Sound-focusing effects in the plan of horse-shoe shaped opera theatres

An acoustical feature reported specifically for Italian-style opera houses is the non uniformity of early sound in the stalls. The curvature of the lower part of the lateral walls produces a sort of partial wave-guiding effect, like the well known "whispering gallery" effect. It is responsible of the concentration of early sound energy at seats located back in the stalls when the sound source radiates from the foreground of the stage floor. As much of the global room impression depends on the early part of the impulse response it can be supposed that the perceived sound quality of singers' voice and instrumentalists' music performed on the stage will be much different if the listener seats in the last rows with respect to different locations in the stalls. This paper reports an objective analysis on this subject based on measurements carried out in the stalls of "The Teatro di Corte della Reggia di Caserta". Relevant computer simulations were also implemented.