Method and apparatus for sound transduction with minimal interference from background noise and minimal local acoustic radiation

• US 7,477,751 B2
• Filed: 04/22/2004
• Issued: 01/13/2009
• Est. Priority Date: 04/23/2003
• Status: Expired due to Fees

• Current Assignee: Richard H. Lyon
• Original Assignee: RH Lyon Corp.
• Inventors: Bowen, David L., Lyon, Richard H., Unger, Gladys L.
• Primary Examiner(s): Chin; Vivian
• Assistant Examiner(s): Paul; Disler
• Application Number:
  US10/553,774
• Publication Number:
  US 20070086603A1
• Time in Patent Office: 1,727 Days
• Field of Search: 381/96, 381/92, 381/122, 381/59, 381/95, 381/71.1, 381/71.6, 381/26, 381/91, 381/93, 381/356, 379/406.05, 379/406.01, 379/406.06, 379/392.01, 379/388.07
• US Class Current: 381/96
• CPC Class Codes: H04R 2201/403 Linear arrays of transducers
• CPC Class Codes: H04R 23/00 Transducers other than those covered by groups H04R9/00 - H04R21/00 diaphragms for transducers of the distributed-mode type H04R7/045
• CPC Class Codes: H04R 3/005 for combining the signals of two or more microphones specially adapted for hearing aids H04R25/407

Abstract

A transducer senses sounds produced by a talker or other source and measures acceleration of air. Enhancement of acceleration is accompanied by reduction of the portion of the sound energy that escapes from the regions around the transducer. The result is a high sensitivity transducer, with increased privacy for use in communication systems, especially cell phones and in a multi-person environment. A pressure sensor array with a weighted output is sensitive to sound from a source talker only, and not to acoustic background noise, and not to a local loudspeaker. The weighted signal is a source sum pressure signal. The array produces a signal (using a different weighting) that corresponds to an estimate of a derivative of pressure. The derivative signal is proportional to the volume velocity fluctuations produced by the source. This signal is enhanced, rather than reduced. A local loudspeaker is driven to make the source sum pressure signal as small as desired. The loudspeaker is driven to produce volume velocity fluctuations approximately equal and opposite to those produced by the source. No compression of air arises due to the talker, and no sound is radiated into the far field. All happens because the system is driven to reduce the source pressure sum signal to below a desired threshold. It is not necessary to directly measure the volume velocity fluctuations of the talker source.

Claims

1. An apparatus for transducing an acoustic signal produced by a source, the signal having a frequency within a range from a low to a high, and corresponding wavelength within a range from a long to a short, the apparatus comprising:

a. an array of at least two pressure sensors spaced apart along a sensor axis and located at an array location;

b. a loudspeaker that is configured to output sound waves in response to an input, at a loudspeaker location that is on the sensor axis;

c. a first signal processor, coupled to an output from the array of pressure sensors, configured to generate a signal that corresponds to an estimate of a pressure derivative approximately along the sensor axis, at the array location;

d. a second signal processor, having an input that is coupled to an output of the first signal processor, and having an output that is coupled to the loudspeaker input, which second signal processor is configured to generate an output signal that is proportional to the estimate of derivative signal;

e. a third signal processor, coupled to an output from the array of pressure sensors, configured to generate a signal that corresponds to a weighted source pressure sum;

f. a comparator, coupled to an output of the third signal processor that generates the weighted pressure sum signal, configured to generate a pressure sum error signal that corresponds to whether the pressure sum signal is less than a threshold signal ε

; and

g. a fourth signal processor, coupled to an output of the comparator, configured to generate a coefficient signal based on the pressure sum error signal, which coefficient signal is input to the second signal processor which is further configured to generate an output signal that is proportional to the estimate of derivative signal, with a proportionality that is based on the coefficient signal.

2. The apparatus of claim 1, the fourth signal processor configured to generate a coefficient signal that results in the pressure sum being no greater than the threshold signals ε

.

3. The apparatus of claim 1, the fourth signal processor coupled to an output of the array further configured to generate the signal that corresponds to pressure sum as a sum of equally weighted outputs of sensors of the array.

4. The apparatus of claim 1, the fourth signal processor coupled to an output of the array further configured to generate the signal that corresponds to pressure sum as a sum of unequally weighted outputs of sensors of the array.

5. The apparatus of claim 4, further comprising a source input portion, the pressure sensor array and loudspeaker arranged such that the loudspeaker is more distant from the source input portion than is the array, the weighted pressure sum being chosen to establish a directional sensitivity to the pressure sensor array to discriminate in favor of sound coming from the direction of the source input portion.

6. The apparatus of claim 5, the weighted pressure sum being chosen to establish a cardioid directional sensitivity.

7. The apparatus of claim 5, the array comprising an array of three sensors, the weighted pressure sum being chosen to establish a superdirectivity substantially as shown in FIG. 12.

8. The apparatus of claim 5, the array comprising an array of at least two sensors, the weighted pressure sum being chosen to establish a superdirectivity.

9. The apparatus of claim 5, the weighted pressure sum comprising a frequency dependent weighting.

10. A telephone handset for transducing a talker'"'"'s speech, into a telephone transmission, the handset comprising:

a. a housing having a talker signal input portion;

b. an array of at least two pressure sensors, spaced apart along a sensor axis that passes through the talker signal input portion, arranged at an array location;

c. a loudspeaker at a loudspeaker location that is on the sensor axis and more distant from the talker signal input portion than it is from the array location;

d. a first signal processor, coupled to an output from the array of pressure sensors, configured to generate a signal that corresponds to an estimate of a pressure derivative approximately along the sensor axis, at the array location;

e. a second signal processor, having an input that is coupled to an output of the signal processor that generates an estimate of derivative signal, and having an output that is coupled to the loudspeaker input, which signal processor is configured to generate an output signal that is proportional to the estimate of derivative signal.

f. a third signal processor, coupled to an output from the array of pressure sensors, configured to generate a signal that corresponds to a weighted talker pressure sum;

g. a comparator, coupled to an output of the third signal processor that generates the weighted pressure sum signal, configured to generate a pressure sum error signal that corresponds to whether the pressure sum signal is less than a threshold signal ε

; and

h. a fourth signal processor, coupled to an output of the comparator, configured to generate a coefficient signal based on the pressure sum error signal, which coefficient signal is input to the second signal processor which is further configured to generate an output signal that is proportional to the estimate of derivative signal with a proportionality that is based on the coefficient signal.

11. The handset of claim 10, the fourth signal processor configured to generate a coefficient signal that results in the pressure sum being no greater than the threshold signal ε

.

12. The handset of claim 10, the fourth signal processor coupled to an output of the array further configured to generate the signal that corresponds to pressure sum as a sum of equally weighted outputs of sensors of the array.

13. The handset of claim 10, the fourth signal processor coupled to an output of the array further configured to generate the signal that corresponds to pressure sum as a sum of unequally weighted outputs of sensors of the array.

14. The handset of claim 13, further comprising a talker input portion, the pressure sensor array and loudspeaker arranged such that the loudspeaker is more distant from the talker input portion than is the array, the weighted pressure sum being chosen to establish a directional sensitivity to the pressure sensor array to discriminate in favor of sound coming from the direction of the talker input portion.

15. The handset of claim 14, the weighted pressure sum being chosen to establish a cardioid directional sensitivity.

16. The handset of claim 14, the array comprising an array of three sensors, the weighted pressure sum being chosen to establish a superdirectivity substantially as shown in FIG. 12.

17. The handset of claim 14, the array comprising an array of at least two sensors, the weighted pressure sum being chosen to establish a superdirectivity.

18. The handset of claim 14, the weighted pressure sum comprising a frequency dependent weighting.

19. An apparatus for transducing an acoustic signal produced in an acoustic medium by a source, the signal having a frequency within a range from a low to a high, and corresponding wavelength within a range from a long to a short, the apparatus comprising:

a. an acceleration sensor, located at a sensor location, arranged to sense acceleration of the medium, along a line and to generate a signal that corresponds to acceleration of the acoustic medium along the line;

b. a loudspeaker that is configured to output sound waves in response to an input, at a loudspeaker location that is spaced from the sensor location along the line;

c. an amplifying signal processor, having an input that is coupled to the acceleration sensor, which amplifying signal processor is coupled to an input of the loudspeaker, and configured to generate an output signal that is proportional to the acceleration signal;

d. an array of at least two pressure sensors spaced apart along a sensor axis and located at an array location that is spaced from the loudspeaker location along the line;

e. a sum signal processor, coupled to an output from the array of pressure sensors, configured to generate a signal that corresponds to a weighted source pressure sum;

f. a comparator, coupled to an output of the sum signal processor that generates the weighted pressure sum signal, configured to generate a pressure sum error signal that corresponds to whether the pressure sum signal is less than a threshold signal ε

; and

g. a coefficient signal processor, coupled to an output of the comparator, configured to generate a coefficient signal based on the pressure sum error signal, which coefficient signal is input to the amplifying signal processor, which is further configured to generate an output signal that is proportional to the estimate of derivative signal with a proportionality that is based on the coefficient signal.

20. The apparatus of claim 19, at least one of the pressure sensors comprising a microphone.

21. The apparatus of claim 19, at least one of the pressure sensors comprising a hydrophone.

22. An apparatus for transducing an acoustic signal produced by a source, the signal having a frequency within a range from a low to a high, and corresponding wavelength within a range from a long to a short, the apparatus comprising:

a. an array of at least two pressure sensors spaced apart along a sensor axis and located at an array location;

b. a loudspeaker that is configured to output sound waves in response to an input, at a loudspeaker location that is on the sensor axis;

c. a first signal processor, coupled to an output from the array of pressure sensors, configured to generate a signal that corresponds to an estimate of a pressure derivative approximately along the sensor axis, at the array location;

d. a second signal processor, having an input that is coupled to an output of the first signal processor that generates an estimate of pressure derivative signal, and having an output that is coupled to the loudspeaker input, which second signal processor is configured to generate an output signal that causes the loudspeaker to draw in any volume velocity fluctuations that are produced by the source;

e. a third signal processor, coupled to an output from the array of pressure sensors, configured to generate a signal that corresponds to a weighted source pressure sum;

f. a comparator, coupled to an output of the third signal processor that generates the weighted pressure sum signal, configured to generate a pressure sum error signal that corresponds to whether the pressure sum signal is less than a threshold signal ε

; and

g. a fourth signal processor, coupled to an output of the comparator, configured to generate a coefficient signal based on the pressure sum error signal, which coefficient signal is input to the second signal processor which is further configured to generate an output signal that is proportional to the estimate of derivative signal with a proportionality that is based on the coefficient signal.

23. The apparatus of claim 22, the fourth signal processor configured to generate a coefficient signal that results in the pressure sum being no greater than the threshold signal ε

.

24. The apparatus of claim 22, the fourth signal processor coupled to an output of the array further configured to generate the signal that corresponds to pressure sum as a sum of unequally weighted outputs of sensors of the array.

25. An apparatus for transducing sound produced by a talker at a talker location, the apparatus comprising:

a. an array of at least two pressure sensors spaced apart along a sensor axis and located at an array location;

b. a loudspeaker, at a loudspeaker location that is on the sensor axis;

c. a signal processor, coupled to an output from the array of pressure sensors, configured to generate a signal that corresponds to an estimate of pressure derivative, approximately along the sensor axis, at the array location;

d. a signal processor, coupled to an output from the array of pressure sensors, configured to generate a signal that corresponds to a weighted sum of an acoustic parameter at the array location, the weighting chosen to establish a directional sensitivity to the pressure sensor array to discriminate in favor of sound coming from the direction of the talker location;

e. a comparator, coupled to an output of the signal processor that generates a weighted sum signal, configured to generate an error signal that corresponds to a difference between the weighted sum of the acoustic parameter and a threshold ε

;

f. a signal processor, coupled to an output of the comparator, configured to generate a coefficient signal based on the error signal, which coefficient signal is input to a signal generator that has an input that is coupled to an output of the signal processor that generates an estimate of derivative signal and an output that is coupled to the loudspeaker input, the signal generator being further configured to generate an output signal that;

i. is proportional to the derivative signal with a degree of proportionality that is based on the coefficient signal; and

ii. results in the weighted sum of the acoustic parameter being no greater than the threshold ε

.

26. An apparatus for transducing an acoustic signal produced by a source, the signal having a frequency within a range from a low to a high, and corresponding wavelength within a range from a long to a short, the apparatus comprising:

a. a pressure sensor located at a sensor location, on a sensor line from a source input portion, which sensor is configured to generate a signal that is proportional to sound pressure;

b. a loudspeaker that is configured to output sound waves in response to an input, at a loudspeaker location that is on the sensor line;

c. a first signal processor, having an input that is coupled to the pressure sensor and having an output signal that is proportional to the pressure signal, which output signal is coupled to;

i. the loudspeaker input; and

ii. a comparator, configured to generate a pressure error signal that corresponds to whether the pressure signal is less than a threshold signal ε

; and

d. a second signal processor, coupled to an output of the comparator, configured to generate a coefficient signal based on the pressure error signal, which coefficient signal is input to the first signal processor, which is further configured to generate an output signal that is proportional to the pressure signal with a proportionality that is based on the coefficient signal.

27. A method for transducing an acoustic signal produced in an acoustic medium by a source at a source location, the signal having a frequency within a range from a low to a high, and corresponding wavelength within a range from long to short, the method comprising the steps of:

a. measuring acceleration of the acoustic medium, along a line that passes through the source location, at a sensor location, spaced from the source location;

b. generating a signal that is proportional to the measured acceleration;

c. driving a loudspeaker, located on the sensor axis, spaced away from the source location farther than the array location, with a signal that is proportional to the acceleration signal;

d. using an array of at least two pressure sensors spaced apart along a sensor axis that is collinear with the line, and located at an array location that is spaced from the loudspeaker location along the line;

e. generating a signal that corresponds to a weighted source pressure sum of outputs from the at least two sensors;

f. comparing the weighted source pressure sum to a threshold signal ε and

, based on the comparison, generating a pressure sum error signal that corresponds to whether the pressure sum signal is less than the threshold;

g. generating a coefficient signal based on the pressure sum error signal; and

h. generating an output signal that is proportional to the estimate of derivative signal, with a proportionality that is based on the coefficient signal.