Active noise control of an incoherent line source

In this paper the outdoor active noise control of the sound pressure created by an incoherent line source is studied. Such a source is a model for the noise generated by road traffic or by trains and consists of a continuous distribution of uncorrelated point sources. By using this model, the possibility of generating quiet zones for environmental noise is examined. For this purpose the statistical properties of the sound pressure are first studied. Then the efficiency of active control by point sources is calculated as a function of both frequency and position and comparisons are made between finite and infinite length primary sources. Finally, the investigation is extended to the calculation of the pressure crossing an aperture in a rigid plant: to simulate the energy entering into a room through an open window. The energy crossing the aperture is calculated with and without control to determine the noise reduction potentially provided by the active control. (C) 1998 Academic Press Limited.