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A local system for the active control of sound uses a secondary source to cancel the pressure at a closely spaced error microphone.This creates a zone of quiet around the cancellation point which becomes larger as the error microphone is moved further away from the secondary source.Since in a practical application the local active control may be implemented close to a listener's head, the physical presence of the head may affect the zone of quiet produced.The acoustic performance of such a local control system will be mainly determined by the geometric arrangement of the secondary source, error microphone and the head.This means that a suitable theoretical model has to take into account the diffraction effects on the secondary and primary fields due to the secondary source and the head.
BONITO et al. (Wed,) studied this question.