Sound pressure distributions and resonances in the human ear canal in the presence of a measuring microphone

The effect of measuring microphones on the acoustic pressure distribution in ear canals has been studied analytically and experimentally up to 20 kHz using scaled model ear canals and real ear canals molded from cadavers. These pressure distributions are a function of frequency, microphone size, microphone location, and ear canal geometry. The presence of the microphone causes not only a localized disturbance of the sound field, producing an erroneous pressure measurement, but also disturbs the pressure distribution across the eardrum, beginning in the mid-frequency range. Furthermore, the measuring microphone as well as the nonuniform canal geometry in the vicinity of the eardrum cause the longitudinal resonances of the ear canal to become anharmonic. This anharmonicity is analytically predictable for canals of sufficient crossectional uniformity and with sufficiently well behaved, but not necessarily uniform, crossectional canal-geometry near the eardrum. [Work supported by NIH.]