A Microphone Array for Hearing Aids

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. Microphone Array for Hearing Aids There is a big difference between hearing speech and understating speech. Most hearing-impaired people will be able to hear speech when given sufficient amplification from their hearing aids. In many cases, however, they will hear but will not understand. There are limitations to the benefits of amplification alone. In a noisy place, hearing aids will amplify the noise as well as the desired speech signal. In a reverberant place, hearing aids will amplify late multipath arrivals as well as the direct first-arrival signal. Furthermore, feedback associated with high output hearing aids distorts the frequency response of the hearing aid (which was carefully tuned to compensate for the individual’s hearing loss) and sometimes causes oscillation. A microphone array for hearing aids is described that overcomes some of these limitations and has the capability of enhancing speech understanding for hearing-impaired patients. The microphone array is worn on the chest as part of a necklace, in accord with the diagram of Fig. 1. A processed signal from the array drives current through a conducting neck loop thus creating a time-variable magnetic field that is representative of the received sound. The magnetic field provides a wireless means for carrying the sound signal to conventional hearing aid devices located in the ears of the wearer. In order to receive the signal, the hearing aid must be equipped with a “telecoil”, a small induction coil contained within the hearing aid whose output can be switch selected by the wearer to serve in place of the hearing aid’s microphone signal. When switching the hearing aid to telecoil position, the wearer hears the sound received by the array. When switching the hearing aid to the microphone position, the wearer hears the usual sound received by the hearing aid’s own microphone. The original purpose of the telecoil was to enable the hearing aid wearer to converse over the telephone. A hearing-aid compatible telephone receiver radiates a time varying magnetic field corresponding to the telephone signal. This is generally leakage flux from the receiver. Using the telecoil, many patients can hear over the telephone much more effectively. We are able to take advantage of the telecoil, which is commonly available in the most powerful behind-the-