DIRECTIONAL HEARING-AID BASED ON ARRAY TECHNOLOGY

The hearing impaired often have great difficulty understanding speech in surroundings with background noise or reverberation. A directional hearing aid might be beneficial in reducing background noise in relati on to the desired speech signal. To this end microphone systems were d eveloped with strongly directional characteristics, using array techni ques. Considerable attention was paid to optimization and stability. F ree-field simulations of several robust models showed that a directivi ty index of 9 dB can be obtained. Simulations were verified with a lab oratory model. Based on simulations and measurements, two portable pro totypes were developed and tested using a KEMAR-manikin. The KEMAR-mea surements showed that the two prototypes gave an improvement of the si gnal to noise ratio of 7 dB in a fully diffuse sound field. The benefi t of these microphone arrays for the hearing impaired was tested in a sound insulated room. One loudspeaker was placed in front of the liste ner simulating the partner in a discussion, and a diffuse background n oise was produced by eight loudspeakers placed on the corners of a cub e. The hearing impaired subject was seated in the centre of the cube. The speech-reception threshold in noise for simple Dutch sentences was determined with a normal single omni-directional microphone and with one of the prototypes. The results of the listening tests with 45 hear ing impaired subjects showed an average improvement of the S/N-ratio o f 7.0 dB for monaural fitting.