ABSTRACT
In this chapter, the second of the general classes of active noise control problems, the active control of sound radiation into free space, will be examined. As with the previous chapter on controlling sound propagation in ducts, principal consideration will be given to the ‘physical’ part of the active noise control system; models will be derived that enable prediction of the effects of applying active noise control, both to the acoustic field and to the acoustic radiation characteristics of the noise sources. These models can then be used in analysis of the physical mechanisms of active control, and in system design exercises, where the aim is to find an arrangement of sources and sensors that is capable of providing the maximum level of disturbance attenuation. In practice, this arrangement would be driven by the feedforward control systems described in Chapter 6, or the feedback arrangements described in Chapter 5.
