Isao Kakuhari

Active noise control system

An active noise control system is provided which cancels noise using a sound which is radiated from a speaker which is driven by an output from an adaptive notch filter. The system uses the output signals from an adder or a cosine wave simulation signal and a sine wave simulation signal, an error signal or an output signal from a microphone and a compensated signal from the adder or a signal representative of an acoustic transmission of an output from the adaptive notch filter to the microphone is available with initial transmission characteristics in accordance to update the filter coefficients of the adaptive notch filter. This configuration allows the system to operate with stability even if modify the acoustic transmission characteristics with time or under certain circumstances, if a significant value of the incoming external noise exists. The system also prevents the over-compensation for a sound at the ears of a passenger in a vehicle, whereby an ideal noise reduction effect is provided.