Acoustic abatement method and apparatus
First Claim
1. A method for attenuating a predetermined range of frequencies within an acoustic wave propagating along different vectors through a medium, comprising the steps of:
- generating an anti wave limited to only said predetermined range of frequencies and of mirror symmetry with respect to said acoustic wave,propagating said anti wave in said medium along a given vector which is at a skew with respect to one of said different vectors,altering a vector of at least one of said waves to produce substantially coinciding vectors of propagation only for the predetermined range of frequencies, andaligning the wavefront of at least one of said waves to produce substantially coinciding wavefronts.
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Accused Products
Abstract
An acoustic receiver, amplifier and transmitter generate an anti wave which is in-phase and of mirror symmetry with respect to a propagating acoustic wave. Coherent propagation means such as an acoustic duct of particular dimensions redirects and/or converts the acoustic wave and the anti wave, which otherwise propagate with incremental wavefronts at different vectors, into plane waves which are superimposed to create wave interference which itself propagates. For noise of high sound pressure level such as created by a gas turbine engine, the acoustic transmitter comprises a modulated gas flow speaker coupled to one or more bleed ports which supply gas at one or more pressures offset from ambient pressure.
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Citations
39 Claims
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1. A method for attenuating a predetermined range of frequencies within an acoustic wave propagating along different vectors through a medium, comprising the steps of:
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generating an anti wave limited to only said predetermined range of frequencies and of mirror symmetry with respect to said acoustic wave, propagating said anti wave in said medium along a given vector which is at a skew with respect to one of said different vectors, altering a vector of at least one of said waves to produce substantially coinciding vectors of propagation only for the predetermined range of frequencies, and aligning the wavefront of at least one of said waves to produce substantially coinciding wavefronts. - View Dependent Claims (2, 3, 4, 5)
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6. A method for attenuating an acoustic wave propagating along different vectors through a medium, comprising the steps of:
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detecting the acoustic wave to produce an anti wave signal corresponding thereto, propagating in said medium along a given vector which is at a skew with respect to one of said different vectors an anti wave of mirror symmetry with respect to said acoustic wave by producing a flow of the medium at a pressure continuously offset from the ambient pressure of the medium, and modulating the flow in accordance with variations in said signal, altering a vector of at least one of said waves to produce substantially coinciding vectors of propagation, and aligning the wavefront of at least one of said waves to produce substantially coinciding wavefronts. - View Dependent Claims (7)
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8. A system for attenuating an acoustic wave propagating through a medium which is sufficiently unconfined to allow different vectors of propagation of the acoustic wave, comprising:
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duct means having a pair of spaced apertures each open to said medium and a hollow passageway therebetween, the duct means being positionable to cause one of said apertures to intersect and direct the propagating acoustic wave through the passageway toward the other of said apertures, said passageway having a cross section of reduced size with respect to the cross section of the medium outside of the duct means and producing a duct cut-off frequency corresponding to the lowest order acoustic mode of propagation to confine the acoustic wave to a plane wavefront for frequencies below the duct cut-off frequency and of a predetermined vector of propagation; receiver means for generating a signal corresponding to the propagating acoustic wave; transmitter means responsive to said signal for generating in said passageway an interference wave of opposite pressure variation with respect to the acoustic wave and having a plane wavefront for frequencies below the duct cut-off frequency and of a predetermined vector of propagation to produce a propagating cancellation effect; and low pass filter means connecting said receiver means to said transmitter means and passing signals less than the duct cut-off frequency. - View Dependent Claims (9, 10, 11)
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12. A system for attenuating an acoustic wave propagating through a medium, comprising:
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duct means having a pair of spaced apertures each open to said medium and a hollow passageway therebetween, one of said apertures being positionable to intersect the propagating acoustic wave to cause the acoustic wave to propagate through the passageway toward the other of said apertures, said passageway having a cross section of predetermined size to confine the acoustic wave to a wavefront of predetermined shape, said duct means allowing a backward wave to propagate through the passageway in a direction opposite to the propagating acoustic wave; means for generating an interference wave having a wavefront of said predetermined shape including receiver means contiguous with the passageway and responsive to said acoustic wave for generating a signal corresponding to the propagating acoustic wave, diaphragm means movable in response to said signal to produce at a transmitter output an opposite pressure variation with respect to the acoustic wave, mounting means locating said transmitter output generally facing said other aperture to direct the interference wave through said passageway with a vector direction toward said other aperture and away from said one aperture, and means for preventing the backward wave from producing at the transmitter output any pressure variation. - View Dependent Claims (13, 14, 15)
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16. A system for attenuating an acoustic wave propagating through a medium which is sufficiently unconfined to allow different vectors of propagation of the acoustic wave, comprising:
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duct means having a pair of spaced apertures each open to said medium and a hollow passageway therebetween with central core means located within a center area of the passgeway, the duct means and the central core means defining therebetween a surrounding passageway, the duct means being positionable to cause one of said apertures to intersect and direct the propagating acoustic wave through the surrounding passageway toward the other of said apertures, said surrounding passageway having a cross section of predetermined size to confine the acoustic wave to a wavefront of predetermined shape and of a predetermined vector of propagation; receiver means for generating a signal corresponding to the propagating acoustic wave; and transmitter means including diaphragm means movable in response to said signal to produce at a transmitter output a pressure variation related thereto, and transmitter mounting means for locating said transmitter output within said central core means and oriented to disperse the pressure variations into the surrounding passageway to generate an interference wave of opposite pressure variation with respect to the acoustic wave and having a wavefront of the same predetermined shape and predetermined vector of propagation to produce a propagating cancellation effect. - View Dependent Claims (17, 18, 19)
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20. In a gas breathing engine having rotating machinery creating a pressure gradient in a passageway which opens external to the engine and undesirably creating in said passageway acoustic noise which unless attenuated will propagate external to the engine, apparatus for attenuating the acoustic noise, comprising:
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receiver means for detecting said acoustic noise and generating an audio signal corresponding thereto, modulated gas flow speaker means having a speaker inlet for receiving gas at a pressure offset from ambient pressure at a speaker outlet, and a modulator for coupling said speaker inlet to said speaker outlet and responsive to an audio signal for modulating a flow of the gas, bleed port means located in said passageway and open to gas at said offset pressure, tubing means connecting said bleed port means to said speaker inlet for supplying the gas to said modulator, anti noise means coupling said receiver means to said modulator to produce at said speaker outlet an interference wave of mirror symmetry with respect to said acoustic noise, and coherent propagation means associated with said speaker outlet and said passageway for superimposing the acoustic noise and the interference wave to produce interference cancellation therebetween. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28)
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29. A system for attenuating an acoustic wave propagating through a medium, comprising:
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source means including receiver means for detecting said acoustic wave, transmitter means responsive to said receiver means for producing an anti wave which interferes with said acoustic wave to produce a cancellation effect, and time delay means for varying the transmission time of the source means to change the position of said anti wave in said medium, sensing means for sensing a condition which indicates misalignment between the anti wave and the acoustic wave which were initially aligned, and correction means responsive to said sensing means for automatically varying said time delay means to again align the anti wave with the acoustic wave. - View Dependent Claims (30, 31)
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32. A system for attenuating an acoustic wave propagating through a medium, comprising:
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receiver means positionable to intersect the acoustic wave for generating a receiver signal corresponding thereto, transmitter means spaced from said receiver means and responsive to an amplified signal for generating an interference wave which propagates toward an interference zone spaced away from the receiver means and the transmitter means, generation of the interference wave undesirably creating a traveling wave which propagates to said receiver means and produces a false signal not resulting from the acoustic wave, and amplifier means having an amplifier input coupled to said receiver means and an amplifier output coupled to said transmitter means for amplifying the receiver signal to generate the amplified signal, including feedback means generating a feedback signal having a time delay corresponding to the propagation time of the traveling wave for cancelling the false signal produced when the traveling wave reaches the receiver means. - View Dependent Claims (33, 34)
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35. A system for attenuating an acoustic wave propagating through a medium, comprising:
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a plurality of separate ducts surrounding a central core and each having a separate passageway with an opening contiguous with the central core; receiver means for generating a signal corresponding to an acoustic wave propagating through at least one of the separate passageways; and transmitter means located in said central core and responsive to said signal for generating an interference wave which propagates through all of the contiguous opening into the plurality of separate passageways to produce cancellation between the interference wave and the acoustic wave propagating in the associated passageway. - View Dependent Claims (36, 37, 38, 39)
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Specification