Personal audio and the active control of sound in the environment

As well as being able to reproduce sound in one region of space, it would be useful in many applications to be able to control the level of reproduced sound in other spatial regions. This is motivated by issues of privacy for the user and the need to reduce annoyance for other people nearby. The techniques for implementing this kind of “personal audio” using array of loudspeakers have much in common with systems for the active control of sound, where the traditional objective has been only to reduce the sound level in environments such as cars and aircraft, for example. Several practical examples of personal audio systems will be described, including using an array of loudspeakers in headrests to reproduce separate audio channels in adjacent seats, a system to reduce radiated sound from hands-free mobile devices and zonal amplification of TV audio. These systems often have a fundamental trade-off between performance and array effort, where the latter affects both the electrical power requirements of the array and its robustness to variations in driver response. Signal processing strategies will be described that allow a good compromise to be drawn between these competing requirements.