Impact noise: the importance of level, duration, and repetition rate.
Henderson-D; Subramaniam-M; Gratton-MA; Saunders-SS
J Acoust Soc Am 1991 Mar; 89(3):1350-1357
Experiments were designed to evaluate the applicability of the equal energy hypothesis (EEH) to impulse noise exposures in a controlled laboratory setting. The study was carried out in two parts. Adult chinchillas were used in both parts of the study. Chinchillas were exposed to equal amounts of acoustic energy. The first study examined the effect of repetition rate and level. Groups of at least five animals were exposed to one of the repetition rates: 4/second, 1/second, and 1/4 seconds with peak pressures of 107 to 137 decibels (dB) sound pressure level. In the second experiment the total duration of exposure was constant for each group, 5 days, and the amount of energy was constant by trading the exposure level (107 to 137dB) and the repetition rate (4/second to 1/1024 seconds). Results indicate that hearing loss resulting from exposure to impact noise did not conform to the predictions of the EEH. The permanent threshold shift as well as the hair cell loss were more or less equal across the lower peak exposure levels. Both hearing loss and hair cell damage increased for exposures with higher peak levels. Hearing loss and cochlear damage were dependent on the rate of exposure. The amount of hearing loss and hair cell damage appears to depend on the interaction of several factors including peak level, rate, and the susceptibility of the animal.
NIOSH-Publication; NIOSH-Grant; Noise-exposure; Laboratory-animals; Impulse-noise; Ears; Hearing-impairment; Noise-induced-hearing-loss; Exposure-methods
Journal of the Acoustical Society of America
State University of New York, Buffalo, New York