| 摘要 |
Primary vibrations (N), e.g. acoustic noise or vibration from a source there of such as a motor, are cancelled by secondary vibrations (C) produced by an actuator (2) driven by a controller (3) that i s responsive to an error signal (E) detected by a detector (4) and representative of the residual or difference between the primary and secondary vibrations. The controller samples the er- ror signal (E) during successive sampling periods determined by a synchronising signal (syn) taken from the motor. The secon- dary vibrations C n+1 for a sampling period n + 1 are determined as follows: C n+1 = C n -.mu.E n SGN(l/~], where C n represents the secondary vibrations produced during a preceding sampling period (n); E n represents the detected error signal for said preceding period n, H represents the transfer coefficient between the actuat or (2) and the detector (4) and .mu. is a scaling fac- tor where 0 < .mu. < 1. The apparatus is in one embodiment configured as an add-on unit for a personal computer (PC) including circuit board which fits into an expansion slot of the PC.
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