Hearing protector attenuation for impulse noise

Abstract

The study of the effectiveness of hearing protection for impulse noise pose several problems. Due to the transient nature of the noise, real-ear-at-threshold (REAT) data are not readily applicable since current impulse-noise criteria are based on either (1) peak pressure, some measure of impulse duration, and the number of impulses, or (2) total A-weighted energy. It is possible to measure the effect of an earmuff on these parameters by positioning a miniature transducer under the muff at the wearer's ear canal. An alternative arrangement which permits the study of both ear muffs and plugs involves the use of an acoustic test fixture. The test fixture must simulate those characteristics of the head and outer and middle ears that affect the attenuation of hearing protectors on real ears. These include the viscoelastic characteristics of the circumaural and intra-aural skin, the inertial properties of the head, the frequency response of the auditory canal, and the mechanisms of bone conduction and physiological masking. DCIEM has sponsored by contract the development of such a test fixture [C. Giguere et al., J. Acoust. Soc. Am. Suppl. 1 78, S5 (1985)]. Attenuation results with the test fixture compare reasonably well with REAT-derived data. Agreement between the two methods could be improved for earplugs if the thickness of the artificial intra-aural skin were reduced. On-going research is directed towards studying human intra-aural skin, and measuring the peak attenuation, waveform-duration increase, and linear and A-weighted energy reduction of protectors for short- and long-duration impulses.