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Noise cancellation apparatus

  • US 5,825,897 A
  • Filed: 08/18/1997
  • Issued: 10/20/1998
  • Est. Priority Date: 10/29/1992
  • Status: Expired due to Term
First Claim
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1. A method for independently calibrating an open loop active noise reduction apparatus including a housing comprising a speaker to produce an acoustic anti-noise signal in the housing, a microphone to detect an external noise signal, an acoustical waveguide having zero phase shift over a desired bandwidth to isolate and direct the acoustic anti-noise signal from the microphone, and an amplitude adjustment means to calibrate the acoustic anti-noise signal to create a quiet zone in the housing for operation with an independent electrical assembly, wherein the apparatus is calibrated separately from the electrical assembly, the method comprising the steps of:

  • producing the external noise signal having a gain and phase response detected by the microphone in the housing;

    inputting an external noise signal received by the microphone through acoustic-electra processing means in the electrical assembly to produce an electrical anti-noise signal;

    transmitting to the speaker the electrical anti-noise signal having an equal gain and opposite phase response to the external noise signal detected by the microphone; and

    balancing the gain and phase response of the electrical anti-noise signal by the amplitude adjustment means located in the noise reduction apparatus to match the gain and phase response of the external noise signal to yield a theoretical zero in the quiet zone.

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