Active control of sound waves

摘要

A sound wave propagated along a duct through a fluid contained in the duct is attenuated by generating sound waves from an array of sound sources spaced along the duct. Each source generates two waves travelling in opposite directions; those travelling in the same direction as the unwanted wave sum to give a resultant which interferes destructively with the unwanted wave, while those travelling in the opposite direction sum to give a negligible resultant. The source array may be operated in response to detection of the unwanted wave.