Abstract: An active noise eliminating system comprises microphones for detecting residual noise, speakers for generating noise elimination sound for interference with the residual noise, a noise generating condition sensor for generating noise condition, a controller for generating noise elimination signals inputted to the speakers and determined by the detected residual noise signals and the detected noise condition signal in accordance with a control algorithm including transfer functions between the speakers and microphones respectively. The transfer functions are updated on the basis of a test signal generated when noise sound diverges.

Abstract: An apparatus for reducing periodical noises transmitted from a noise source into a vehicle passenger compartment. The apparatus comprises control sound sources for producing control sounds in the vehicle passenger compartment, residual noise sensors for detecting the residual noises in the vehicle passenger compartment, transfer function filters modeled on transfer function between the control sound sources and the residual noise sensors, and adaptive digital filters having variable filter coefficients. A reference signal is produced in the form of a series of impulses having the same period as the noises. The transfer function filters are convoluted with the reference signal to produce reference processed signals. The adaptive digital filters are convoluted with the reference signal to generate drive signals to drive the control sound sources.

Abstract: An apparatus for active reduction of noises transmitted from a noise source into a space. The active noise reduction apparatus comprises residual noise sensors for detecting the residual noises in the space. A reference signal is produced based upon the noise generating condition of the noise source. The reference signal is used, along with the detected residual noises, to drive control sound sources so as to reduce the noises in the space. A filter is adjusted to correspond to acoustic transfer characteristics between the control sound sources and the residual noise sensors. An identification sound is generated to correspond to the background noise level detected in the space and to the spectral distribution of the noises transmitted into the space. The coefficients of the filter are updated according to acoustic transfer characteristics between the control sound sources and the residual noise sensors.

Abstract: An apparatus for reducing noise for an interior of enclosed space, e.g., a vehicular compartment using an FIR adaptive digital filter is disclosed in which a control circuit is provided which outputs drive signals to a plurality of loud speakers which generate control sounds to interfer with a noise sound propagated in the interior so that a performance function including terms of residual noise signals output from residual noise signal detecting microphones and drive signals to the loud speakers is minimized and contributivity of the drive signals to the performance function is changed according to an occurrence of divergence in the noise reducing apparatus.

Abstract: In an apparatus for reducing noises in a space, signals related to noise generating conditions of a plurality of noise sources are detected, a signal component of the detected signals is selected on the basis of determination of which signal component is predominant over the other signal component in the noises in the space, and the selected signal component is filtered through adaptively determined filter coefficients to output drive signals to control sound source, the filter coefficients being updated through a control algorithm so as to reduce a residual noise of a residual noise detector such as microphones. The signal components to be selected include a signal component having a relatively high auto-correlated function characteristic and a signal component having a random characteristic.