Modeling the ear's response to intense impulses and the development of improved damage risk criteria.
Proceedings: 1992 hearing conservation conference, April 1-4, 1992. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, task order 91-37982, 1992 Apr; :93-96
The development of an improved hearing damage risk criteria (DRC) by modeling the ear's response to intense impulses was investigated. The model of the external and middle ears was conceived in an electroacoustic form that conformed with the physiological anatomy of the ear. The flow of energy could be followed from the free field sound pressure into the ear canal, through the middle ear, and into the cochlea to produce basilar membrane (BM) displacement. A position for an earmuff was available, in case it was necessary to use one. Menus in the program permitted 44 variables. Stapes suspension and the cochlea modeling details were presented. Hazard calculation was based on the number of BM flexions, their amplitudes, and width of membrane at that location. Upward displacements appeared to correlate best with damage. Once the free field waveform was selected from the available menu of waveforms, the model calculated the resulting stapes displacement and provided a display of the two waveforms. An exposure movie was used to correlate pressure history of the pulse in air, and enabled detection of that part of the pressure waveform that just preceded the effect. Fitting the hearing loss data indicated that maximum hazard for gunfire impulses was the mid cochlea, regardless of the spectral peak of the impulses. With data from cats, it was necessary to assume that the middle ear muscles were continuously active in awake animals. The possibility of using the model to rate DRCs was discussed in terms of the capability of computer input of waveforms, and the use of digitizing boards to produce a hazard meter. The author concludes that the model's capability of detecting the part of the waveform that produces the hazard enables the development of corrective action in the proper place.
Audiometry; Computers; Ear-protectors; Employee-exposure; Risk-analysis; Hearing-disorders; Laboratory-animals; Mathematical-models; Sensory-disorders; Noise-induced-hearing-loss; Wave-propagation
Proceedings: 1992 hearing conservation conference, April 1-4, 1992