Active acoustic attenuation system for higher order mode non-uniform sound field in a duct
First Claim
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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Abstract
A system is provided for increasing the frequency range of an active acoustic attenuation system in a duct without increasing cut-off frequency fc of the duct or otherwise splitting or partitioning the duct into separate ducts or chambers. The frequency range is increased above fc to include higher order modes. A plurality of cancelling model sets are provided. Each transverse portion of the acoustic pressure wave has its own set of an adaptive filter model, cancelling speaker, and error microphone. A single input microphone may service all sets.
78 Citations
38 Claims
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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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4. In an active acoustic attenuation system for attenuating an acoustic wave in an acoustic system including an axially extending duct having an input for receiving an input acoustic wave and an output for radiating an output acoustic wave, said acoustic wave propagating axially through said duct, said duct having a higher order mode cut-off frequency fc, wherein acoustic frequencies below fc provide plane and uniform pressure acoustic waves transversely across said duct at a given instant in time, a method for increasing the frequency range of said active acoustic attenuation system without increasing fc or otherwise splitting said duct into separate ducts or partitioning said duct into separate chambers, comprising increasing said frequency range to include higher order modes wherein the acoustic wave has a plurality of portions extending transversely across said duct at a given instant in time including at least one positive pressure portion and at least one negative pressure portion, comprising:
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introducing a plurality of cancelling acoustic waves into said duct from a plurality of output transducers, one for each of said positive and negative pressure wave portions, for attenuating said output acoustic wave; sensing the combined said output acoustic wave and said cancelling acoustic waves with a plurality of error transducers, one for each of said positive and negative pressure wave portions, and providing a plurality of error signals; modeling said acoustic system with a plurality of adaptive filter models, one for each of said positive and negative pressure wave portions, 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 acoustic wave. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. In an active acoustic attenuation system for attenuating an acoustic wave in an acoustic system including an axially extending duct having an input for receiving an input acoustic wave and an output for radiating an output acoustic wave, said acoustic wave propagating axially through said duct, said duct having a higher order mode cut-off frequency fc, wherein acoustic frequencies below fc provide plane and uniform pressure acoustic waves transversely across said duct at a given instant in time, and wherein acoustic frequencies above fc provide a higher order mode such that said acoustic wave has N portions extending transversely across said duct at a given instant in time, where N≧
- 2, including at least one positive pressure portion and at least one negative pressure portion, a method for increasing the frequency range of said active acoustic attentuation system above fc, comprising;
outputting N acoustic waves into said duct from N output transducers, respectively, for attenuating said output acoustic wave; sensing the combined said output acoustic wave and said N acoustic waves from said N output transducers with N error transducers and providing N error signals, respectively; modeling said acoustic system with N adaptive filter models having error inputs from respective said error transducers and outputting N correction signals, respectively, to said N output transducers, to introduce said N acoustic waves, such that said N error signals approach respective given values. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23)
- 2, including at least one positive pressure portion and at least one negative pressure portion, a method for increasing the frequency range of said active acoustic attentuation system above fc, comprising;
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24. In an acoustic system including an axially extending duct having an input for receiving an input acoustic wave and an output for radiating an output acoustic wave, said acoustic wave propagating axially through said duct, said duct having a higher order mode cut-off frequency fc, such that said acoustic wave has N portions extending transversely across said duct at a given instant in time, where N is ≧
- 2, including at least one positive pressure portion and at least one negative pressure portion, an active acoustic attenuation system comprising;
N output transducers outputting N acoustic waves, respectively, for attenuating said output acoustic wave; N error transducers sensing the combined said output acoustic wave and said N acoustic waves from said N output transducers and providing N error signals, respectively; N adaptive filter models adaptively modeling said acoustic system, each model having an error input from a respective one of said N error transducers and outputting a correction signal to a respective one of said N output transducers to introduce a respective one of said N acoustic waves such that each of said N error signals approaches a given respective value. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38)
- 2, including at least one positive pressure portion and at least one negative pressure portion, an active acoustic attenuation system comprising;
Specification