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Active acoustic attenuation system for higher order mode non-uniform sound field in a duct

  • US 4,815,139 A
  • Filed: 03/16/1988
  • Issued: 03/21/1989
  • Est. Priority Date: 03/16/1988
  • Status: Expired due to Term
First Claim
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1. An active attenuation system for attenuating an undesired elastic wave propagating in an elastic medium, said elastic wave having non-uniform pressure distribution in said medium at a given instant in time along a direction transverse to the direction of propagation, such that said wave has a plurality of portions along the transverse direction including at least one positive pressure portion and at least one negative pressure portion,a plurality of output transducers, one for each of said positive and negative pressure portions of said undesired elastic wave, said output transducers introducing a plurality of cancelling elastic waves into said medium,a plurality of error transducers, one for each of said positive and negative pressure portions of said undesired elastic wave, said error transducers sensing the combined said undesired elastic wave and said cancelling elastic waves, and providing a plurality of error signals,a plurality of adaptive filter models, one for each of said positive and negative pressure portions of said undesired elastic wave, each said model having an error input from a respective said error transducer and outputting a correction signal to a respective said output transducer to introduce the respective said cancelling elastic wave, such that each said portion of said undesired elastic wave has its own set of an adaptive filter model, output transducer, and error transducer.

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