Fast Convergent Method for Active Noise Control Over Spatial Region with Causal Constraint

The aim of spatial active noise control (ANC) is to attenuate unwanted noise over a target region. Methods based on the spherical/circular harmonic expansion of the sound field have been proposed, enabling the control of a particular continuous area. These methods, however, are derived in the frequency domain; therefore, they cannot guarantee the causality of the control filters. On the other hand, time-domain adaptive methods have the problem of slow convergence. We propose a spatial ANC method that guarantees the control filter's causality and achieves fast convergence while controlling the continuous spatial area. The proposed method adopts the objective function of the recursive least squares algorithm and exploits the Markov conjugacy of search directions for fast convergence. Numerical simulations in a room environment indicated the efficacy of the proposed method compared with the conventional multipoint adaptive method.