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Digital Object Identifier 10.1109/MSP.2014.2360707

Date of publication: 12 February 2015

ound rendering is increasingly being required to extend

over certain regions of space for multiple listeners,

known as personal sound zones, with minimum interfer-

ence to listeners in other regions. In this article, we pres-

ent a systematic overview of the major challenges that

have to be dealt with for multizone sound control in a room. Sound

control over multiple zones is formulated as an optimization prob-

lem, and a unified framework is presented to compare two state-of-

the-art sound control techniques. While conventional techniques

have been focusing on point-to-point audio processing, we introduce

a wave-domain sound field representation and active room compen-

sation for sound pressure control over a region of space. The design

of directional loudspeakers is presented and the advantages of using

arrays of directional sources are illustrated for sound reproduction,

such as better control of sound fields over wide areas and reduced

total number of loudspeaker units, thus making it particularly suit-

able for establishing personal sound zones.

INTRODUCTION

Sound recording and sound reproduction are becoming increas-

ingly ubiquitous in our daily lives. The ultimate goal of sound

reproduction is to recreate the full richness of a sound field

including not only the sound content but also the spatial proper-

ties to give the listener full knowledge about both the sound

source and acoustic environment. Spatial sound reproduction

technologies so far have made tremendous progress in reproduc-

ing sound fields over fairly large regions of space using an array of

loudspeakers. This introduces the idea of establishing personal

sound zones, whereby interface-free audio is delivered to multiple

listeners in the same environment without physical isolation or

the use of headphones (Figure 1). This concept has recently drawn

attention due to a whole range of audio applications, from control-

ling sound radiation from a personal audio device to creating indi-

vidual sound zones in all kinds of enclosures (such as shared

offices, passenger cars, and exhibition centers) and generating

quiet zones in noisy environments.

The first known demonstration of reproducing a sound field

within a given region of space was conducted by Camras at the

Illinois Institute of Technology in 1967, where loudspeakers

were distributed on the surface enclosing the selected region to

control sound radiation, and the listeners could move freely

within the recreated environment [1]. The well-known ambi-

sonics [2], wave field synthesis [3], and higher-order spherical

harmonics-based techniques [4] were developed separately for

more advanced spatial sound field reproduction over a large

region of space. Druyvesteyn and Garas [5] first proposed the

[

Delivering interface-free audio to multiple listeners

]

EARPHONES—IMAGE LICENSED BY INGRAM PUBLISHING

[

Terence Betlehem, Wen Zhang, Mark A. Poletti, and Thushara D. Abhayapala

]

Personal Sound Zones

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