Abstract
As part of a program for determining the effects of eardrum impedance on hearing aids, the frequency response of a KEMAR mannikin in a free field was measured using modified Zwislocki simulators. The modifications permitted the representation of approximately 80% of the impedance range exhibited by normal ears—one at the 10th percentile, one at the mean, and one at the 90th percentile. In one experiment with the simulators unoccluded, frequency response was essentially the same for all impedances except for an 8 dB maximum change at the earcanal resonant frequency. Subsequent experiments with the simulators occluded by earmold-type inserts showed differences in the frequency response up to 15 dB due to the eardrum impedance and up to 20 dB due to the diameter of the insert bore. Substantial low and midfrequency resonances which can amplify the sound field SPL by as much as 14 dB depending on the eardrum impedance are produced by such occlusions.
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