Active noise reducing

• US 5,293,425 A
• Filed: 12/03/1991
• Issued: 03/08/1994
• Est. Priority Date: 12/03/1991
• Status: Expired due to Fees

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Zangi, Kambiz C., Feder, Meir, Weinstein, Ehud, Oppenheim, Alan V.
• Primary Examiner(s): Isen, Forester W.
• Application Number:
  US07/802,121
• Time in Patent Office: 826 Days
• Field of Search: 381/71, 381/94
• US Class Current: 381/71.8
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17875 using an error signal without a reference signal, e.g. pure feedback
• CPC Class Codes: G10K 2210/1281 Aircraft, e.g. spacecraft, airplane or helicopter
• CPC Class Codes: G10K 2210/3011 Single acoustic input
• CPC Class Codes: G10K 2210/30232 Transfer functions, e.g. impulse response
• CPC Class Codes: G10K 2210/3028 Filtering, e.g. Kalman filters or special analogue or digital filters
• CPC Class Codes: G10K 2210/3055 Transfer function of the acoustic system
• CPC Class Codes: H03H 21/0012 Digital adaptive filters

Abstract

A noise reducing system includes an input transducer that energizes an adaptive filter. The adaptive filter energizes an output transducer that creates a noise reducing field at the input transducer.

Claims

1. Active noise reducing apparatus comprising,

an input transducer that provides a transduced input signal,

an adaptive filter having an input coupled to said input transducer,

an output transducer coupled to the output of said adaptive filter that transducer the signal on said adaptive filter output to provide a transduced signal to create a noise reducing field at said input transducer,

said apparatus being free of acoustic feedback between said output transducer and said input transducer that supports oscillatory signals in said apparatus that impairs active noise reduction,

said apparatus being free of any other input transducer capble of providing a transduced input signal to said adaptive filter,

wherein said adaptive filter processes the signal on its input in accordance with a predictive algorithm so that said noise reducing field is of nearly equal magnitude and opposite phase relative to the noise field then at said input transducer in the absence of said noise reducing field.

2. Active noise reducing apparatus in accordance with claim 1 wherein said input transducer comprises a microphone and said output transducer comprises a loudspeaker driver.

3. Active noise reducing apparatus in accordance with claim 1 wherein said adaptive filter processes said transduced input signal in accordance with an estimate-maximize algorithm.

4. Active noise reducing apparatus in accordance with claim 1 wherein said adaptive filter processes said transduced input signal in accordance with a gradient-based algorithm.

5. Active noise reducing apparatus in accordance with claim 1 wherein said adaptive filter includes an estimator having an input and an output that provides said transduced signal,

a combiner having first and second inputs and an output coupled to the input of said estimator,

said first input being said input of said adaptive filter,

and feedback circuitry intercoupling said second input and the output of said estimator.

6. Active noise reducing apparatus in accordance with claim 1 wherein said adaptive filter includes an estimator having an input and an output that provides said transduced signal,

a combiner having first and second inputs and an output coupled to the input of said estimator,

said first input being said input of said adaptive filter,

and feedback circuitry intercoupling said second input and the output of said estimator.

7. Active noise reducing apparatus in accordance with claim 5 wherein said adaptive filter processes said transduced input signal in accordance with an estimate-maximize algorithm.

8. Active noise reducing apparatus in accordance with claim 6 wherein said adaptive filter processes said transduced input signal in accordance with an estimate-maximize algorithm.

9. Active noise reducing apparatus in accordance with claim 5 wherein said adaptive filter processes said transduced input signal in accordance with a gradient-based algorithm.

10. Active noise reducing apparatus in accordance with claim 6 wherein said adaptive filter processes said transduced input signal in accordance with a gradient-based algorithm.

11. A method of active noise reducing which method includes the steps of,

transducing with a single input transducer a sound field including a noise field at a first location to provide a transduced input signal,

adaptively filtering only said transduced input signal to provide a noise reducing electrical signal,

transducing said noise reducing electrical signal to provide a transduced noise-reducing signal at a second location to create a noise-reducing field at said first location,

and preventing acoustic feedback between said second location and said first location that supports oscillatory signals that impairs active noise reduction,

and further including adaptively filtering said transduced input signal in accordance with a predictive algorithm so that said noise reducing field is of nearly equal magnitude and opposite phase relative to the noise field then at said first location in the absence of said noise reducing field.

12. A method of active noise reducing in accordance with claim 11 wherein the step of adaptively filtering said transduced input signal in accordance with a predictive algorithm includes adaptively filtering said transduced input signal in accordance with a gradient-based algorithm.

13. A method of active noise reducing in accordance with claim 11 wherein the step of adaptively filtering said transduced input signal in accordance with a predictive algorithm includes adaptively filtering said transduced input signal in accordance with an estimate-maximize algorithm.