Design of microphone arrays for hearing aids optimized to unknown subjects

The improvement of speech intelligibility in hearing aids is still an unsolved problem. Modern devices, either monaural or binaural, may include microphone arrays to provide directivity by means of spatial filtering, but the signals that arrive at the array are distorted by the so-called head shadow effect, which must be considered in the design. The fact that these effects are highly dependent on a person causes the design of an array customized for a subject to need a correct measurement of these effects, which is not practical in real scenarios. The lack of information about the head causes directivity reduction and distortions. In this work we propose three different methods to compute optimized filter coefficients with the purpose of maximizing the array gain and minimizing distortions, and with the objective that these filter coefficients are valid for all users. Furthermore, measurements of the amplitude and phase distortions caused by a lack of head information in the design are introduced. In addition, the methods proposed here have been evaluated in 13 different array configurations. Results show that these approaches reduce significantly the gain reduction and distortions, obtaining a similar intelligibility in comparison to the case where head information is available.