Active noise control systems for controlling outdoor environmental noise

A unique theory for generating electronically controlled acoustic shadows for environmental noise reduction was reported in [1]. The theory has been extended to complex high frequency sound from large non-compact sources [2] and implemented into hardware [3]. These studies show that deep acoustic shadows are possible. This paper considers the implementation of the theory into a practical multichannel freefield control system. Providing certain stability conditions are met, it is found that deep shadows >60dB are generated. For this to be accomplished, the detailed transfer functions of the adaptive system have to be known. Prediction and measurement techniques for these functions are given.