Method and apparatus for the active reduction of compression waves

• US 5,224,168 A
• Filed: 05/08/1991
• Issued: 06/29/1993
• Est. Priority Date: 05/08/1991
• Status: Expired due to Fees

• Current Assignee: SRI International, Inc.
• Original Assignee: SRI International, Inc.
• Inventors: Mason, V. Bradford, Martinez, J. Raul
• Primary Examiner(s): Isen, Forester W.
• Application Number:
  US07/697,154
• Time in Patent Office: 783 Days
• Field of Search: 381/71, 381/94
• US Class Current: 381/71.8
• CPC Class Codes: G10K 11/17853 of the filter
• 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 2210/101 One dimensional
• CPC Class Codes: G10K 2210/121 Rotating machines, e.g. engines, turbines, motors; Periodic or quasi-periodic signals in general
• CPC Class Codes: G10K 2210/3045 Multiple acoustic inputs, single acoustic output
• CPC Class Codes: G10K 2210/3046 Multiple acoustic inputs, multiple acoustic outputs
• CPC Class Codes: G10K 2210/3216 Cancellation means disposed in the vicinity of the source

Abstract

An apparatus for reducing noise characterized by a number of input microphones arranged near an undesired noise source, a signal processor coupled to the input microphones and operative to develop a number of output signals from the input signals, and a number of speakers coupled to the output signals of the signal processor to produce anti-noise within a designated quiet zone. Each of the speakers derives a portion of its signal from each of the input microphones so that each output transducer has the maximum amount of information concerning the noise to be canceled. The method of the invention is characterized by the steps of detecting compression waves at a number of detection locations within a medium, and developing a number of complementary signals utilizing all of the detected compression wave information.

Claims

1. An apparatus for reducing undesired compression waves in a quiet zone of a medium comprising:

a plurality of input transducers sensitive to undesired compression waves outside of a quiet zone of a medium and operative to produce a plurality of input signals in response thereto;

means for processing said plurality of input signals to produce a plurality of output signals, wherein each of said output signals is derived from each of said input signals such that said apparatus includes a plurality of channels at least equal to the product of the number of said input signals and the number of said output signals; and

a plurality of output transducers responsive to said plurality of output signals and operative to produce complementary compression waves in said medium which combine with said undesired compression waves in said quiet zone.

2. An apparatus as recited in claim 1 wherein said means for processing further includes feedback reduction means for reducing feedback between said output transducers and said input transducers.

3. An apparatus as recited in claim 2 wherein said feedback reduction means is responsive to more than one of said output signals.

4. An apparatus for reducing noise comprising:

a plurality of input transducers exposed to an unwanted noise wavefront prior to said unwanted wavefront entering a quiet zone, said input transducers developing a plurality of input signals in response thereto;

signal processing means coupled to said plurality of input transducers and operative to develop at least one output signal which is derived from each of said input signals, wherein said signal processing means has a number of channels at least equal to the product of the number of said input signals and the number of said output signals; and

output transducer means coupled to said signal processing means for converting at least one output signal into a complementary anti-noise wavefront which is substantially 180°

out of phase with said noise wavefront, wherein said complementary anti-noise wavefront and said unwanted noise wavefront combine in said quiet zone.

5. An apparatus for reducing noise as recited in claim 4 wherein said signal processing means develops a plurality of output signals each of which is derived from more than one input signal and wherein said output transducer means includes a plurality of output transducers responsive to said output signals.

6. An apparatus for reducing noise as recited in claim 5 wherein said signal processing includes at least one forward filter means associated with each channel, where each filter has an input coupled to an input signal and an output developing a portion of an output signal.

7. An apparatus for reducing noise as recited in claim 6 further comprising a first plurality of summation means having inputs coupled to a plurality of said outputs of said forward filter means and each having an output coupled to one of said output transducers.

8. An apparatus for reducing noise as recited in claim 7 wherein said signal processing means further includes a plurality of reverse filters and a second plurality of summation means, said second plurality of summation means having inputs coupled to said input signals and to a plurality of said outputs of said first plurality of summation means by said plurality of reverse filters, said second plurality of summation means having outputs coupled to a plurality of inputs of said forward filter means.