Variable gain active noise canceling system with improved residual noise sensing

• US 6,118,878 A
• Filed: 11/05/1997
• Issued: 09/12/2000
• Est. Priority Date: 06/23/1993
• Status: Expired due to Term

• Current Assignee: Noise Cancellation Technologies, Inc. (NCT Group, Inc.)
• Original Assignee: Noise Cancellation Technologies, Inc. (NCT Group, Inc.)
• Inventors: Jones, Owen
• Primary Examiner(s): Isen, Forester W.
• Assistant Examiner(s): Mei, Xu
• Application Number:
  US08/968,873
• Time in Patent Office: 1,042 Days
• Field of Search: 381/71.2, 381/94, 381/73.1, 381/25, 381/74, 381/322, 381/328, 381/317, 381/367, 381/354, 381/353
• US Class Current: 381/72
• CPC Class Codes: A61F 11/145 electric, e.g. for active noise reduction
• CPC Class Codes: G10K 11/17823 Reference signals, e.g. ambient acoustic environment
• CPC Class Codes: G10K 11/17835 using detection of abnormal input signals
• CPC Class Codes: G10K 11/17853 of the filter
• CPC Class Codes: G10K 11/17855 for improving speed or power requirements
• CPC Class Codes: G10K 11/17857 Geometric disposition, e.g. placement of microphones
• CPC Class Codes: G10K 11/17881 the reference signal being an acoustic signal, e.g. recorded with a microphone
• CPC Class Codes: G10K 11/17885 additionally using a desired external signal, e.g. pass-through audio such as music or speech
• CPC Class Codes: G10K 2210/108 Communication systems, e.g. where useful sound is kept and noise is cancelled
• CPC Class Codes: G10K 2210/1081 Earphones, e.g. for telephones, ear protectors or headsets
• CPC Class Codes: G10K 2210/3011 Single acoustic input
• CPC Class Codes: G10K 2210/3013 Analogue, i.e. using analogue computers or circuits
• CPC Class Codes: G10K 2210/3019 Cross-terms between multiple in's and out's
• CPC Class Codes: G10K 2210/3028 Filtering, e.g. Kalman filters or special analogue or digital filters
• CPC Class Codes: G10K 2210/3056 Variable gain
• CPC Class Codes: G10K 2210/3214 Architectures, e.g. special constructional features or arrangements of features
• CPC Class Codes: G10K 2210/503 Diagnostics; Stability; Alarms; Failsafe

Abstract

An active noise cancellation system includes a series of features for more effective cancellation, greater reliability, and improved stability. A particular feature adapted for headset systems includes locating a residual microphone radially offset from the center of a sound generator to detect a signal more similar to that incident upon the eardrum of the user. In addition, an open back headset design includes perforations on the side of the headset instead of the back, so that the perforations are less susceptible to inadvertent blockage. The system also includes a mechanism for detecting changes in the acoustic characteristics of the environment that may be caused, for example, by pressure exerted upon the earpieces, and that may destabilize the cancellation system. The system automatically responds to such changes, for example, by reducing the gain or the frequency response of the system to preserve stability. The system further includes other methods for detecting imminent instability and compensating, such as detecting the onset of signals within enhancement frequencies characteristic of the onset of instability, and adjusting the gain or frequency response of the system or suppressing the enhanced signals. The system further includes a mechanism for conserving battery life by turning the system off when sound levels are low, or adjusting the power supply to the system to correspond to the current power requirements of the system.

Claims

1. An active noise canceling headset system comprising an earpiece adapted to be held against a user'"'"'s ear, the earpiece comprising:

a sound generator disposed with said earpiece, for generating an anti-noise field in response to drive signals applied thereto;

a first sensor disposed within the anti-noise field, for generating a residual signal indicative of the sum of ambient sounds and anti-noise impinging on the sensor;

a processor for generating the drive signals to the sound generator in accordance with said residual signal;

means for approximating the ambient sound perceived at the user'"'"'s ear;

means for enhancing the low frequency response of the earpiece;

means for providing a selected desired signal to the user'"'"'s ear through the sound generator cancellation;

means for selectively varying the transfer function of the system in response to predetermined conditions indicative of potential instability; and

means for generating indicia of conditions indicative of reduced power needs of the system and responsively decreasing power consumption of predetermined portions of the system.

2. The system of claim 1, wherein the first sensor is disposed within said anti-noise field radially offset from the noisefield center such that the residual signal generally approximates the sound at the users eardrum.

3. An earpiece adapted to be held proximate a user'"'"'s ear, the earpiece comprising:

a sound generator, responsive to drive signals applied thereto, for generating anti-noise;

a sensor for generating a residual signal indicative of the sum of ambient sounds and anti-noise at the location of the sensor;

the sensor being disposed off center from said sound generator in an optimal position calculated in accordance with a plurality of acoustic parameters at the user'"'"'s eardrum such that the amplitude of the anti-noise at the residual microphone is diminished and the residual signal generally approximates the sound at the user'"'"'s eardrum, wherein the plurality of acoustic parameters include, but are not limited to, the distance of the sound generator from the user'"'"'s eardrum and the size of an inner cavity at the user'"'"'s ear.

4. The earpiece of claim 3, wherein the sensor is disposed off center from said sound generator in a direction corresponding to the top of the user'"'"'s head.

5. The earpiece of claim 3, further comprising:

a processor that generates the drive signals to the sound generator in accordance with said residual signal.

6. The earpiece of claim 5, wherein the processor includes mean for varying its transfer function in response to the sum of ambient sounds at the location of the sensor.

7. The earpiece of claim 3, wherein the sensor being at least partially acoustically shielded from said sound generator by a protective barrier that prevents the residual signal from being directly received by the sensor such that the residual signal generally approximates the sound at the user'"'"'s eardrum.

8. An earpiece adapted to be held proximate a user'"'"'s ear, the earpiece comprising:

a sound generator, responsive to drive signals applied thereto, for generating anti-noise;

a sensor for generating a residual signal indicative of the sum of ambient sounds and anti-noise at the location of the sensor; and

an exterior shell comprising an forward lip for disposition proximate the users ear, a rear portion, and a transverse portion intermediate said lip and rear portions forming an interior cavity; and

at least one aperture in a transverse portion, inset from said forward lip, of said exterior shell communicating with said interior cavity disposed rearwardly of said sound generator to enhance low frequency response of the earpiece and,

wherein the transverse portion is a side wall joining the forward lip to the rear portion that is substantially perpendicular to the rear wall in the region of the at least one aperture and wherein the location of said at least one aperture in the traverse wall provides protection from blockage of said at least one aperture.

9. The earpiece of claim 8, further comprising:

a processor that generates the drive signals to the sound generator in accordance with said residual signal.

10. The earpiece of claim 9, wherein the processor includes mean for varying its transfer function in response to the sum of ambient sounds at the location of the sensor.

11. An active noise cancelling system, comprising:

a sound generator for generating an anti-noise field in response to drive signals applied thereto;

a first sensor, disposed with the anti-noise field, for generating a residual signal indicative of the sum of ambient sounds and anti-noise impinging on the sensor;

a processor for generating the drive signals to the sound generator in accordance with said residual signal;

the first sensor cooperating with processor and the sound generator to form a feed back loop producing a feedback signal, wherein the processor generates the drive signals according to a transfer function characteristic of acoustic properties of the feedback loop; and

filter means contained within the processor that filters the feedback signal for selectively varying the transfer function of the system in response to predetermined changes in acoustic conditions indicative of potential instability, wherein the filter means has a transfer characteristic that is not changed by the feedback signal; and

wherein the feedback signal is processed by said processor to form a component of said anti-noise field.

12. The active noise cancelling system of claim 11, further comprising:

an active headset having the sound generator and the first sensor as a sound generation and sound sensing means; and

a control unit having the processor,

wherein the active headset is removably coupled to the control unit.

13. The noise cancellation system of claim 12, wherein the headset is removably coupled to the control unit through a connector.

14. The active noise canceling system of claim 11, wherein the means for selectively varying the transfer function of the system in response to predetermined conditions indicative of potential instability comprises:

a gain control circuit comprising at least one element capable of changing the gain of the feedback loop.

15. The active noise cancelling system of claim 11, wherein the means for selectively varying the transfer function of the system in response to predetermined conditions indicative of potential instability comprises at least a pressure transducer element capable of varying the frequency response of the feedback loop.

27. The system of claim 13, wherein:

the processor includes means for varying its transfer function in response to the signal indicative of ambient noise.

16. A method for cancelling noise perceived by a user comprising the steps of:

generating, in accordance with drive signals, an anti-noise field;

sensing residual noise resulting from interaction of the anti-noise and ambient noise within the anti-noise field;

generating the drive signals in accordance with said sensed residual noise pursuant to an associated transfer function;

sensing noise outside the anti-noise field;

generating indicia of predetermined changes in acoustic conditions indicative of potential instability by comparing a ratio of an internal noise amplitude of the residual noise to an external noise amplitude outside the anti-noise field within a predetermined frequency range to a reference level; and

selectively varying the transfer function in accordance with said indicia.

17. A method for cancelling noise perceived by a user comprising the steps of:

generating, in accordance with drive signals, an anti-noise field;

sensing the residual noise resulting from interaction of the anti-noise and ambient noise within the anti-noise field;

generating the drive signals in accordance with said sensed residual noise pursuant to an associated transfer function;

generating indicia of predetermined conditions indicative of potential instability by sensing variations in a ratio between sounds within a predetermined frequency range outside of said anti-noise field to sounds within said predetermined frequency range within said anti-noise field; and

selectively varying the transfer function in accordance with said indicia.

18. A method for cancelling noise perceived by a user comprising the steps of:

generating, in accordance with drive signals, an anti-noise field;

sensing the residual noise resulting form interaction of the anti-noise and ambient noise within the anti-noise field;

generating the drive signals in accordance with said sensed residual noise pursuant to an associated transfer function, wherein said generating anti-noise and sensing residual noise steps are effected within an earpiece;

generating indicia of predetermined conditions indicative of potential instability by sensing the pressure against the earpiece; and

selectively varying the transfer function in accordance with said indicia.

19. The method of claim 18, wherein sensing the pressure against the earpiece is performed by at least one switchable element capable of changing state when the pressure of an earpiece against a user'"'"'s head is sensed to be outside a predetermined range of acceptable pressure.

20. The method of claim 18, wherein the pressure against the earpiece is sensed by measuring, at a microphone output, the amplitude of a subsonic signal applied to an earphone containing the earpiece.

21. The method of claim 20, the earpiece comprising:

a sound generator mounted within the earpiece, responsive to drive signals applied thereto, for generating an anti-noise;

a microphone mounted within the earpiece;

a cancellation circuit, wherein a feedback loop is formed between said sound generator and said microphone through said cancellation circuit, that produces a cancellation signal;

a subsonic frequency signal generator that generates a subsonic frequency signal that is inaudible to a user of the earpiece; and

a summing circuit, coupled to said cancellation circuit and said subsonic frequency signal generator, that sums the cancellation signal and the subsonic frequency signal to produce a signal that is presented to said sound generator.

22. The earpiece of claim 21, wherein the earpiece further comprises:

a filter that receives a signal from said microphone and that transmits subsonic frequency signals; and

a rectifying circuit that receives the subsonic frequency signals transmitted by said filter and that rectifies and smoothes the subsonic frequency signals to generate DC levels that are representative of the amplitude of the subsonic frequency signals; and

an amplifier, having a gain, that receives the DC level generated by the rectifying circuit, wherein the gain is adjusted according to the pressure of the earpiece against the user'"'"'s head as reflected in the DC levels.

23. The earpiece of claim 22, wherein said filter is a low pass filter.

24. The earpiece of claim 22, wherein said filter is a bandpass filter.

25. An active noise cancelling headset system, comprising:

a sound generator, disposed with an earpiece, for generating an anti-noise field in response to drive signals applied thereto;

a first sound sensor, disposed within an anti-noise field, for generating a residual signal indicative of the sum of ambient noise and anti-noise impinging on the sensor;

a second sound sensor disposed a predetermined distance from said sound generator and output of said anti-noise field to generate a signal indicative of ambient noise; and

a processor, for generating the drive signals to the sound generator in accordance with said residual signal and said signal indicative of said ambient noise;

filter means contained within the processor that has a transfer characteristics; and

wherein said first sound sensor is connected to cooperate with said processor and said sound generator to form a feedback loop producing a feedback signal, and said second sound sensor is connected to cooperate with said processor and said sound generator to provide feedforward signal noise cancellation, said feedforward and feedback signals being processed by said processor to form a component of said anti-noise field, and

wherein the feedback signal does not change the transfer characteristic of the filter means.

26. The system of claim 25, wherein:

the first sound sensor is connected to cooperate with the processor and the sound generator to form a feed back loop; and

the system further includes means, cooperating with the second sound sensor, for attenuating high frequency components of the ambient noise at the eardrum.

28. An active noise cancelling system, comprising:

a sound generator, responsive to drive signals applied thereto, for generating an anti-noise field;

a first sound sensor disposed with the anti-noise field to generate a residual signal indicative of the sum of ambient sounds and anti-noise impinging on the sensor;

a second sound sensor disposed a predetermined distance from said sound source and outside of said noise field to generate a signal indicative of ambient noise;

a noise cancellation processor having a transfer characteristics, for generating the drive signals to the sound generator;

the first sensor being connected to cooperate with the processor and the sound generator to form a feed back loop producing a feedback signal; and

the second sensor being connected to cooperate with the processor and the sound generator to provide feedforward signal noise cancellation;

wherein the noise cancellation processor processes the feedforward signal and the feedback signal to form a component of said anti-noise field and wherein the feedback signal does not modify the transfer characteristics of the noise cancellation processor.

29. The system of claim 28, including means for attenuating high frequency components of the ambient noise at the eardrum.

30. An active noise cancelling system comprising:

a sound generator, responsive to drive signals applied thereto, for generating an anti-noise field;

a first sound sensor disposed within said anti-noise field to generate a residual signal indicative of the sum of ambient sounds and anti-noise impinging on the sensor;

a noise cancellation processor, for generating the drive signals to the sound generator; and

means for generating indicia of conditions indicative of reduced power needs of the system and responsively varying the transfer function of the system in response said indicia.

31. The system of claim 30, wherein the means for generating indicia of predetermined conditions indicative of reduced power needs comprises means for sensing the level of ambient noise.

32. The system of claim 30, further comprising an earpiece and wherein:

the sound source and the first sound sensor are disposed within the earpiece; and

the means for generating indicia of predetermined conditions indicative of reduced power needs comprises means for sensing the pressure against the earpiece.

33. A method for conserving power in an active noise cancelling system, the method comprising the steps of:

generating, in accordance with drive signals, an anti-noise field;

sensing the residual noise resulting from interaction of the anti-noise and ambient noise within the anti-noise field;

generating the drive signals in accordance with said sensed residual noise;

generating indicia of the amplitude of ambient noise; and

selectively varying the level of power applied to portions of a processor of the system in accordance with said indicia of amplitude of ambient noise.

34. The method of claim 33, further comprising:

varying the transfer function of a processor, that generates the drive signals, in response to said indicia of the amplitude of ambient noise.

35. A method for cancelling noise perceived by a user comprising the steps of:

generating, in accordance with drive signals, an anti-noise field centered at a location proximate to the users ear;

sensing the residual noise resulting from superposition of the anti-noise and ambient noise at an optimal location radially offset from the center of the anti-noise field in accordance with a plurality of acoustic parameters at the user'"'"'s eardrum to simulate noise cancellation conditions at the user'"'"'s eardrum, wherein at the optimal location the amplitude of the anti-noise is diminished and wherein the plurality of acoustic parameters include, but are not limited to, the distance of a sound generator from the user'"'"'s eardrum and the size of an inner cavity at the user'"'"'s ear; and

generating the drive signals in accordance with said sensed residual noise.

36. The method of claim 35, comprising the further step of:

varying a transfer function of a processor, that generates the drive signals, in response to the ambient noise portion of the residual noise.

37. The method of claim 35, further comprising:

varying the transfer function of a processor, that generates the drive signals, in response to the ambient noise.

38. The method of claim 35, wherein the step of sensing the residual noise comprises:

placing a protective barrier with respect to the sensor to operatively prevent the anti-noise field from being directly received by the sensor such that the residual noise generally approximates the sound at the user'"'"'s eardrum.

39. A method for increasing the stability of an active noise cancelling system comprising a noise cancellation circuit, a sound sensor and sound generator cooperating in a feedback loop, the feedback loop having an associated transfer function, the transfer function with respect to components of ambient noise within a predetermined range of frequencies tending to vary with approaching instability of the system, the method including the steps of:

generating, in accordance with drive signals, an anti-noise field;

sensing the residual noise resulting from interaction of the anti-noise and ambient noise;

generating the drive signals in accordance with said sensed residual noise;

sensing variations in the transfer function of the system with respect to components of ambient noise within said predetermined range of frequencies; and

varying the transfer function of the system in accordance with said sensed variations, wherein varying the transfer function of the system does not vary a transfer function of a filter means that varies the transfer function of the system.

40. The method of claim 39, further comprising:

varying the transfer function in response to components of ambient noise within the predetermined range of frequencies.

41. A method for increasing the stability of an active noise cancelling system comprising a noise cancellation circuit, a sound sensor and sound generator cooperating in a feedback loop, the feedback loop having an associated transfer function, the transfer function with respect to components of ambient noise within a predetermined range of frequencies tending to vary with approaching instability of the system, the method including the steps of:

generating, in accordance with drive signals, an anti-noise field;

sensing the residual noise resulting from interaction of the anti-noise and ambient noise;

generating the drive signals in accordance with said sensed residual noise;

sensing variations in the transfer function of the system with respect to components of ambient noise within said predetermined range of frequencies by determining the ratio of the amplitude of components of ambient noise within said predetermined range of frequencies at a location outside of said noise field and components within said predetermined range of frequencies at a location within said noise field; and

varying the transfer function of the system in accordance with said sensed variations by reducing the gain of the system in response to the ratio of the signals exceeding a predetermined threshold value.

42. An active noise cancelling system, comprising:

a sound generator for generating an anti-noise field in response to drive signals applied thereto;

a first sensor, disposed with the anti-noise field, for generating a residual signal indicative of the sum of ambient sounds and anti-noise impinging on the sensor;

a processor for generating the drive signals to the sound generator in accordance with said residual signal;

the first sensor cooperating with processor and the sound generator to form a feed back loop producing a feedback signal, wherein the processor generates the drive signals according to a transfer function characteristic of acoustic properties of the feedback loop; and

filter means contained within the processor that filter the feedback signal for selectively varying the transfer function of the system in response to predetermined changes in acoustic conditions indicative of potential instability, wherein the filter means for selectively varying the transfer function of the system in response to predetermined conditions indicative of potential instability comprises;

at least one switchable element capable of changing state when the pressure of an earpiece against a user'"'"'s head is sensed to be outside a predetermined range of acceptable pressure; and

wherein the feedback signal is processed by said processor to form a component of said anti-noise field.

43. The active noise canceling system of claim 42, wherein said at least one switchable element is capable of selectively deactivating a controller of said processor to control power supplied to said processor.

44. The active noise canceling system of claim 42, wherein said at least one switchable element is a momentary contact membrane switch.

45. The active noise canceling system of claim 42, wherein the means for selectively varying the transfer function of the system in response to predetermined conditions indicative of potential instability further comprises:

hysteresis circuitry that cooperatively operates with said at least one switchable element to prevent said at least one switchable element from fluctuating near a threshold pressure of said predetermined range of acceptable pressure.

46. The active noise canceling system of claim 45, wherein said hysteresis circuitry is incorporated in said at least one switchable element.

47. An active noise cancelling system, comprising:

a sound generator for generating an anti-noise field in response to drive signals applied thereto;

a first sensor, disposed with the anti-noise field, for generating a residual signal indicative of the sum of ambient sounds and anti-noise impinging on the sensor;

a processor for generating the drive signals to the sound generator in accordance with said residual signal;

the first sensor cooperating with processor and the sound generator to form a feed back loop producing a feedback signal, wherein the processor generates the drive signals according to a transfer function characteristic of acoustic properties of the feedback loop; and

filter means contained within the processor that filter the feedback signal for selectively varying the transfer function of the system in response to predetermined changes in acoustic conditions indicative of potential instability, wherein the filter means comprises;

a gain control circuit comprising at least one element capable of changing the gain of the feedback loop, wherein said control circuit comprises at least one switchable element to change the gain of the feedback loop; and

wherein the feedback signal is processed by said processor to form a component of said anti-noise field.

48. An active noise cancelling system, comprising:

a sound generator for generating an anti-noise field in response to drive signals applied thereto;

a first sensor, disposed with the anti-noise field, for generating a residual signal indicative of the sum of ambient sounds and anti-noise impinging on the sensor;

a processor for generating the drive signals to the sound generator in accordance with said residual signal;

the first sensor cooperating with processor and the sound generator to form a feed back loop producing a feedback signal, wherein the processor generates the drive signals according to a transfer function characteristic of acoustic properties of the feedback loop; and

filter means contained within the processor that filter the feedback signal for selectively varying the transfer function of the system in response to predetermined changes in acoustic conditions indicative of potential instability, wherein the filter means comprises;

a gain control circuit comprising at least one element capable of changing the gain of the feedback loop, wherein said control circuit comprises at least one pressure transducer element to change the gain of the feedback loop; and

wherein the feedback signal is processed by said processor to form a component of said anti-noise field.

49. An active noise cancelling system, comprising:

a sound generator for generating an anti-noise field in response to drive signals applied thereto;

a first sensor, disposed with the anti-noise field, for generating a residual signal indicative of the sum of ambient sounds and anti-noise impinging on the sensor;

a processor for generating the drive signals to the sound generator in accordance with said residual signal;

the first sensor cooperating with processor and the sound generator to form a feed back loop producing a feedback signal, wherein the processor generates the drive signals according to a transfer function characteristic of acoustic properties of the feedback loop;

filter means contained within the processor that filter the feedback signal for selectively varying the transfer function of the system in response to predetermined changes in acoustic conditions indicative of potential instability;

means for selectively deactivating one or more portions of a controller of said processor to control power supplied to said processor, and

wherein the feedback signal is processed by said processor to form a component of said anti-noise field.

50. The active noise canceling system of claim 49, wherein the means for selectively deactivating the controller of said processor comprises at least one switchable element.

51. The active noise canceling system of claim 49, further comprising a pressure transducer element, wherein the pressure transducer element is capable of sensing changes in the pressure of the headset against the user'"'"'s ear and allows the means for selectively deactivating one or more portions of the controller to deactivate one or more portions of the controller when the pressure sensed by the pressure transducer element is outside a predetermined pressure range.