Scattered Responses From Suspended Reflector PanelsWith Rounded Edges

Sound reflections from most finite surfaces, such as overhead reflector panels, include a component known as edge diffraction. Edge diffraction is the scattered energy required to maintain a continuous sound field despite the discontinuity in acoustical impedance presented by the scatterer. Edge diffraction can interfere with primary scattered energy to produce comb filtering at receiver locations. Several decades ago, the effect of changing the edge profile of loudspeaker boxes was investigated with the goal of producing a smoother frequency response. By rounding the edges of loudspeaker boxes, the edge diffraction could be decreased noticeably [H. F. Olson, J. Aud. Eng. Soc. 17 (1), 22-29 (1969)]. In the current study, boundary element methods are used to study the results of rounding the edges of suspended reflector panels with the same intent of diminishing the boundary wave to achieve a smoother response across the audience area. Specific attention is given to the spatial range and frequency range over which this effect can be achieved. INTRODUCTION AND BACKGROUND This paper investigates the simulated responses of reflector panels with convex edges. The convex edges are designed to smooth the scattered response from the reflector panel. The background for this investigation comes from investigations of direct radiator loudspeakers. The diffracted wave from direct radiator loudspeakers The effect of sound diffracted from the edge of a finite baffle has been well documented. When a source is placed in a finite baffle, secondary sources appear at the edge of the baffle where the sound wave is diffracted. The interference between the direct energy and the energy diffracted from the edge creates fluctuations in the total sound field, as shown in Figure 1 (after Beranek [1]). The frequencies at which interferences occur can be calculated based on travel time from the source in the middle of the baffle and from the edge. Figure 1.Diffracted wave from the edge of a baffle (after Beranek [1]). A comprehensive measurement study was undertaken by Olson [2] in which the shape of direct radiator loudspeaker enclosures was varied with the goal of reducing the strength of the diffracted wave. With a diminished diffracted wave, or boundary wave, the response from the radiator is much smoother because it is not subject to the interferences between the direct and diffracted energy. Olson found that a spherical loudspeaker enclosure produced no boundary wave due to the absence of sharp edges or discontinuities.