Time-frequency diffraction acoustic modeling of the Epidaurus ancient theatre

Abstract

This work provides an in-depth investigation on the effect of sound diffraction in the acoustics of the ancient theatres, with reference to the theatre of Epidaurus. It is increasingly evident that in such theaters, sound diffraction at the edges of the multiple tiers generates significant source signal amplification. Especially for the distant listener positions, an accumulation (“avalanche”) effect from lower tier diffracted energy is identified. This study examines a 3D model of an elementary slice of the seating benches (“koilon”), evaluating the generated sound field in the time, frequency, and spatial domains. The analysis accounts for direct, reflected, diffracted and mixed reflected – diffracted paths and the theatre’s acoustic response is numerically evaluated in various positions along the koilon slice, accurately matching to in-situ measurements. The contribution of the diffracted sound to the total sound field is identified through a detailed and novel analysis of energy-based acoustic parameters, via the time and frequency responses as well as of the spatial parameters relating to listener-perceived effects. In all cases, the contribution of sound diffraction components is examined via its contribution to speech intelligibility from signals generated in the theatre’s orchestra and from a virtual reconstruction of the stage-scenic building.