Development and assessment of two fixed-array microphones for use with hearing aids

Abstract

Hearing-impaired listeners often have great difficulty understanding speech in situations with background noise (e.g., meetings, parties) . Conventional hearing aids offer insufficient directivity to significantly reduce background noise relative to the desired speech signal . Based on array techniques, microphone prototypes have been developed with strongly directional characteristics to be incorporated into the frame and the "temples" of a pair of eyeglasses. Particular emphasis was on optimization and electronic stability . Computer simulations show that a directivity index of more than 10 dB can be obtained at the higher frequencies . Simulations were verified with free-field measurements . To investigate the influence of the human head on directivity, two portable models were also tested with a KEMAR manikin . The measurements show that the two models give an improvement of the signal-to-noise ratio of approximately 7 dB in a diffuse background noise field compared with an omnidirectional microphone . For the clinical assessment of these microphone arrays in the diffuse noise field (simulating a cocktail party situation), the speech-reception threshold in noise for simple Dutch sentences was determined with a normal single omnidirectional microphone and with one of the microphone arrays . The results of monaural listening tests of 30 subjects with normal hearing and 45 subjects with hearing impairment show that the microphone arrays give a mean improvement of the speech reception threshold in noise of about 7 dB compared with an omnidirectional microphone.