Active noise cancelling apparatus

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 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 noise 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 fundamental wave component extracting 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, wherein respective sound source waveforms of an electromagnetic sound detected from the A.C. power supply and a rotation sound of the rotary machine detected by the sound detecting means are synthesized so as to form a final control noise-cancelling waveform;
• and
• output means for outputting the control generated from the control signal correcting means.

An active noise cancelling apparatus for reducing noise emanating from a rotary machine driven in synchronism with a fundamental frequency comprising:

• a microphone provided at a location where said noise is desired to be reduced;
• a band-pass filter connected to said microphone in order to extract said fundamental frequency from the noise;
• a sound waveform generating circuit connected to said band-pass filter for generating signals representing harmonic sounds of said fundamental frequency with half-wave phase differences;
• a speaker provided adjacent to said rotary machine;
• a driving circuit connected to said speaker and said sound waveform generating circuit for controlling said speaker to generate said harmonic sounds in accordance with the signals output from said sound waveform generating circuit;
• a high pass filter connected to said microphone in order to detect harmonic components of sounds occurring at said location other than that having said fundamental frequency;
• and
• a silencing error adaptive filter connected to said driving circuit and said high pass filter to control said driving circuit to enhance cancellation of said noise at said location by said harmonic sound generated from said speaker in accordance with a transfer characteristic function rectified in accordance with said harmonic component detected by said high pass filter.