Sound pressure weightings — dBA, dBC and dBZ
SPL alone is not enough. The weighting curve determines whether a reading is comparable to a regulatory limit.
Sound level meters apply frequency weightings to match the ear's response or to preserve specific spectral content. dBA is the OSHA/EU workplace standard; dBC is used for peak-impulse noise; dBZ (unweighted) is used in acoustics research.
The three weightings
A-weighting: mimics human ear at moderate SPL (~40 phon). Roll-off below 500 Hz. > C-weighting: nearly flat 30 Hz–8 kHz. Used for peak/impulse. > Z-weighting: flat 10 Hz–20 kHz. Research use.
Where each is used
dBA: OSHA 8-hour TWA (90 dBA action level), EU workplace directive, environmental noise. dBC: firearm and impact noise, peak SPL limits (140 dBC). dBZ: precise acoustic measurement, room mode analysis.
Worked example — factory hearing conservation
Compressor room: 92 dBA continuous, 100 dBC peak from a stamping press. The 92 dBA drives 8-hour exposure limits; the 100 dBC would only matter above 140 dBC peak (regulatory ceiling). Report dBC alone and you understate the routine hearing damage risk.
Recap
dBA for workplace TWA. dBC for peaks. dBZ for physics.
Try the converters mentioned in this article
FAQ
Can I convert dBA to dBC?+
Only if you know the spectrum. There is no fixed offset — dBC – dBA can be 0 to 20 dB depending on frequency content.
Is 'dBSPL' a weighting?+
No — SPL is just the reference (20 µPa). It combines with weightings: dB(A) SPL, dB(C) SPL.
This article was written by The Turbo Unit Converter engineering desk (Applied metrology & engineering units) and last reviewed on 2026-07-07 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.