Influence of outer ear resonant frequency on patterns of temporary threshold shift.

Noise-induced hearing loss following a broadband noise exposure has been characterized by a notch in the audiogram in the 3.0 to 6.0 kHz range. It has been postulated that loss of sensitivity in this frequency range is related to the primary resonant frequency of the external auditory meatus. In order to further explore this hypothesis, 31 normal-hearing subjects provided measurements of acoustic gain of the external ear and temporary threshold shift (TTS). Subjects completed sweep frequency Bekesy tracking procedures prior to and immediately following a 30-minute broadband noise exposure (95 dBA). The frequency maximally affected by the noise exposure (Max TTS) was correlated to primary resonant frequency of the outer ear (Max RF). A significant positive correlation between these two measures was identified. A 100 Hz difference in Max RF resulted in approximately a 140 Hz change in Max TTS. Thus, the external ear plays a significant role in the frequencies affected by a broadband noise exposure.