Outdoor active noise control

A unique theory for generating electronically controlled acoustic shadows for environmental noise reduction was reported previously by the authors (1996). The theory (1997) has been extended to complex high frequency sound from large non-compact sources. These studies show that deep shadows >120 db are theoretically possible. The implementation of the theory into a multichannel free field control system and its operation has also been reported (1997). 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