The cochlear and audiometric changes that occur after traumatic impulse noise exposure were studied. Chinchillas were exposed to 50 impulses of 155 dB peak sound pressure level and 1 msec A-duration. Hearing thresholds were measured before and after trauma (one half hour through 30 days). Animals were at 30 days, and their cochleas were analyzed using the surface preparation technique.
Audiometrically, all animals manifested large temporary threshold shifts (TTS, 30 to 70 dB) which recovered by 30 days; however, all animals had virtually complete losses of outer hair cells in the region 8 to 12 mm from the apex. These results question the practice of evaluating the state of the cochlea and the noxiousness of a noise on the basis of quiet threshold.
Henderson D, Hamernik RP, Sitler R. Audiometric and Anatomical Correlates of Impulse Noise Exposure. Arch Otolaryngol. 1974;99(1):62–66. doi:10.1001/archotol.1974.00780030066011