| 摘要 |
<p>Primary vibrations (N), e.g. acoustic noise or vibration from a source thereof such as a motor, are cancelled by secondary vibrations (C) produced by an actuator (2) driven by a controller (3) that is 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 error signal (E) during successive sampling periods determined by a synchronising signal (syn) taken from the motor. The secondary vibrations Cn+1 for a sampling period n+1 are determined as follows: Cn+1 = Cn-νEnSGN[1/H^¨B7], where Cn represents the secondary vibrations produced during a preceding sampling period (n); En represents the detected error signal for said preceding period n, H represents the transfer coefficient between the actuator (2) and the detector (4) and ν is a scaling factor where 0« ν « 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.</p> |
