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Active noise control

  • US 4,876,722 A
  • Filed: 05/13/1988
  • Issued: 10/24/1989
  • Est. Priority Date: 02/14/1986
  • Status: Expired due to Term
First Claim
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1. An active noise control system for reducing the amount of noise propagated through a duct, comprising:

  • a microphone incorporated in a wall of said duct, and operative for detecting the sound of the propagated noise;

    a source of anti-sound mounted substantially at the center of a transverse cross-section of said duct; and

    a control circuit responsive to the magnitude of the sound detected by the microphone for driving the anti-sound source to substantially suppress first transverse mode excitation in said duct.

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