An appraisal of methods for estimating effectiveness of hearing protectors

The protection afforded by a hearing protector to a wearer, defined here as the reduction in A-weighted sound pressure level at the ear, varies between wearers and between noises. “Effective protection” of a protector in a given noise, defined as the value reached by a specified majority of wearers, may be estimated by various methods according to the amount of information available on the noise. These methods comprise the octave-band and numerous “single-number” ratings which attempt, in differing degrees, to allow for wearer- and noise-dependent variations. They are reviewed here together with their underlying assumptions. Attenuation data on individual wearers for seven protectors were used in conjuction with 100 noise spectra to test the validity of these assumptions and to calculate and compare the errors of each type of method. On the basis of these results it was concluded that the best single-number method, representing a practical compromise between accuracy and convenience, is one which generates a rating number to be subtracted from the C-weighted sound pressure level of the noise.