Hybrid active silencer
First Claim
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1. Acoustic attenuation apparatus for a duct guiding an acoustic wave propagating therethrough, comprising:
- a silencer for passively attenuating the acoustic wave in the duct, said silencer comprising acoustically absorptive material defining a flow path through the duct; and
a sound source within said silencer for injecting a cancelling acoustic wave into said flow path, said sound source being between and spaced from the ends of said silencer to isolate said sound source from duct reflections, to provide hybrid active/passive combined attenuation,wherein said silencer has a central splitter wall section, and comprising a pair of said sound sources, one on each side of said splitter.
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Abstract
Acoustic attenuation apparatus (2) is provided for a duct (4) guiding an acoustic wave propagating (6) therethrough. A silencer (8) is provided for passively attenuating the acoustic wave in the duct, and a cancelling speaker (32) is provided within the silencer. The combination provides hybrid active/passive combined attenuation. Various rectangular and circular structures are disclosed, together with multi-path and multi-speaker arrangements.
118 Citations
23 Claims
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1. Acoustic attenuation apparatus for a duct guiding an acoustic wave propagating therethrough, comprising:
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a silencer for passively attenuating the acoustic wave in the duct, said silencer comprising acoustically absorptive material defining a flow path through the duct; and a sound source within said silencer for injecting a cancelling acoustic wave into said flow path, said sound source being between and spaced from the ends of said silencer to isolate said sound source from duct reflections, to provide hybrid active/passive combined attenuation, wherein said silencer has a central splitter wall section, and comprising a pair of said sound sources, one on each side of said splitter.
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2. Acoustic attenuation apparatus for a duct guiding an acoustic wave propagating therethrough, comprising:
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a silencer for passively attenuating the acoustic wave in the duct, said silencer comprising an acoustically absorptive wall structure extending parallel to the acoustic propagation flow path through the duct; and a sound source disposed in said silencer wall structure for injecting a cancelling acoustic wave into said flow path to actively attenuate said acoustic wave, said sound source being between and spaced from the ends of said wall structure to isolate said sound source from duct reflections, to provide hybrid active/passive combined attenuation, wherein said wall structure is packed with acoustically absorptive packing material and has a T-shaped space formed therein with the cross-bar of the T extending parallel to said flow path and the central stem of the T extending from said cross-bar laterally toward said flow path, said packing material being between said cross-bar of the T and said flow path, said sound source being disposed in said lateral central stem of the T and facing said flow path.
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3. Acoustic attenuation apparatus for a duct guiding an acoustic wave propagating therethrough, comprising:
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a silencer for passively attenuating the acoustic wave in the duct, said silencer comprising an acoustically absorptive wall structure extending parallel to the acoustic propagation flow path through the duct; and a sound source disposed in said silencer wall structure for injecting a cancelling acoustic wave into said flow path to actively attenuate said acoustic wave, said sound source being between and spaced from the ends of said wall structure to isolate said sound source from duct reflections, to provide hybrid active/passive combined attenuation, wherein said silencer wall structure comprises a central splitter wall section defining first and second said flow paths on laterally opposite sides thereof. - View Dependent Claims (4, 5, 6, 7, 8, 9, 10)
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11. Acoustic attenuation apparatus for a duct guiding an acoustic wave propagating therethrough, comprising:
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a silencer for passively attenuating the acoustic wave in the duct, said silencer comprising an acoustically absorptive wall structure extending parallel to the acoustic propagation flow path through the duct, a sound source disposed in said silencer wall structure for injecting a cancelling acoustic wave into said flow path to actively attenuate said acoustic wave, said sound source being between and spaced from the ends of said wall structure to isolate said sound source from duct reflections, to provide hybrid active/passive combined attenuation; and a thin protective layer of acoustically transmissive material covering said sound source and resisting corrosion and transmitting low frequency acoustic waves less than about 500 Hz.
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12. Acoustic attentuation apparatus for a duct guiding an acoustic wave propagating therethrough, comprising:
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a silencer for passively attenuating the acoustic wave in the duct, said silencer comprising an acoustically absorptive wall structure extending parallel to the acoustic propagation flow path through the duct; a sound source disposed in said silencer wall structure for injecting a cancelling acoustic wave into said flow path to actively attenuate said acoustic wave, said sound source being between and spaced from the ends of said wall structure to isolate said sound source from duct reflections, to provide hybrid active/passive combined attenuation; and a fluid conduit cooling coil wrapped around said sound source.
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13. Acoustic attenutation apparatus for a round duct guiding an acoustic wave propagating therethrough, comprising:
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a cylindrical bullet-like silencer of acoustically absorptive material for passively attenuating the acoustic wave in the duct, said silencer being split into two segments, a forward segment and a rearward segment separated by a gap therebetween; and a sound source in said rearward segment of said acoustically absorptive bullet-like silencer and facing toward said forward segment of said acoustically absorptive bullet-like silencer across said gap for injecting a cancelling acoustic wave toward said acoustically absorptive forward segment and laterally therearound and into said flow path, said sound source being between and spaced from the ends of said bulletlike silencer to isolate said sound source from duct reflections, to provide hybrid active/passive combined attenuation. - View Dependent Claims (14, 15, 16, 17, 18)
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19. Acoustic attenuation apparatus for a round duct guiding an acoustic wave propagating therethrough, comprising:
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a cylindrical silencer for passively attenuating the acoustic wave in the duct, said cylindrical silencer comprising an outer acoustically absorptive cylindrical wall structure extending parallel to the propagation path of the acoustic wave, and a central cylindrical bullet-like member of acoustically absorptive material spaced radially inwardly from said outer wall structure to define an annular flow path between said outer wall structure and said central bullet-like member, said central bullet-like member being split into two segments, a forward segment and a rearward segment separated by a gap therebetween; and a sound source in said rearward segment of said central bullet-like member and facing toward said forward segment across said gap for injecting a cancelling acoustic wave toward said forward segment and laterally therearound and into said annular flow path, said sound source being between and spaced from the ends of said silencer to isolate said sound source from duct reflections, to provide hybrid active/passive combined attenuation. - View Dependent Claims (20)
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21. Acoustic attenuation appartus for a round duct guiding an acoustic wave propagating therethrough, comprising:
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a cylindrical bullet-like silencer of acoustically absorptive material for passively attenuating the acoustic wave in the duct, said silencer being split into two segments, a forward segment and a rearward segment separated by a gap therebetween; and a sound source in said forward segment of said acoustically absorptive bullet-like silencer and facing toward said rearward segment of said acoustically absorptive bullet-like silencer across said gap for injecting a cancelling acoustic wave toward said rearward segment and laterally therearound and into said flow path, said sound source being between and spaced from the ends of said bullet-like silencer to isolate said sound source from duct reflections, to provide hybrid active/passive combined attenuation. - View Dependent Claims (22, 23)
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Specification