A Microphone Array for Hearing Aids
By: Bernard Widrow, PhD

Abstract:
A directional acoustic receiving system is constructed in the form of a
necklace including an array of two or more microphones mounted on a housing
supported on the chest of a user by a conducting loop encircling the users
neck. Signal processing electronics contained in the same housing receive and
combine the microphone signals in such a manner as to provide an amplified
output signal which emphasizes sounds of interest arriving in a direction
forward of the user. The amplified output signal drives the supporting
conducting loop to produce a representative magnetic field. An
electroacoustic transducer including a magnetic field pick up coil for
receiving the magnetic field is mounted in or on the users ear and generates
an acoustic signal representative of the sounds of interest. The microphone
output signals are weighted (scaled) and combined to achieve desired spatial
directivity responses. The weighting coefficients are determined by an
optimization process. By bandpass filtering the weighted microphone signals
with a set of filters covering the audio frequency range and summing the
filtered signals, a receiving microphone array with a small aperture size is
caused to have a directivity pattern that is essentially uniform over
frequency in two or three dimensions. This method enables the design of
highly-directive-hearing instruments which are comfortable, inconspicuous,
and convenient to use. The array provides the user with a dramatic
improvement in speech perception over existing hearing aid designs,
particularly in the presence of background noise, reverberation, and feedback. 

This paper will soon be published in the Circuits and Systems Magazine.
http://www-isl.stanford.edu/~widrow/paper.pdf
http://www-isl.stanford.edu/~widrow/paper.doc

Caption: Here is the picture of Dr Widrow wearing the Microphone Necklace

