Microphone Array for Hearing Aids taking into Account the Scattering of the head

Jens Meyer

To appear at Workshop on Applications of Signal Processing to Audio and Acoustics (WASPAA01), Mohonk Mountain Resort, NY, 21-24 October 2001


This work describes the design of a robust microphone array with respect to the acoustic scattering from a head. In this sense, robust means that the major characteristics of the microphone array, like its directivity pattern or its directivity index (DI), vary only to a limited extent if the array is placed close to the head. Four different endfire arrays with a fixed filter and sum beamformer are simulated. For the simulations, the head is modeled as a sphere. The filters are designed to optimize the DI under a constraint for the white noise gain (WNG). Optimized filters for the free field as well as for the sphere mounted array will be used. It will be shown that a short array (4 cm) with three microphones will yield almost the same performance in free field as mounted close to a head. An intelligibility weighted DI (DIAI) of 7.0 dB is achieved with a minimum WNG of 6 dB. This result is verified by a measurement of the directivity pattern and the DI of the array in free field and eyeglass mounted on an artificial head.

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