dB(A) vs dB(C): When Each Matters in Everyday Noise
TL;DR: Use dB(A) for most everyday noise; add dB(C) when low-frequency or very loud sound is present (bass, machinery, live music) or when a standard specifies C-weighting.
A- vs C-weighting in one minute
dB(A) approximates hearing at moderate levels—less sensitive to very low/high frequencies—so it’s good for a single “how loud is it?” figure. dB(C) is flatter (especially in the low end), so it captures bass energy better and is used for very loud or bass-heavy sound.
When to use A- or C-weighting
- Home & office: Use dB(A) for appliances, fans, conversation, general comfort.
- Music & nightlife: Pair dB(C) with dB(A) to understand bass impact and to check limits that specify C-weighting.
- Industrial & tools: With heavy machinery or impulsive noise, log both A and C.
- Complaints & hums: Add dB(C). A-only readings can miss low-frequency issues.
Quick measurement tips
- Weighting: Verify A or C (don’t assume defaults).
- Time weighting: FAST (LAF/LCF) for changing sounds; SLOW for steadier sources; use Leq if available.
- Placement: Mic at arm’s length, away from reflective surfaces and clothing.
- Wind: Indoors close windows; outdoors use a windshield and avoid gusts.
- Calibration: Do a quick field-check if you have a calibrator; otherwise compare to a known source.
Common pitfalls
- A-only for bass-heavy noise: Add dB(C) or you may under-report the problem.
- Mixing metrics: Don’t compare dB(A) from one place with dB(C) from another.
- Relying on a single MAX: Pair MAX with Leq and notes about duration.
- Poor context: Record source, location, duration; a quick photo helps memory.
FAQ
Which do regulations use? Many community/office rules use dB(A). Music and some industrial codes include dB(C). Follow your local rule.
LAeq vs LCpeak? LAeq is time-averaged A-weighted energy; LCpeak is the highest instantaneous C-weighted value. Different questions, different metrics.
