A silencer is to be used in combination with a range hood system to suppress noise made by a fan. In a silencing circuit, a disturbance detector detects mixing of disturbance sound to a correction signal and an error signal. When the disturbance detector detects the mixing of the disturbance sound, an updating stopper causes a coefficient updater to stop a processing of updating a filter coefficient of a silencer filter, relating to, as an object, at least a frequency band other than a frequency band of the noise.

A cooker hood with function of active noise cancellation is disclosed. The cooker hood comprises a hood body, a chimney, a fan motor, a sound-absorbing member, and an ANC system, in which the sound-absorbing member blocks or destroys a sound wave of a noise sound produced in case of the operation of the fan motor. The ANC system comprises reference microphones, error microphones, an electronic device, and loudspeakers, and is utilized for collecting a noise sound in chimney, generating an anti-noise signal according to the noise sound, and driving the loudspeaker to broadcast an anti-noise sound toward an internal of the chimney. Briefly speaking, the sound-absorbing member and the ANC system are used to apply a passive noise cancellation treatment and an active noise cancellation treatment to the noise sound produced during the operation of the fan motor.

The present invention is in the field of an active sound-cancellation system, an open fluid-duct comprising such an active sound-cancellation system, such as an air duct, and an active sound-cancellation computer program comprising instructions for operating such an active sound-cancellation system. The active sound-cancellation system reduces noise significantly.