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Active noise cancelling apparatus

  • US 5,499,301 A
  • Filed: 10/20/1994
  • Issued: 03/12/1996
  • Est. Priority Date: 09/19/1991
  • Status: Expired due to Fees
First Claim
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1. An active noise cancelling apparatus for actively controlling high frequency cyclic noise generated by a rotary machine, where noise is apt to externally leak from an opening portion of a machine chamber storing the rotary machine driven by an A.C. power supply, the apparatus comprising:

  • sound detecting means, provided in the vicinity of the opening portion, for detecting noise generated by the rotary machine;

    fundamental wave component extracting means for extracting a fundamental wave component of rotation frequency of the rotary machine, from a sound signal of the noise detected by the sound detecting means;

    periodic signal generating means for generating a periodic signal correlative to the fundamental wave component extracted by the fundamental wave component extracting means;

    periodic signal outputting means for outputting a predetermined periodic signal by means of comparing a phase of the periodic signal generated by the periodic signal generating means with a phase of the fundamental wave component;

    uncancelled sound extracting means for extracting noise having been not cancelled, after a control signal is outputted from control signal outputting means, excluding the fundamental wave component;

    sound source waveform generating means for forming a harmonics component from the signal outputted by the periodic signal outputting means, the harmonics component being a sound source waveform which has a phase opposite to and a same amplitude with a sound source signal detected by the sound detecting means;

    control signal generating means for correcting a control signal outputted from the sound source waveform generating means, based on a signal from the uncancelled sound extracting means and for generating the corrected signal in a feedback manner; and

    output means for outputting the control generated from the control signal correcting means.

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