Free field rooms for industrial applications

Abstract

In order to develop a cost-effective design for a free field room having an overall shape of a rectangular parallele piped, we predict the acoustical field within such rooms by summing the contributions of the six primary images formed by the four walls, the ceiling, and the acoustically “hard” floor. Although the reflected energy in rooms of this type can be significant near the room boundaries, there generally exists a region around the source where sound pressure level measurements can be made that will be the same as those obtained with the source out-of-doors and resting on an acoustically hard surface. The performance of a free field room is, therefore, described in terms of the sound pressure levels that would exist out-of-doors. Because the constructive and destructive interference between the source and the image formed by the ground plane obscures the conformity of the sound field with the inverse square law, we have used a carousel method for evaluating the performance of free field rooms having “hard” floors.