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Experimental Studies of Impulse Noise.

Nilsson-OL; Grenner-J; Katbamna-BJ; Rydmarker-S; Dunn-DE
Basic and Applied Aspects of Noise-Induced Hearing Loss 1986:393-404
Female pigmented-guinea-pigs with melanotic eyes were exposed to noise of increasing energy levels in an anechoic chamber. The peak level was maintained at 131.5 decibels sound pressure level but the repetition rate varied. Comparisons were made with steady state noise exposures. The results verified the existence of a critical level of noise energy which constitutes a definite nonlinear change in the input/output function of noise induced threshold elevation. Impulse noise produced a threshold shift which differed from that produced by continuous steady state noise. It is suggested that different physiological mechanisms underlie the damage caused by impulse and continuous noise exposures. Great significance was attached to the changing of exposure time below the critical level of energy which proved to be more important than changes in intensity. The peak sound level was more important than the repetition rate as far as damage to the ear was concerned. A nonsignificant tendency toward higher damage induction was noted when the high frequency content of the impulse was increased as compared to impulses with low frequency content. The frequency sensitivity of the guinea-pig ear may be an important factor here. Also of importance are differences in decay time of each impulse. A ten fold increase of the B-duration significantly increased threshold. While these general conclusions may be valid for humans, the authors caution that the results can not be directly transferred regarding absolute values.
Noise-exposure; Laboratory-animals; Industrial-noise; Physiological-response; Hearing-loss; Acoustical-measurements; Sound-propagation; Hearing-threshold;
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Salvi-RJ; Henderson-D; Hamernik-RP; Colletti-V;
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Basic and Applied Aspects of Noise-Induced Hearing Loss