Toshio Inoue

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.

Active control system for low-frequency road noise combined with an audio system

An active control system for low-frequency road noise in automobiles combined with an audio system is developed as a commercial application for the first time in the world, and installed in a station wagon. The purpose of this paper is to provide an outline of the system and describe the newly developed cost-reduction technology used for it, since the reduction of system costs is a major reason that active noise control technology could successfully be applied in a commercial product. The methods used to reduce costs include utilization of feedback control, implementation by analogue circuits, and common use of audio system speakers. This system reduces low-frequency road noise in the front seat by about 10 dB and improves audio system listening experience while driving.