The general effect of the walls of the Auditorium on the sound may be anticipated by considering analogous cases in geometrical optics, but with the restrictions on “rays” described in the preceding paragraph. The sound does not actually confine itself to the sharp boundaries shown. The diagrams are intended to indicate the main effect of the sound in the region so bounded. [Fig. 7] gives such an idea for the concentration of sound in the longitudinal section of the Auditorium.
The plan followed in the experimental work was to anticipate the path of the sound as indicated in [Fig. 7], then to verify the results with the arc-light reflector. [Figs. 8] and [9] show the effect of the rear wall in the balcony in forming echoes on the stage. The speaker was particularly unfortunate, being afflicted with no less than ten echoes.
Fig. 8. Longitudinal Section Showing how Sound Is Returned to the Stage to Form an Echo.
Fig. 9. Longitudinal Section Showing Formation of Echo on the Stage.
The hard, smooth, circular wall bounding the main floor under the balcony gave echoes as shown in [Fig. 10], the sound going also in the reverse direction of the arrows.
Fig. 10. Plan of Auditorium Showing Action of Rear Wall on the Sound.
