| 摘要 |
<p>PURPOSE:To securely mute a propagated sound wave, propagated in a duct, over a wide band. CONSTITUTION:In a duct 2 on the downstream side of a cavity type sound eliminator 12 coupled halfway to ducts 18 and 20, a speaker 22 which radiates an additional sound for canceling the propagated sound wave passed through the cavity type silencer 12 is provided and a microphone 24 which detects and converts an error after the additional sound from the speaker and the propagated sound wave interfere with each other into an electric signal is provided. A control part 28 is equipped with a period detection part 30 which detects the period of the periodic noise of the propagated sound wave or a dummy periodic noise on the basis of noise information from the microphone, an analog shift register 32 which has stages corresponding to tap length N and stores weighting coefficients in the respective stages, and outputs the stored weighting coefficients as a sequential driving signal by being driven so that one round is made at the period detected by the period detection part, and a weighting coefficient arithmetic part 36 which calculates a weighting coefficient for reducing the error signal on the basis of the driving signal outputted by the analog shift register and the error signal detected by the microphone and inputs the weighting coefficient to the analog shift register.</p> |
