Acoustical measurements in “Teatro Nuovo” (Spoleto, Italy), changing sound source position in performance area
Alessandro Cocchi, Ryota Shimokura and Marco Cesare

Like in other Italian opera houses, "Teatro Nuovo" in Spoleto (Italy) has horse-shoe shaped stalls and boxes in the balconies; however, the ceiling of the hall presents a strongly concave shape, and the orchestra pit is extraordinary large in consequence of the reconstruction. These geometrical characteristics influence the acoustical field for performance, and we have explored it with a measurement campaign moving the source positions in the performance areas (20 sound source positions either in the stage or in the pit). From the results, it comes out that the values of acoustical parameters calculated from 20 binaural impulse responses (BIRs) are too various to represent only one source position like usual measurements putting many receiver positions in the audience spaces. Moreover, in Teatro Nuovo, the concaved ceiling modifies the strength of reflections from it according to the source positions, and the large but low orchestra pit (floor; 12.15×12.84 m2 and height; 2.22 m) induces some resonance effects especially in the pit source positions covered by the forestage. The peculiar resonance can be visualized by introducing autocorrelation analysis of BIR after passing through the low-pass filtering (< 500 Hz). The acoustical parameters from the normalized ACF (Autocorrelation Function) of BIR would be useful to explain features of sound fields or to detect an acoustical difficulty like a flutter echo.

Keywords: acoustical measurement, Italian opera house and performance area