Threshold shifts in chinchillas exposed to low‐frequency noise for nine days

Abstract

At the end of a three‐day exposure to octave‐band noise centered at 63 Hz at an octave‐band level of 120 dB, chinchillas showed large temporary, and moderate permanent threshold shifts at 2000 Hz and only a moderate temporary shift at 90 Hz [Burdick et al., J. Acoust. Soc. Am. 61, S78(A) (1977)]. This was in contrast to the usual finding of maximum shift one‐half to one octave above the center frequency of the exposure band. Only the half‐octave frequency of 90 Hz was monitored during exposure. Consequently, nothing was known about the pattern of growth of the high‐frequency shift. Also, it did not appear that the shift at 90 Hz reached asymptote as has been found for higher‐frequency exposure bands. In the present study the exposure durations were increased to nine days and the growth of threshold shift at both 90 and 2000 Hz was monitored. Results confirm the high‐frequency effect found previously and indicate that the shift at 90 Hz did not reach asymptote after nine days.