is ten times the power.

Everyday sound levels

Whisper 30 dB, conversation 60 dB, traffic 80 dB, concert 105 dB, jet at 30 m 140 dB.

When loud becomes dangerous

From about 85 dBA over hours, and instantly above 120 dB.

1. Use the same device, position and height each time.
2. Keep the mic away from walls and your body.
3. Average over at least 60 seconds.
4. Take three passes and use the middle result.
5. If you have a reference meter, note the offset and apply it with the calibration setting.