Optimum microphone array for monaural and binaural in-the-canal hearing aids

Modern hearing aids include signal processing algorithms to improve the speech intelligibility by means of a microphone array, which can be monaural or binaural. In both cases, the signals are distorted by the well-known head-shadow effect that must be considered in the design. The main goal of this paper is to find the best microphone array configuration for in-the-canal hearing aids, constrained by the reduced dimension of such devices, in order to maximize the output gain and intelligibility when the array is steered to the desired direction. For this purpose, a total of 12 different array arrangements are compared, in terms of the array gain and intelligibility obtained by a Minimum Variance Distortionless Response (MVDR) beamformer, which also considers the head-shadow effect. The highest gain and intelligibility are obtained by a binaural array composed by a total of 8 microphones, 4 in diamond-shaped alignment in each ear. The results show the level of improvement achieved by increasing the number of microphones as well as using binaural arrays, giving rise to a compromise between the complexity of the array and the desired enhancement.