Hitachi, Ltd.

Nissan Motor Company Limited

Satoshi Hasegawa

Hiroyuki Saito

Noriharu Sato

Mitsuru Nakamura

Mitsuhide Sasaki

Osamu Igarashi

Toshiyuki Tabata

An automatic sound suppression system is automatically disengaged whenever noise in an area and generated counter noise deviate in their reverse phase relationship or if the amplitude of the counter noise deviates from that of the noise. The system can also be automatically disengaged whenever divergence prediction means predicts that sounds of the noise and the counter noise diverge or whenever divergence prediction means predict that sounds of the noise and the counter noise are about to diverge. The system can also operate as a vibration reducing apparatus which is also automatically disengaged whenever divergence prediction means predicts that a vibration and a generated countervibration diverge.

Apparatus for reducing noise in a closed space having divergence detector

When noise is caused by the mechanical vibration propagated from the engine, the microprocessor calculates from the vibration frequency of the engine the secondary sound signal which is in antiphase with the noise and which is thus able to cancel out the noise, and supplies it to the loudspeaker which then emanates the secondary sound according to this signal. At this time,the divergence detection circuit monitors the incoming secondary sound signal, and when the secondary sound signal is remarkably increased, it decides that the noise is increased, and automatically stops the secondary sound output from the loudspeaker. Therefore, it can be prevented that the noise is reversely increased by the secondary sound.

Noise reduction apparatus

Growing community of inventors

Yamato, Japan

Satoshi Hasegawa