Quiet Zones for Active Control of Sound Using Spherical Loudspeaker Array

Active control of sound can be employed globally to reduce noise levels in an entire enclosure, or locally around a listener‘s head. Recently, spherical loudspeaker arrays have been studied as multiple-channel sound sources capable of generating sound fields with high complexity. In this paper, several aspects of using a spherical loudspeaker array for local active control of sound are investigated. The first topic under investigation in this paper is the feasibility of creating sphere-shaped quiet zones away from the source. These can be useful in practice to cover the space around a listener‘s head. However, zones of quiet created away from the source tend to force the secondary source to produce zones of amplification away from the quiet zone. It is shown that by designing quiet zones in the form of a shell around the source, sound amplification can be significantly reduced. Finally, the combination of several spherical sources to enlarge the quiet zone will be demonstrated.