Threshold shifts in chinchillas exposed to octave bands of noise centered at 63 and 1000 Hz for three days

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Abstract
Audiograms were obtained on 8 binaural chinchillas trained on a shuttlebox avoidance procedure. Four of the animals were exposed to 3 successive levels of an octave band of noise centered at 63 Hz: 100 dB SPL [sound pressure level]), 110 dB SPL (84 dBA) and 120 dB SPL (94 dBA). The other 4 animals were also exposed to 3 successive levels of an octave band of noise centered at 1000 Hz: 75 dB SPL (75 dBA), 85 dB SPL (85 dBA), and 95 dB SPL (95 dBA). All exposure durations were 72 h. Little threshold shift (TS) resulted from the lower 2 exposure levels of the 63 Hz noise band. At the 120 dB exposure level, maximum TS of 43 dB occurred at 2000 Hz. Permanent threshold shifts (PTS) of 16 dB at 2000 Hz and 11 dB at 1400 Hz were found. Exposure to the 3 levels of the 1000 Hz noise band produced TS of 20, 45 and 61 dB at 1400 Hz. The 95 dB exposure level resulted in PTS of 6dB at 1400 Hz and 9 dB at 2000 Hz. The major results were the high-frequency hearing loss to a low-frequency noise and the fact that noise bands matched within 1 dBA were not equally hazardous as dictated by damage-risk criteria. The 63 Hz noise band produced nearly twice as much PTS as the 1000 Hz noise band.

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