Evaluation of noise reduction performance of active noise control with optical laser microphone in reverberant environments

A feedforward active noise control system has a constraint on the processing and sound propagation delay. It is called the causality constraint. The feedforward active noise control system with an optical laser microphone has been proposed to relax the causality constraint. The optical laser microphone acquires the vibration velocity of the target noise with the speed of light. Therefore, the causality constraint is relaxed. However, the acquired signal contains little the reverberation characteristics of the room. Therefore, the noise reduction performance of the system is degraded in reverberant environment. Hence, this paper proposes a multichannel feedforward active noise control system for noise reduction in reverberant environments. The proposed system has the optical laser microphone and an air-conducted microphone as reference microphones. The unique point of this system is the additional air-conducted microphone, which acquires the reverberation components. The proposed system processes signals acquired by each microphone with separate noise control filters. This simultaneously relaxes the causality constraint and takes into account the reflection characteristics of the room. In this paper, the noise reduction performance of the proposed system is evaluated by the real-world experiments.