矩形波によるヘテロダインを利用した能動的音響制御における騒音周波数の変化への追従性の検討

抄録

In general, active noise control is not effective to attenuate high frequency noise. In this paper, the active noise control using heterodyne is proposed in order to realize the active noise control of high frequency noise with lower cost. Heterodyne is a signal processing technique that creates new frequency components by multiplying signals of two frequencies. By using this technique, if the frequencies of the input signal and the heterodyne wave are 𝜔 and 𝜔_", the frequencies of the output signals become summation and difference of 𝜔 and 𝜔_". Then, through appropriate filtering process, either one signal can be obtained. In this paper, frequency shift of 2000 Hz by using heterodyne with the square wave is considered to attenuate 2200-2400 Hz noise with the controller whose sampling frequency is 2000 Hz. Numerical analysis is conducted with two algorithms, Filtered-X LMS algorithm and Virtual Error Method. The former needs to identify acoustic characteristic before control and the later identifies acoustic characteristic during control. Two types of noise are demonstrated to be attenuated. One is the white noise and the other is the chirp noise. The frequency of each noise was 2200-2400 Hz . The white noise was largely attenuated with each algorithm (about 20 dB) and the chirp noise was also attenuated with Filtered-X LMS algorithm (about 15 dB). On the other hand, some problems were found with Virtual Error Method. Several peaks were detected in the error signal during control.