Sound Focusing Based on Optimal Loudspeaker Array Beamforming

Sound focusing is an important problem in audio reproduction, where a virtual acoustic source needs be synthesized in the region surrounded by a loudspeaker array. This problem was tackled in the previous research via the Helmholtz integral approach, brightness control, acoustic contrast control, etc. In this paper, the same problem was revisited from the perspective of beamforming. A source array model is reformulated in terms of the steering matrix between the source and the field points, which lends itself to the use of beamforming algorithms such as minimum variance distortionless response (MVDR) and linearly constrained minimum variance (LCMV) originally intended for sensor arrays. The beamforming methods are compared with the conventional methods in terms of beam pattern, directional index, and control effort. Objective tests are conducted to assess the audio quality by using perceptual evaluation of speech quality (PEAQ). Experiments of produced sound field and listening tests are conducted in a listening room, with results processed using Analysis of Variance (ANOVA), post hoc Fisher’s least significant difference (LSD) test, and regression analysis. In contrast to the conventional energy-based methods, a key advantage of the proposed methods is their phase-sensitive characteristic in light of the distortionless constraint in formulating the array filters. The results demonstrate that minimized distortion helps enhance audio quality and focusing performance.