Directional hearing system

• US 5,793,875 A
• Filed: 04/22/1996
• Issued: 08/11/1998
• Est. Priority Date: 04/22/1996
• Status: Expired due to Fees

• Current Assignee: Cardinal Sound Labs, Inc.
• Original Assignee: Cardinal Sound Labs, Inc.
• Inventors: Lehr, Michael A., Widrow, Bernard
• Primary Examiner(s): Isen, Forester W.
• Application Number:
  US08/635,550
• Time in Patent Office: 841 Days
• Field of Search: 381/684, 381/92
• US Class Current: 381/313
• CPC Class Codes: H04R 2410/07 Mechanical or electrical reduction of wind noise generated by wind passing a microphone
• CPC Class Codes: H04R 25/405 by combining a plurality of transducers
• CPC Class Codes: H04R 25/407 Circuits for combining signals of a plurality of transducers
• CPC Class Codes: H04R 25/554 using a wireless connection, e.g. between microphone and amplifier or using Tcoils

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.

Claims

1. 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.

2. A directional acoustic receiving system comprising a housing curved to fit the torso and supported on the chest of a user by a conducting loop encircling the user'"'"'s neck, an array of three or more microphones mounted and positioned to conform to the curved housing and directed away from the user'"'"'s chest, said three or more microphones not an mounted along a single straight line, each of said microphones providing an output signal representative of received sound, signal processing electronics mounted on said housing for receiving ad 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, means for amplifying said output signal and applying it to the conductive neck loop to provide a magnetic field which is representative of said output signal, and electroacoustic transducer means including a magnetic field pick up coil for receiving said magnetic field and generating an acoustic signal representative of said sounds of interest.

3. The directional acoustic receiving system of claim 2 wherein said array comprises microphones directed substantially perpendicular to the direction of arrival of said sounds of interest, yielding a system that is directive both in azimuth and elevation.

4. The directional acoustic receiving system of claim 3 wherein said microphones of said array are arranged in a V-shaped pattern.

5. The directional acoustic receiving system of claim 2 wherein said microphones of said array are arranged in a square pattern or a circular pattern.

6. The directional acoustic receiving system of claim 2 wherein said signal processing electronics implement the array whose microphone signal weights are determined by an automatic optimization process to provide a given sensitivity in the look direction and a best fit to a desired directivity pattern in other directions, thereby combining said microphone signals to produce said array'"'"'s processed output signal.

7. The directional acoustic receiving system of claim 2 wherein the output signals of said microphones are delayed to compensate for the signal delays introduced by the curvature of said array to acoustic waves arriving from the direction of interest.

8. The directional acoustic receiving system of claim 3 wherein the output signals of said microphones are delayed to raise or to lower the elevation of the direction of interest of said array.

9. The directional acoustic receiving system of claim 2 wherein the output signals of said microphones are delayed to raise or to lower the elevation of the direction of interest of the array.

10. The directional acoustic receiving system of claim 2 wherein said microphones of said array are arranged in a V-shaped pattern or in a circular pattern, or in a square pattern.

11. The directional acoustic receiving system of claim 2 wherein said signal processing electronics uniformly weights and sums all of said microphone signals to provide said array'"'"'s processed output signal.

12. The directional acoustic receiving system of claim 2 wherein said signal processing electronics implement the array whose microphone signal weights are determined by a solution of simultaneous equations to provide a given sensitivity in the look direction and zero sensitivity in directions perpendicular to the look direction, thereby combining said microphone signals to produce said array'"'"'s processed output signal.

13. The directional acoustic receiving system of claim 2 wherein said signal processing electronics implement the array whose microphone signal weights are determined by an automatic optimization process to provide a given sensitivity in the look direction and a best fit to a desired directivity pattern in other directions, thereby combining said microphone signals to produce said array'"'"'s processed output signal.

14. The directional acoustic receiving system of claim 3 wherein said signal processing electronics uniformly weights and sums all of said microphone signals to provide said array'"'"'s processed output signal.

15. The directional acoustic receiving system of claim 3 wherein said signal processing electronics implements the array whose microphone signal weights are determined by a solution of simultaneous equations to provide a given sensitivity in the look direction and zero sensitivity in directions perpendicular to the look direction, thereby combining said microphone signals to produce said array'"'"'s processed output signal.

16. The directional receiving system of claim 3 wherein said signal processing electronics implements the array whose microphone signal weights are determined by an automatic optimization process to provide a given sensitivity in the look direction and a best fit to a desired directivity pattern in other directions, thereby combining said microphone signals to produce said array'"'"'s processed output signal.

17. The directional acoustic receiving system of claim 2 wherein said signal processing electronics implement the array whose microphone signal weights are determined by a solution of simultaneous equations to provide a given sensitivity in the look direction and zero sensitivity in directions perpendicular to the look direction, thereby combining said microphone signals to produce said array'"'"'s processed output signal.

18. 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

View Dependent Claims (38, 39)

38. The directional transmitting array of claim 18 wherein said array is designed and equipped to transmit audio-frequency acoustic waves, radio-frequency electromagnetic waves, radar waves, sonar waves, seismic waves, or ultrasonic acoustic waves.

39. The directional transceiver comprising the directional transmitting array of claim 18 combined with the directional receiving array of claim 19.

19. 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

View Dependent Claims (20, 21, 22, 23, 24, 25, 26, 27, 29, 34, 36)

20. The directional receiving array of the type of claim 19 wherein said receiving elements are microphones and the receiving array is a directional acoustic receiving array.

21. The directional receiving array of microphones of claim 20 wherein said microphones are directional microphones such as cardioid microphones, supercardioid microphones, or bidirectional gradient microphones, said microphones oriented so that direction of maximum microphone sensitivity coincides with the look direction of the array.

22. The directional acoustic receiving array of microphones of claim 20 wherein receiving microphones are placed in a V-shaped pattern having width approximately √

2 times the height, and having one or more receiving microphones located near the position that is centered vertically and horizontally.

23. The directional acoustic receiving array of microphones of claim 20 wherein receiving microphones are arranged along a horizontal line yielding a receiving array that is directive in azimuth and not in elevation.

24. The directional acoustic receiving array of microphones of claim 20 wherein receiving microphones are mounted on a support structure close to the chest or head of a user, or close to a wall, or table, or some other baffle-like structure that leaves the forward lobe of the directivity pattern unimpaired, but eliminates the back lobe by shadowing or by baffling.

25. The directional acoustic receiving array of microphones of claim 20 wherein said variable gains that control the frequency response have values that are stored in digital memory, the contents of the memory being changeable by internal means or by coupled external digital apparatus such as the serial port of a computer.

26. The directional acoustic receiving array of microphones of claim 20 wherein said variable gains that control the frequency response have values that are partially determined by power levels at the outputs of the corresponding band-pass filters, said power levels being measured by signal rectification or square law detection followed by moving average filtering, so that higher power sensed at the output of the individual band-pass filter causes a reduction of the corresponding gain value, with the final gain value determined by a combination of the power level and an external adjustment.

27. The directional acoustic receiving array of microphones of claim 20 wherein the output signals of said microphones are delayed to raise or to lower the elevation of the look direction of the array, its direction of maximum sensitivity.

29. The directional acoustic receiving array of microphones of claim 20 wherein said automatic optimization means is enhanced by adding random independent noise to the individual microphone sensitivity values causing P(θ

_A,θ

_E, W) to have a random component for each computation cycle, resulting in somewhat modified weight values that tend to have smaller magnitude differences, making the beam pattern less sharp but making said beam pattern less sensitive to natural variations in microphone sensitivity, and making the receiving array less sensitive to wind noise when used outdoors.

34. The directional acoustic receiving array of microphones of claim 20 wherein said receiving array is worn on a user'"'"'s chest and configured as a necklace comprising an array of two or more microphones mounted on a housing containing signal processing electronics designed to combine the microphone signals to emphasize sounds of interest arriving in the look direction forward of the user, supported by a conducting loop around the user'"'"'s neck that carries a current producing a magnetic field which is representative of said array'"'"'s processed output signal, said magnetic field providing inductive coupling to the telecoils of one or two hearing aids, thereby establishing a wireless connection between the directional signal of said array and the amplifiers of said hearing aids, said hearing aids delivering amplified directive sound to the ear or ears of the user.

36. The directional receiving array of claim 19 wherein said array is designed and equipped to receive radio-frequency electromagnetic waves, radar waves, sonar waves, seismic waves, or ultrasonic acoustic waves.

28. 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

View Dependent Claims (30, 31, 32, 33, 35, 37)

30. The directional acoustic receiving array of microphones of claim 28 wherein said automatic optimization means is enhanced by adding random independent noise to the individual microphone sensitivity values causing P(θ

_A,θ

_E, W) to have a random component for each computation cycle, resulting in somewhat modified weight values that tend to have smaller magnitude differences, making the beam pattern less sharp but making said beam pattern less sensitive to natural variations in microphone sensitivity, and making the receiving array less sensitive to wind noise when used outdoors.

31. The directional acoustic receiving array of microphones of claim 28 wherein the values of the weights that feed said band-pass filters and control the shape of the beam pattern are able to be altered by a user controlled switch so that the width of the beam pattern can be selected by the user.

32. The directional acoustic receiving array of microphones of claim 28 wherein the values of the gains that are fed by said band-pass filters and that control the shape of the frequency response of the array are able to be altered by a user controlled switch so that the frequency response can be selected by the user.

33. The directional acoustic receiving array of microphones of claim 28 wherein said receiving array is worn on a user'"'"'s chest and configured as a necklace comprising an array of three or more microphones mounted on a housing containing signal processing electronics designed to combine the microphone signals to emphasize sounds of interest arriving in the look direction forward of the user, a power source, and controls that may include on/off, volume, frequency response, and controls for other functions such as variabl e beam width, supported by a conducting loop around the user'"'"'s neck that carries a current producing a magnetic field which is representative of said arrays processed output signal, said magnetic field providing inductive coupling to the telecoils of one or two hearing aids, thereby establishing a wireless connection between the directional signal of said array and the amplifiers of said hearing aids, said hearing aids delivering amplified directive sound to the ear or ears of the user.

35. The directional acoustic receiving array of microphones of claim 28 wherein said receiving array is mounted on a housing worn on the chest or on the head with the array 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.

37. The directional acoustic receiving array of microphones of claim 28 wherein receiving microphones are placed in a substantially V-shaped pattern having width approximately √

2 times the height, and having one or more receiving microphones located near the position that is centered vertically and horizontally, with suitable choice of said desired sensitivity D(θ

_A,θ

_E), obtaining a beam width that is sharper in azimuth and elevation than would be obtained from array theory based on the formula of Lord Raleigh.