초록 ▼

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 loudspe

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').

대표청구항 ▼

1. A method of attenuating, in a desired location, a primary vibration entering that location from a primary source of vibration, which method comprises injecting into that location a secondary vibration of such waveform shape and amplitude that it will at least partially cancel the effect of the pr

1. A method of attenuating, in a desired location, a primary vibration entering that location from a primary source of vibration, which method comprises injecting into that location a secondary vibration of such waveform shape and amplitude that it will at least partially cancel the effect of the primary vibration in the desired location, the secondary vibration being generated by an amplifying/phase-shifting feedback loop linking a vibration-sensing transducer means, receiving both the secondary and primary vibrations and a closely proximate vibration-transmitting transducer means serving as the source of the secondary vibration, wherein the vibration-sensing transducer means is a directional microphone arranged to monitor both the primary and the secondary vibrations but to be less sensitive to the generated secondary vibration than to the primary vibration and the output from the vibration-transmitting transducer means is adjusted so that (a) the waveform shape of the secondary vibration generated by the said loop is the waveform shape which would be capable of cancelling the primary vibration at the location of the directional microphone and (b) the amplitude of said waveform is such that the at least partial cancellation produced by coaction between the secondary and primary vibrations, occurs at a position within the location which is spaced from the vibration-transmitting transducer means by a distance greater than the distance between the said directional microphone and the vibration-transmitting transducer means. 2. A method of attenuating, in a desired location, a primary vibration entering that location from a primary source of vibration, which method comprises injecting into that location a secondary vibration of such waveform shape and amplitude that it will at least partially cancel the effect of the primary vibration in the desired location, the secondry vibration being generated by an amplifying/ phase-shifting feedback loop, linking a vibration-sensing transducer means receiving both the secondary and primary vibrations and a closely proximate vibration-transmitting transducer means serving as the source of the secondary vibration, wherein the the vibration-sensing transducer means comprises a pair of microphones one of which is more sensitive to the secondary vibration than to the primary vibration than is the other of the pair, the output from the vibration-transmitting transducer means being adjusted so that (a) the waveform shape of the secondary vibration generated by the said loop is the waveform shape which would be capable of cancelling the primary vibration at the location of the said other microphone of the pair and (b) the amplitude of said waveform is such that the at least partial cancellation, produced by coaction between the secondary and primary vibrations, occurs at a position within the location which is spaced a greater distance from the vibration-transmitting transducer means than the distance between said other microphone and the said vibration-transmitting transducer means. 3. A method as claimed in claim 2, in which the amplitude of the secondary vibration is adjusted to produce a null at a further vibration-sensing transducer disposed in the said location. 4. A method as claimed in claim 3, in which the amplitude of the secondary vibration is automatically adapted on a trial and error basis to achieve a minimum output from said further vibration-sensing transducer. 5. A method as claimed in claim 1, in which the angle of the directional microphone is set relative to the vibration-transmitting transducer means and the primary source is adjusted to achieve optimum cancellation at the said position within the said location. 6. A method as claimed in claim 2, characterised in that both microphones of the pair receive both primary and secondary vibrations, but said other microphone of the pair is further from the vibration-transmitting transducer than is said one microphone of the pair. 7. A method as claimed in claim 2, wherein said one microphone of the pair is located inside a housing of the vibration-transmitting transducer means where it is sensibly screened from the primary vibration. 8. Apparatus for nulling a primary vibration in a selected location by using a specifically generated secondary vibration fed to the location, which apparatus comprises a vibration-sensing transducer means to sense both the primary and secondary vibrations, a vibration-transmitting transducer feeding the secondary vibration to the vibration-sensing transducer means and connected therewith in a phase-inverting feedback loop, characterised in that said vibration-sensing transducer means comprising two vibration-sensing transducers provided to sense the primary and secondary vibrations adjacent to the vibration-transmitting transducer in two different ratios, and means is provided to control the amplitude of a vibration generated by the vibration-transmitting transducer so that it is projected into the said location and there produces, with the primary vibration, a null of vibration energy, the means to control the amplitude of the secondary vibration transmitted to the said location including means to adjust the ratio if the signals fed from the two vibration-sensing transducers to the feedback loop. 9. Apparatus as claimed in claim 8, in which one of the vibration-sensing transducers is positioned where it will sense substantially only the secondary vibration.