4pNS7. Sound diffraction effects by screens in a room.

Session: Thursday Afternoon, December 5

Time: 3:45

Author: Dominique M. Habault
Location: CNRS, Lab. de Mecanique et Acoustique, F-13402 Marseille Cedex 20, France
Author: Ulf R. Kristiansen
Location: N. T. N. U., Acoust. Group, N-7034 Trondheim, Norway


Several numerical methods are used to describe the effects of diffraction by two kinds of screens in a room: a perfectly rigid screen and a vibrating screen. This study has two main applications in acoustics: In room acoustics, the aim is to describe the influence of a vibrating screen on the acoustical characteristics of a room in which screens made of light materials are suspended from the ceiling; in structural acoustics, it is to describe the effect of a vibrating structure in a cavity. An application in active noise control is also presented. First, the sound pressure in the room is computed by using a boundary element method. Then, a perturbation method is used in the case of the vibrating screen. Comparisons are made between the two methods and a finite-element method for two typical geometries. The numerical examples presented correspond to a 2-D problem and a rectangular room. From the acoustics point of view, it is shown that the effect of a vibrating screen compared with a rigid screen is bigger at low frequencies and for light materials. This difference also depends on the acoustical properties of the room (i.e., the reflection coefficients on the walls).

ASA 132nd meeting - Hawaii, December 1996