| 摘要 |
PURPOSE:To reduce a fan sound without impairing an exhausing performance of a fan by a method wherein a speaker emitting a sound in the same direction of a fan sound is disposed on an outside surface provided with the fan in proximity to the fan. CONSTITUTION:A fan sound 12, such as a motor sound, is produced in a fan 2. The fan sound 12 is picked up by a microphone 3 as a sound 2g together with a noise and converted to electric signals 3h. Fan sound signals 10 based on the fan sound 12 are extracted out of the electric signals 3h by a fan sound signal extraction circuit 4. Succeedingly, reverse-phase signals 11 having a phase reverse to the fan sound signal 10 are produced by a reverse-phase signal producing circuit 5. The reverse-phase signals 11 are converted to a masking sound 13 by a speaker 6. The masking sound 13 is emitted in the same direction of the fan sound 12. The masking sound 13 having a phase reverse to the fan sound 12 offsets the fan sound 12 so as to reduce the fan sound 12. |
