Active control of noise propagation outdoors.

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Most of the current research on active noise control is confined to restricted spaces such as earphones, active silencers, air-conditioning ducts, truck cabins and aircraft fuselages. In this study, thc basic concepts of road traffic noise reduction by using active noise control in unconfined spaces are explored. The approach is to develop a controlled acoustic shadow, gcnerated by a wall of secondary sources, to reduce unwanted sound in the direction of a complalnt area. The basic JMC theory is considered, followed by computer modelling, and experimental measurements. In the experiments, tripole secondary sound sorces were used to control the wall of secondary sources. Wide noisy area were controlled to a quiet space by our active noise control system. The application to the road traffic noise problem was discussed.