METHOD AND APPARATUS FOR LOW FREQUENCY ACTIVE ATTENUATION

摘要

PCT No. PCT/GB82/00250 Sec. 371 Date Apr. 11, 1983 Sec. 102(e) Date Apr. 11, 1983 PCT Filed Aug. 10, 1982 PCT Pub. No. WO83/00580 PCT Pub. Date Feb. 17, 1983.A low frequency attenuation method based on the virtual earth system has the driver feeding cancelling waveforms into a partially closed volume which contains the microphone of the virtual earth feed-back loop. The volume preferably has a maximum dimensions which lies between one third and one seventh of the wavelength of the highest frequency to be nulled. An outlet port of the volume can be tuned to the center frequency of the band of frequencies to be nulled.