SPATIAL DELTA-SIGMA MODULATION FOR DIRECTIVITY CONTROL OF AN ACOUSTIC PIXEL ARRAY USING CNT

Abstract

Conventional sound field reproduction technique requires extensive multi-channel signal pro-cessing to control the beampattern of a speaker array. In this paper, we introduce a simplified di-rectivity control strategy, in which a designated beampattern is synthesized through the control of individual polarity of very small speaker units. Each small speaker operates like a pixel of a display panel, and the combination of multiple pixels using a spatial binary pattern produces the designated beampattern. A Spatial Delta-Sigma Modulation (DSM) technique is used to convert the continuous spatial excitation pattern into a binary pattern. For the speaker unit, thermoacoustic speakers made up of vertically aligned carbon nanotubes (VACNT) is selected for its sound radiation characteristic less influenced by radiating area. The experiment with a prototype pixel display shows that the di-rectivity control is possible with negligible errors.