dBA vs dBC: Which One Should You Use?

The 30-second answer

Your online decibel meter offers three weightings under Advanced Controls: dBA, dBC, and dBZ. dBA filters sound the way your ears hear at everyday volumes — turning down deep bass and extreme treble — so it matches perceived loudness and every health limit. dBC stays nearly flat and keeps the bass, so it shows the physical punch of loud, low-heavy sound. dBZ applies no filter at all: the raw signal.

Rule of thumb: default to dBA; add a dBC reading whenever bass could matter; quote both with the suffix every time ("62 dBA Leq, 60 s" plus "74 dBC"). A big C-minus-A gap is itself the finding — it proves low-frequency dominance no single number can show. The full filter reference is our dB vs dBA weighting guide, with dedicated live tools at the dBA meter, dBC meter, and Leq meter.

What weighting actually does — the filter analogy

Think of weighting as tinted glasses for sound. The microphone hears everything; the filter decides what counts. A-weighting dims the bass end hard (your ears barely register 50 Hz at quiet volumes) and slightly trims extreme treble, leaving speech frequencies (1–4 kHz) untouched. C-weighting is nearly clear glass — almost everything passes — with only the very lowest and highest edges dimmed. That is why the same concert can read 98 dBA and 108 dBC at the same spot: the bass the A-filter removed is still physically there.

The correction table: what each filter removes

Negative numbers are attenuation — how much that frequency is turned down before the dB number is computed. Read one row: at 63 Hz, A-weighting subtracts 26.2 dB while C-weighting subtracts only 0.8 dB. That 25 dB gap is why neighbour bass can feel enormous yet read "only" 48 dBA.

How to use this table while measuring: open the frequency analyzer and look at where your noise lives. Energy piled below 250 Hz means dBA will read far lower than dBC — expect a 10–25 dB gap and quote both. Energy centred on 1–4 kHz (speech, alarms, hiss) means A and C will nearly agree within 2 dB — dBA alone is fine.

Same sound, three numbers — worked examples

Three realistic sessions, each measured 60 seconds as Leq on the same phone. The pattern matters more than the exact digits: the C-minus-A gap tells you the frequency story.

Diagnostic rule: a gap under ~5 dB means mid/high-frequency sound (dBA tells the whole story). A gap of 10 dB or more means bass dominates — switch your decisions to include dBC, check the spectrum below 250 Hz, and never dismiss the complaint because "dBA is only 48". Bedroom and neighbour cases like these walk through fully in how to measure home noise and 10 everyday sounds.

Quick-reference chart: which setting for which job

Print-this-line version: people questions → dBA; bass questions → add dBC; physics questions → dBZ. Full exposure math lives in safe exposure limits and the noise exposure guide.

How to measure both correctly in 60 seconds

Place the phone at ear height where people actually are, mic pinhole uncovered, yourself silent. In the live meter, set A-weighting and Slow response, record 60 seconds, and note average/Leq plus maximum. Without moving the phone, switch to C-weighting, record another 60 seconds of the same sound, and note the same numbers. Log both lines with place, distance, and duration — for example "living room, 2 m from wall: 48 dBA Leq / 68 dBC Leq, 60 s each" — and export CSV or save to the Noise Journal.

Two technique notes from the measuring guide and phone-and-PC guide: keep the phone 30 cm off the wall for neighbour logs (pressed against it you measure vibration, not sound), and calibrate once per device — a stored offset applies to A, C, and Z together, so cross-weighting gaps stay meaningful. If two phones disagree by more than ~5 dB after calibration on the same sound, suspect a covered mic or hidden gain control before suspecting the weighting — see are apps accurate and what affects accuracy.

Five mistakes that make dBA lie

1. Quoting dBA for a bass problem. A subwoofer at "48 dBA" sounds harmless on paper and shakes the sofa in reality — the 20 dB C-minus-A gap is the real finding. 2. Dropping the suffix. "70 dB" is ambiguous; "70 dBA" is data. 3. Comparing A on one phone with C on another. Fix weighting, distance, and duration before comparing anything. 4. Using instants instead of Leq. One flickering peak proves nothing; a 30–60 second energy average is quotable — that is what the Leq meter is for. 5. Measuring once. Repeat from a second spot; agreement within a few dB means you can trust the picture.

Bottom line: dBA answers "how loud does it feel and is it risky?", dBC answers "how much low-frequency punch is really there?", and together they answer "what kind of noise is this?" Measure both, write both down, and decide with data — then check the result against the full decibel chart.

Reference tool only — not for legal, medical, occupational, or regulatory decisions.

Frequently asked questions

Should I use dBA or dBC?
Use dBA for almost everything — sleep, rooms, streets, offices, and hearing risk — because it matches perceived loudness and every exposure limit. Add a dBC reading whenever bass could matter, such as concerts, engines, subwoofers, or neighbour rumble.

Why is my dBC reading higher than my dBA reading?
Because your sound contains bass. A-weighting subtracts deep low frequencies (about 26 dB at 63 Hz) while C-weighting keeps them (under 1 dB), so bass-heavy sounds always read higher in dBC. A gap over 10 dB proves low-frequency dominance.

When should I use dBC instead of dBA?
Use dBC for loud bass-heavy sound — concerts, clubs, engines, machinery, construction — and for any neighbour bass log. Still record dBA alongside it, since hearing-risk limits are A-weighted and the pair diagnoses the sound better than either alone.

What is dBZ and do I need it?
dBZ is zero weighting: a flat, unfiltered measurement of raw sound pressure. Most everyday users do not need it — dBA matches loudness better. Use dBZ for engineering tests, equipment comparisons, or raw-physics questions.

Which weighting do noise laws and exposure limits use?
Almost all use dBA: the NIOSH 85 dBA 8-hour recommendation, OSHA and EU action values, and community noise rules are A-weighted. Some workplace peak limits use dBC (for example 140 dBC peaks), which is why loud venues log both.

Sources and further reading

• IEC 61672-1 — Electroacoustics: sound level meters, frequency weightings A, C, and Z (correction values used in Figure 1 and the table).
• NIOSH — Criteria for a Recommended Standard: Occupational Noise Exposure (85 dBA limit, 3 dB exchange rate).
• EU Physical Agents Directive 2003/10/EC — exposure action values at 80 and 85 dBA with peak provisions.
• WHO — Make Listening Safe / night-noise guidance (A-weighted community and sleep reference values).