Noise reduction system
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United States of America Patent
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Jun 10, 1997
Grant Date -
N/A
app pub date -
May 26, 1994
filing date -
Jul 30, 1991
priority date (Note) -
Expired
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Abstract
A system for reducing periodic noise, which includes a plurality of harmonically related noise signals, comprises an actuator for producing a canceling acoustic signal, a sensor for detecting a residual noise signal, a synchronizing signal generator and processing circuitry. The processing circuitry comprises a plurality of tunable harmonically related band pass filters, a tuning signal generator and a summer which sums the outputs of the filters. The tuning signal generator receives the synchronizing signal from the synchronizing signal generator and outputs the tuning signals to the band pass filters. As the frequency of the synchronizing signal changes, the tuning signal generator causes the tunable filters to track harmonics of the noise to be canceled. After summing by the summer and suitable amplification, the outputs from the filters are used to drive the actuator so as to reduce the residual noise detected by the sensor.
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