Design of a high order binaural microphone array for hearing aids using a rigid spherical model

Wireless technology has allowed for a much wider variety in the design of microphone arrays for binaural hearing aids. To facilitate the design of these microphone arrays, this paper investigates the use of a spherical head model in the design of bilateral and binaural microphone arrays for hearing aids. The arrays have been designed using a free-field model, a spherical model, measurements on an artificial head, and measurements on an artificial head + torso. The results show that the free-field/spherical models over-estimate the speech-intelligibility weighted directivity index (SII-DI) of the bilateral and binaural arrays by respectively 0.9/0.4 and 0.8/0.5 dB. Furthermore the weights designed with the free-field/spherical model yield an SII-DI that is 0.7/0.6 dB lower for bilateral arrays and 0.9/0.9 dB lower for binaural arrays than the optimal SII-DI. Although the results show that the spherical model is better in predicting the DI than the free-field model, the spherical model does not design better weights.