Spatial manipulation and implementation of sound

Abstract

In this study, we aim to control the sound field spatially, so that a desired or target acoustic variable is enhanced within a zone where the listener is located. This is somewhat analogous to have manipulators that can draw sound in any place we want. In order to manipulate sound over a finite area in space, it is essential to control multiple sound sources. With all these regards, we propose a unified approach that can enhance selected acoustic variables using multiple sources. However, the shape or color of drawn sound field fully depends on the acoustic quantity we want to enhance. Among the many possible choices, this study focuses on three acoustic variables that have to do with the magnitude and the direction of sound. The first one is connected to the spatial control of acoustic potential energy. The enhancement of acoustic potential energy enables us to make a zone of loud sound over a selected area. This problem is defined as an acoustic brightness problem. We can also make a zone of loud sound and a quiet zone at the same time. This kind of control can be realized by maximizing acoustic brightness ratio, i.e., acoustic contrast of two different zones. The second acoustic quantity of concern is a perceived direction of sound source. It is shown that we can control the direction of perceived sound source by focusing acoustic energy on a desired wavenumber. It is noteworthy that we can also enhance the magnitude and direction of sound at the same time by controlling sound intensity. Through the manipulation of sound intensity, the direction of power flow can be controlled in a desired direction within a zone of interest. To begin with, pure-tone sound field is studied. In order to control acoustic potential energy in space, the concepts of acoustic brightness and contrast are defined and formulated. The optimal control signals of the multiple sources are obtained by simple eigenvalue analysis. Then the acoustic contrast control is applied ...