A fan noise canceller comprises a rotation information detecting means 2 (or 12) for detecting noise information of a fan 1 (11), a band-pass filter 3 (13) for extracting the blade passing frequency from the noise information, an output control means 4 (14) for controlling the amplitude and phase of...http://www.google.fr/patents/US6188770?utm_source=gb-gplus-shareBrevet US6188770 - Fan noise canceller
