| Abstract: | Arguments in favor of a theoretically based damage-risk criterion (DRC) for intense noise G.R. Price, J. Acoust. Soc. Am. 69, 171-177 (1981); 66, 456-465 (1979); J. Acoust. Soc. Am. Suppl. 1 62, S95 (1977)] are further developed here to make a crucial prediction. Based on measured spectral differences, it was predicted that rifle impulses would cause permanent threshold shifts at approximately 9 dB lower peak pressures than cannon impulses. In contrast, DRCs in use in the world predict that the cannon would be more hazardous than the rifle by 7 to 10 dB. Electrophysiological measures of sensitivity were used in 38 cats (76 ears) which were exposed to 60 impulses, approximately 3 s apart, at various peak pressures, from either a rifle or a 105-mm Howitzer. Hearing changes were followed until recovery was complete (2 months). Permanent threshold shifts began at about 140 dB for rifle impulses and 150-155 dB for cannon impulses, confirming the prediction and supporting the contention that there is a spectrally dependent critical level for the ear at high intensities. Implications for present DRCs and future risk assessment schemes are discussed. |
