IWAI KENTA

In this paper, we propose a multichannel active noise control (ANC) system with an optimal reference microphone selector based on the time difference of arrival (TDOA). A multichannel feedforward ANC system using upstream reference signals can reduce various noises such as broadband noise by arranging reference microphones close to noise sources. However, the noise reduction performance of an ANC system degrades when the noise environment changes, such as the arrival direction. This is because some reference microphones do not satisfy the causality constraint that the unwanted noise propagates to the control point faster than the anti-noise used to cancel the unwanted noise. To solve this problem, we propose a multichannel ANC system with an optimal reference microphone selector. This selector chooses the reference microphones that satisfy the causality constraint based on the TDOA. Some experimental results demonstrate that the proposed system can choose the optimal reference microphones and effectively reduce unwanted acoustic noise.

In this paper, we propose a modified second-order nonlinear infinite impulse response (IIR) filter for equalizing the frequency response and compensating nonlinear distortions of an electrodynamic loudspeaker. A problem of electrodynamic loudspeakers is the generation of nonlinear distortions, which degrade the sound quality. One of the approaches to reducing nonlinear distortions is to use a second-order nonlinear IIR filter. This filter is based on an equivalent circuit model of an electrodynamic loudspeaker and its coefficients are determined by physical parameters. However, it is difficult to compensate nonlinear distortions when a loudspeaker has a high Q factor at the lowest resonance frequency, at which the displacement of the diaphragm and nonlinear distortions become large. The Q factor determines the linear frequency response of the electrodynamic loudspeaker. Although it is necessary to compensate the Q factor of the loudspeaker, a nonlinear IIR filter cannot compensate the Q factor because it does not have a linear filtering feature. In this paper, we propose a modified second-order nonlinear IIR filter that can not only compensate the nonlinear distortions caused by the nonlinearities of the force factor and stiffness but also equalize the frequency response by employing the linear characteristics of the loudspeaker with the desired Q factor. Experimental results show that the proposed filter can compensate the linear and nonlinear distortions more effectively than a conventional filter.

In this paper, we propose a modified 2nd-order nonlinear IIR filter for compensation of both linear and nonlinear distortions of electrodynamic loudspeakers. A nonlinear IIR filter is a nonlinear compensator and is based on a physical nonlinear model of electrodynamic loudspeakers. However, it is difficult to compensate nonlinear distortions when a loudspeaker has large sharpness at the lowest resonance frequency, at which the displacement of the diaphragm becomes large. Although it is necessary to compensate the sharpness of the loudspeaker, the nonlinear IIR filter cannot compensate the sharpness because it does not have a linear filtering feature. In this paper, we propose a modified 2nd-order nonlinear IIR filter that can compensate not only the nonlinear distortions but also the sharpness by employing the linear characteristics of the loudspeaker with the desired sharpness. Experimental results show that the proposed filter can compensate the linear and nonlinear distortions more effectively than a conventional filter.