Honeywell Safety recently released this Hearing Safety Glossary highlighting many of the important aspects of Hearing Protection.

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A-Weighting

A filter applied to noise measurements, intended to replicate the frequency sensitivity of the human ear. The A-weighting is the most commonly-used weighting scale in hearing conservation programs, as it predicts quite well the damage risk of the ear. Sound level meters set to the A-weighting scale will filter out much of the low-frequency noise they measure, similar to the response of the human ear. Noise measurements made with the A-weighting scale are designated dBA. If A-weighted measurements are used to determine adequacy of hearing protection, OSHA instructions stipulate that a correction factor of 7 dB should be subtracted from the NRR of the hearing protector [as an error cushion for C-minus-A differences], then subtract the resulting lower NRR from the dBA noise measure to determine the protected noise level for the worker.

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