| 摘要 |
PURPOSE:To enhance an attenuation capacity by controlling a filter means so as to extract a frequency band to be muffled in conformity with a noise level and frequency after attenuation in a device which detects a noise in a duct and generates sound waves on a reverse phase and attenuates the noise. CONSTITUTION:A microphone 3 is installed so as to detect a noise 3 in a duct 1. An electric signal is input from this detection microphone 3 into a bandwidth pass filter 6. The electric signal in the frequency band of a specified band-width component is input into a controller 12 by way of a fan 7a and an A/D converter 8a, where there is generated sound data (damping component signal), which is identical in the amplitude on a reverse phase per each frequency, based on an input signal. The damping component signal is output to a power amplifier 10 by way of a D/A converter 11 and a low pass filter 13 and damps the noise by rumbling a speaker 5. In addition, a monitor microphone 4 is used to detect the sound after it is dumped and controls shutoff frequency of the bandwidth pass filter 6 and 8 based on the data. |
