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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

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.

대표청구항 ▼

An apparatus for cancelling of noise or vibrations, comprising: means for producing an electrical error signal representative of the sum of the instantaneous amplitudes of an unwanted periodic acoustic signal and a cancelling acoustic signal; filtering means for filtering the electrical error signal

An apparatus for cancelling of noise or vibrations, comprising: means for producing an electrical error signal representative of the sum of the instantaneous amplitudes of an unwanted periodic acoustic signal and a cancelling acoustic signal; filtering means for filtering the electrical error signal to produce an electrical cancelling signal comprising the filtered electrical error signal; means responsive to the electrical cancelling signal to produce the cancelling acoustic signal for cancelling the unwanted periodic acoustic signal; and control signal generating means for generating a control signal, harmonically related to the unwanted periodic acoustic signal; wherein the filtering means includes a tunable bandpass filter means for filtering the electrical error signal, the filter means being tuned, in response to the control signal, so as to maintain within its passband a frequency harmonically related to the unwanted periodic acoustic signal.