| 摘要 |
PURPOSE:To reduce the noise of a rotary body by the interference with the sound of which the phase is reverse to that of the noise of a rotary body such as a fan and having the same sound pressure as the noise emitted from a newly provided speaker. CONSTITUTION:The number of rotations of a cooling fan 2 is measured by a number-of-rotation detection circuit 55 to be inputted to a digital/analogue processor 50 (hereinbelow referred to as DSP) to operate the noise frequency of the fan in the DSP 50. This frequency is set to a reference signal and a signal reverse to fan noise in phase and having the same amplitude as the fan noise is formed by the digital filter and delay circuit in the DSP 50 and a control speaker 3 is sounded through a D/A converter 51 and a power amplifier 52. Next, the reduction effect of noise due to mutual interference is measured by an evaluation microphone 4 to be inputted to the DSP 50 through a microphone amplifier 54 and an A/D converter 53 and, by adapting the digital filter in the DSP 50 so as to reduce the noise from a microphone 4, the noise 2 of the fan 2 can be reduced. |
