Ear canal resonance and temporary threshold shift.

An investigation was made to determine if a relation exists between ear canal resonance and the characteristic 4‐kHz notch of noise‐induced hearing loss. In normal‐hearing subjects (N = 15), temporary threshold shifts (TTS) were induced in a free‐field situation under two different conditions: (1) with the ear canal in its normal configuration and (2) with the canal extended to approximately twice its normal length and terminated by an artificial pinna. Under condition (1) the typical 4‐kHz notch was observed. Under condition (2), the notch occurred at approximately 2 kHz, i.e., at one‐half the normal frequency. Although for equal exposure (in terms of sensation level) no difference in TTS magnitude was observed between the two conditions, subjects demonstrated consistently longer recovery times, i.e., shallower dB/log time slopes, with the canals extended. Results support the notion that the noise‐induced 4‐kHz notch is mainly related to the ear canal resonance. [Supported by NIH grants.]