Decibel Shield
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dBA vs dBC: what the weighting means
dBA applies the A-weighting filter, which discounts low and very high frequencies the way the ear does at moderate levels, and is what noise limits and exposure rules use. dBC applies C-weighting, nearly flat across the range, and is used for peak levels, hearing-protector calculations and bass-heavy sound. The same noise reads higher in dBC whenever it has low-frequency content.
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The correction values
Both weightings are defined in IEC 61672-1 (ANSI S1.4 in the United States). A-weighting subtracts heavily below 500 Hz; C-weighting only rolls off at the extremes.
| Frequency | 63 Hz | 125 Hz | 250 Hz | 500 Hz | 1 kHz | 2 kHz | 4 kHz | 8 kHz |
|---|---|---|---|---|---|---|---|---|
| A-weighting | −26.2 | −16.1 | −8.6 | −3.2 | 0 | +1.2 | +1.0 | −1.1 |
| C-weighting | −0.8 | −0.2 | 0 | 0 | 0 | −0.2 | −0.8 | −3.0 |
Sources: OSHA Technical Manual, Section III Chapter 5 (weighting networks and the 140 dB peak limit); NIOSH. The FAQ answers what dBA means in one paragraph.
Which one to use
- Exposure and limits: dBA. OSHA, NIOSH, city ordinances and product labels all state limits in dBA with slow response, because it tracks hearing risk from everyday noise.
- Peaks and impulses: dBC. OSHA sets a 140 dB peak ceiling for impulsive noise measured without A-weighting; gunshots and hammer blows are checked this way.
- Hearing protectors: both. The EPA noise reduction rating is applied to a C-weighted level. With only a dBA figure, OSHA subtracts 7 dB from the rating first.
- Low-frequency complaints: compare them. A dBC reading 15 dB or more above the dBA reading means the noise is mostly bass, which walls pass and A-weighted limits under-count.
Is dBA or dBC louder?
For the same sound dBC is equal or higher, never lower, because C-weighting keeps the low frequencies that A-weighting discounts. A subwoofer can read 20 dB higher in dBC than in dBA; a whistle reads about the same in both.
Which weighting does a phone decibel meter use?
Almost all use A-weighting, matching the scale limits and charts are written in. Our meter is A-weighted and reports slow response; the accuracy page explains the calibration behind the number.
What is dBZ or dB(lin)?
Z-weighting is zero weighting: a flat response with no correction at all, defined in IEC 61672-1 to replace the older unweighted or linear setting. It is used for octave-band analysis and laboratory work rather than exposure.
Why does OSHA use dBA for exposure but a plain peak for impulses?
Exposure risk follows the ear response, which A-weighting models. Very short impulses can damage hearing by peak pressure regardless of pitch, so the 140 dB ceiling is set on the unweighted or C-weighted peak.