Abstract
Hearing at the speech frequency range can be improved by modifications of the external and middle ear at the cost of hearing loss at low and/or high frequencies, which are not important for speech recognition. Experiments using the model of the external ear proved that the increase of cavity volume of the external ear changed its resonant peak to lower frequency. Use of a ring in a model of the external ear also showed similar effects. These results showed that hearing could be improved at around 1kHz by 10-20dB. The effects of middle ear modifications were studied with fresh human temporal bones. Stainless steel microspheres placed on the umbo was observed under a microscope with strobe illumination, and the displacement of the umbo was measured using a video measuring system. Blockage of the aditus ad antrum improved the hearing at 2.8kHz by 5.4dB (mean). Decrease of the middle ear cavity volume increased the hearing at 1.4-2.8kHz by 2.2dB (mean).
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