Project Ancient Acoustics Part 2 of 4 : large-scale acoustical measurements in the Odeon of Herodes Atticus and the theatres of Epidaurus and Argos

In the last decades we have seen an increased interest in the acoustics of ancient Greek and Roman theatres and much research has been performed on many of them. Research has mainly focused on modelling the acoustics of theatres and has shown various acoustical effects. However, only a limited number of in situ measurements have been available to validate the results. In this paper, results are presented of large-scale measurements which were performed in the Odeon of Herodes Atticus and the theatres of Epidaurus and Argos. The accuracy of these measurements is discussed in part one of this series of papers. Impulse response measurements have been conducted at respectively 200, 264 and 60 listener positions for 5 equal-angular dodecahedron sound source rotation steps at 2 source positions. In addition, binaural impulse responses were measured using an artificial head on respectively 10, 12 and 3 receiver positions. Finally, speech intelligibility measurements have been carried out in accordance with IEC 60268-16 using a ‘speech source’ that simulates a human voice. In the Odeon of Herodes Atticus, all measurements have been performed in the morning as well as in the evening, showing a minimal discrepancy well within the Just Noticeable Difference (JND) for every discussed parameter. This proves that it is legitimate to compare measurements collected during a full day under slightly different climate conditions. Results for the Odeon of Herodes Atticus show a uniform axisymmetric distribution over receiver positions of common acoustical parameters such as reverberation time, clarity, sound strength and spaciousness. For the theatre of Epidaurus this distribution is non-uniform dueto the opposite-facing seating areas, which is in line with findings from research by others. The results of the speech intelligibility measurements show a declining trend for STI over distance, which contradicts some findings presented in literature