US 5,793,875 A · Directional hearing system

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 user's neck. Signal processing electronics contained in the same housing receives and combines 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 pickup coil for receiving the magnetic field is mounted in or on the user's 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 invention provides the user with a dramatic improvement in speech perception over existing hearing aid designs, particularly in the presence of background noise and reverberation.

Claims39

Dependent claims

A directional acoustic receiving system comprising a housing supported on the chest of a user, an array of three or more microphones arranged in a V-shaped pattern mounted on the housing and directed away from the user's chest, each providing an output signal representative of received sound, signal processing electronics mounted on said housing for receiving and combining the microphone signals in such a manner as to provide an output signal which emphasizes sounds of interest arriving in a direction forward of the user, and means for amplifying said output signal, said output signal coupled by wire to an earphone or earphones in the ear of the user, or coupled by wireless telemetry based on ultrasound, infrared, radio frequency radiation, or magnetic coupling.

A directional transmitting array wherein the transmitting elements are arranged in a plane and excited by the output of a signal processor, said signal processor multiplying the input signal with a variable gain used to control frequency response, band-pass filtering, and then multiplying by a vector of weights, each weighted band-passed signal added to the input of a different transmitting element, said signal processor multiplying said input signal again by another variable gain used to control frequency response, band-pass filtering in a different but contiguous frequency band, multiplying by another vector of weights, each weighted band-passed signal again added to the input of a different transmitting element, and so forth until the various contiguous frequency bands cover the full range of frequencies of interest, the values of each vector of weights chosen for the center of the associated band-filter by finding the best possible solution in some sense such as the least mean square sense or the least mean fourth sense to simultaneous equations of the form

D(.theta..sub.A,.theta..sub.E)-P(.theta..sub.A,.theta..sub.E,W)=0,
under the constraint that
1 1 . . . 1!W=1
where W is a column vector whose components are said vector of weights, where 1 1 . . . 1! is a row vector containing a number of components equal to the number of weights in W, where D(.theta..sub.A,.theta..sub.E) is the desired magnitude of the transmitting array's radiation pattern at said center frequency as a function of azimuth and elevation angles .theta..sub.A and .theta..sub.E, measured relative to a line perpendicular to the plane of the array, and where P(.theta..sub.A,.theta..sub.E,W) is the actual array radiation pattern at said center frequency as a function of .theta..sub.A, .theta..sub.E, and W, constraining the array to have a given radiation pattern magnitude in the look direction perpendicular to the plane of said array, to have radiation pattern magnitude of approximately zero in directions perpendicular to the look direction, and to have radiation pattern magnitudes at other specified angles of arrival that approximate desired radiation magnitudes, said simultaneous equations being solved either analytically or by automatic optimization means, providing a radiation pattern that has an almost uniform beam width over a range of frequencies whose corresponding wavelengths may vary from very short compared to the width and height of the array to 10 times the width or height of the array.

1 more element

A directional receiving array of receiving elements wherein the receiving elements are arranged in a plane, all receiving element output signals are weighted, summed, and band-pass filtered in a first frequency band, said receiving element output signals are weighted once again with a different set of weights, summed, and band-pass filtered in a different but contiguous frequency band, and so forth until the various contiguous frequency bands cover the full range of frequencies of interest, the values of each set of weights chosen for the center frequency of the associated band-pass filter by finding the best possible solution of simultaneous equations of the form

D(.theta..sub.A,.theta..sub.E)-P(.theta..sub.A,.theta..sub.E,W)=0
under the constraint that
1 1 . . . 1!W=1
where W is a column vector whose components are said set of weights, where 1 1 . . . 1! is a row vector containing a number of components equal to the number of weights in W, where D(.theta..sub.A,.theta..sub.E) is the desired sensitivity of the array's directivity pattern at said center frequency as a function of azimuth and elevation angles .theta..sub.A and .theta..sub.E, measured relative to a line perpendicular to the plane of the array, and where P(.theta..sub.A,.theta..sub.E,W) is the actual array sensitivity at said center frequency as a function of .theta..sub.A,.theta..sub.E, and W, the outputs of the band-pass filters weighted by variable gains to allow control of the frequency response of the receiving array, the weighted outputs of said band-pass filters summed to form the array output signal, constraining the array to have a given sensitivity in the look direction perpendicular to the plane of said array, to have a sensitivity of approximately zero in directions perpendicular to the look direction, and to have sensitivities at other specified angles of arrival that approximate desired sensitivities to provide a directivity pattern that has an almost uniform beam width over a practical range of frequencies whose corresponding wavelengths may vary from very short compared to the width and height of the array to 10 times the width or height of the array.

1 more element

A directional acoustic receiving array of microphones wherein the receiving microphones are arranged in a slightly warped plane, the microphone output signals are delayed to compensate for the signal delays introduced by the curvature of the array to acoustic waves arriving in the look direction, the delayed microphone signals are weighted, summed, and band-pass filtered, said delayed microphone output signals are weighted once again with a different set of weights, summed, and band-pass filtered in a different but contiguous frequency band, and so forth until the various contiguous frequency bands cover the full range of frequencies of interest, the values of each set of weights chosen for the center frequency of the associated band-pass filter by finding the best possible solution in some sense such as the least mean squares sense or the least mean fourth sense to simultaneous equations of the form

D(.theta..sub.A,.theta..sub.E)-P(.theta..sub.A,.theta..sub.E,W)=0
under the constraint that
(C.sup.T W).sup.2 +(S.sup.T W).sup.2 =1,
where W is a column vector whose components are said set of weights, where C is the corresponding column vector of the cosines of the phase delays to the individual microphones for a given sound source at said center frequency in the look direction, where S is the corresponding column vector of the sines of the phase delays to the individual microphones for said given sound source, where D(.theta..sub.A,.theta..sub.E) is the desired sensitivity of the array's directivity pattern at said center frequency as a function of azimuth and elevation angles .theta..sub.A and .theta..sub.E, measured relative to the look direction of the array, and where P(.theta..sub.0,.theta..sub.E,W) is the actual array sensitivity at said center frequency as a function of .theta..sub.A, .theta..sub.E, and W, the outputs of the band-pass filters weighted by variable gains to allow control of the frequency response of the receiving array, the weighted outputs of said band-pass filters summed to form the array output signal, constraining the array to have a given sensitivity in the look direction, to have a sensitivity of approximately zero in directions perpendicular to the look direction, and to have sensitivities at other specified angles of arrival that approximate desired sensitivities, said simultaneous equations being solved either analytically or by automatic optimization means, providing a directivity pattern that has an almost uniform beam width over a practical range of frequencies whose corresponding wavelengths may vary from very short compared to the width and height of the array to 10 times the width or height of the array.

1 more element

Dependencies are inferred from the claim text.

Directional hearing system

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Directional hearing system

Life of this patent

Abstract

Claims39