Theory and Design of Feasible Active Noise Control Systems for 3D Regions

Abstract

This thesis advances Active Noise Control (ANC) over three-dimensional (3D) space using feasible loudspeaker and microphone array systems. By definition, ANC reduces unwanted acoustic noise by generating an anti-noise signal(s) from secondary loudspeakers. The concept of spatial ANC aims to reduce unwanted acoustic noise over a continuous 3D region, by utilizing multiple microphones and multiple secondary loudspeakers to create a large-sized quiet zone for listeners in three-dimensional space. However, existing spatial ANC techniques are usually impractical and difficult to implement due to their strict hardware requirements and high computation complexity. Therefore, this thesis explores various aspects of spatial ANC, seeking algorithms and techniques to promote the reliability and feasibility of ANC over space in real-life applications. The spherical harmonic analysis technique is introduced as the basis of conventional spatial ANC systems. This technique provides an accurate representation of a given spatial sound field using higher-order microphone (spherical microphone array) recordings. Hence, the residual noise field in a spatial ANC system can be effectively captured spatially by applying the spherical harmonic technique. Incorporating conventional spatial ANC methods, we developed a series of algorithms and methods that optimize conventional methods regarding array geometries and ANC algorithms, towards improving the feasibility of a conventional spatial ANC system involving the spherical harmonic analysis. Overall, motivated by feasible and realistic designs for spatial ANC systems, work included in this thesis mainly solves the three problems of: (i) the impracticality of realizing spherical microphone and loudspeaker arrays, (ii) achieving secondary channel estimation with microphones remote from their desired locations, and (iii) unreasonable delays inherent to frequency domain spatial ANC methods. Based on our work, we have stepped towards achieving a spatial ANC system in a real-world environment for people to enjoy silence in the control region with the reliable usage of resources and algorithms. Several contributions of this work are: (i) designing a 3D spatial ANC system using multiple circular microphone and loudspeaker arrays instead of spherical arrays, (ii) proposing a 3D spatial ANC method with remote microphone technique such that noise reduction over a region is achieved with microphones remote from the region, (iii) proposing a secondary channel estimation method using a moving higher-order microphone such that usage of an error microphone array is not necessary, (iv) deriving a time domain spherical harmonic analysis method for open spherical microphone array recording with less delay than in the frequency domain, and (v) designing a feed-forward adaptive spatial ANC algorithm incorporating the time domain spherical harmonic analysis technique to better minimize the noise in the region of interest. Show more