G. Richard Price
U.S. Army Res. Lab., Human Res. and Eng. Directorate, Aberdeen Proving Ground, MD 21005-5425
Research findings continue to challenge the adequacy of existing impulse noise standards while consensus on a better formulation remains elusive. It is generally accepted that frequency weighting (reducing contribution of low frequencies) would be appropriate for impulse noise standards. However, data now present standards with twin problems which are opposite in character. On the one hand, the ear can be destroyed by intense exposures containing little energy (less than 10 J/m[sup 2]) [Hamernik et al., J. Acoust. Soc. Am. 81, 1118--1129 (1987); Price and Wansack, J. Acoust. Soc. Am. 86, 2185--2191 (1989)]. Conversely, the ear can also tolerate immense amounts of energy at high intensities (>100 kJ/m[sup 2]) [Johnson and Paterson, Proc. 1992 Hearing Conserv. Conf. 103--106 (1992)]. A mathematical model of hearing hazard being developed [Price and Kalb, J. Acoust. Soc. Am. 90, 219--227 (1991)] promises to handle this complexity by incorporating a nonlinear stapes as well as middle ear muscle contractions into a hazard assessment, which is based on calculated basilar membrane displacements. Among other things, the model suggests that occasional exposure to intense impulses may be responsible for much of both occupational and nonoccupational noise-induced hearing loss.