Control robustness of freefield active noise control systems

A unique theory for generating electronically controlled acoustic shadows for environmental noise reduction was reported by Write and Vuksanovic (1996). The theory has been extended to complex high frequency sound from large noncompact sources. These studies show that deep acoustic shadows are theoretically possible. This paper considers the implementation of the theory into a practical multichannel freefield control system and its performance. Providing certain stability conditions are met, it is found that deep shadows >60 dB are generated at the microphones, limited only by the ambient noise of the laboratory. This sets the stage for practical systems to be built