| 摘要 |
PCT No. PCT/GB80/00201 Sec. 371 Date Jul. 15, 1981 Sec. 102(e) Date Jul. 15, 1981 PCT Filed Nov. 21, 1980 PCT Pub. No. WO81/01480 PCT Pub. Date May 28, 1981.Improved method and apparatus for the nulling of a primary vibration by the "active" method, based on the "virtual earth" system in which the output of a loudspeaker (3') is continually controlled by a feedback loop (1', 2' 3') to maintain a null at a microphone (1') disposed adjacent to the loudspeaker. In accordance with the invention the loop (1', 2', 3') is used as a generator for the correct waveform of the secondary vibration required to null the primary vibration, the amplitude at which the secondary vibration is projected into the primary vibration being increased to move the null point to the far field of the loudspeaker (3').
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