| 摘要 |
PURPOSE:To eliminate the whole frequency range of a noise by emitting an opposite phase sound wave conforming to the noise wave in a direction corresponding to noise wave surface of a duct. CONSTITUTION:An aperture area formed by slits 8a and 9a changes according to the waveform of a current applied through a coil 11, and air flow changes. As a result, the sound pressure of the whole surface of the slit 9a changes according to the waveform of a current. That is, by inputting outputs from a noise detecting means consisting of a microphone 4, etc., a delay circuit 6 and a phase inverter 7 to a coil 11, the waveform to be the sound at the same frequencies as those of the current is emitted in a duct 2 in the direction corresponding to the wave front of the noise. Thus, the whole frequency range of the noise generated in the duct can be eliminated. |
