A-Weighting

A loudness measurement that ignores the deep bass and extreme highs the way human ears naturally do.

The A-weighting filter passes the midrange untouched while cutting deep bass hard and extreme highs slightly, giving a dBA reading that tracks perceived loudness.

What it is

A meter filter that ignores deep bass and extreme treble to match how loud sound actually feels to human ears.

Key facts

dBA = decibels through the A-weighting filter; the unit on almost every venue and council noise limit.
A-weighting is flat (0 dB) at 1 kHz, the reference pitch the curve is anchored to; defined in standard IEC 61672.
Bass is cut hard: -19.1 dB at 100 Hz, -30.2 dB at 50 Hz, -50.5 dB at 20 Hz.
Highs are trimmed: -2.5 dB at 10 kHz, -9.3 dB at 20 kHz; small +1.3 dB boost near 2.5 kHz.
Human hearing ~20 Hz to 20,000 Hz; A-weighting throws away energy at both ends.
C-weighting (dBC) stays nearly flat, so it captures bass; dBC always reads higher than dBA on bass-heavy music.
A dBC minus dBA gap over ~15-20 dB warns of hidden sub/bass the dBA reading masks.
0 dB SPL = quietest audible sound (20 micropascals); pain threshold ~120-130 dB SPL.
+10 dB sounds about twice as loud; +6 dB = double the pressure; +3 dB = double the power.
Safe Work Australia limit: 85 dBA averaged over 8 hours (LAeq,8h); every +3 dB halves the safe time.

How it works

Sound enters the mic; the meter splits it into frequency bands.
The A-weighting filter turns DOWN the bass and extreme highs, leaves the 1 kHz midrange alone.
All the adjusted bands are added back into one single number.
That number is displayed as dBA, closer to perceived loudness than the raw level.
Set your meter or app to the 'A' setting to match council and venue limits.

Real examples

A council outdoor permit says 'max 65 dBA at the nearest residence' so you measure in dBA, not raw SPL.
Workplace noise: front-of-house averaging 100 dBA means earplugs and limited exposure time.
A subwoofer-heavy DJ set reads 95 dBA but 112 dBC; that 17 dB gap flags bass neighbours will feel through walls.
A quiet conversation is about 60 dBA; a chainsaw at the operator is about 110 dBA.
Phone SPL apps default to dBA so they line up with most noise regulations.

How it helps in live sound

Set your SPL meter/app to A-weighting AND 'Slow' response to match how council limits are written.
Log LAeq (time-averaged dBA) over the set, not just the peak; permits and Safe Work limits are averages.
Run a second reading in dBC; if dBC minus dBA exceeds ~15 dB, pull the subs or high-pass to tame hidden bass.
Measure at the boundary / nearest residence, not at FOH; distance and walls change the number a lot.
Keep crew under 85 dBA average over 8 hours or hand out earplugs (foam plugs give ~20-30 dB cut).
Note mic position and weighting in your log (e.g. '63 dBA Slow @ fence line') so it is defensible.

Everyday analogy

It is like a bouncer who waves through midrange voices at full volume but heavily quietens the deep rumble and ultrasonic hiss before counting the crowd, because your ears barely notice those anyway.

Watch out

Myth: dBA is 'the real loudness'. Truth: it deliberately under-reads bass, so heavy subs can blow past a felt-bass complaint while still 'passing' the dBA limit; check dBC too.

Fun fact

A-weighting was originally designed only for quiet sounds (~40 phon) but got used everywhere because it was simple, which is exactly why it under-counts the bass at loud concert levels.

Key takeaways

dBA = sound measured through the ear-mimicking A filter; the unit on nearly all noise limits.
Flat at 1 kHz, big cut to bass (-30 dB at 50 Hz), small cut to highs, tiny boost near 2.5 kHz.
Always set the meter to A-weighting to match council and venue rules.
dBC stays flat for bass; compare dBA vs dBC to catch hidden sub energy.
Safe limit 85 dBA over 8 hours; every +3 dB halves the safe time.