The ERATO project (2003-2006, Contract Number ICA3-CT-2002-10031), was a three-year research project financed by the European Commission under the Fifth Framework INCO – MED Program. The ancient Greek and Roman theatres are famous for the excellent acoustics. However, it is not generally well known that different kinds of theatres were built, for different purposes and with different acoustical conditions. One of the aims in the ERATO project has been to investigate the acoustics of the open air theatre and compare to the smaller, originally roofed theatre, also called odeum (from Greek: Odeion, a hall for song and declamation with music).

The method has been to make computer models of the spaces, first as they exist today, and adjust the acoustical data for surface materials by comparison to acoustical measurements from some of the best preserved examples, namely the Aspendos theatre in Turkey and the South theatre in Jerash, Jordan. Next step was to complete the computer models in accordance with archaeological information, to make virtual reconstructions of the spaces. The acoustical simulations have given a lot of interesting information about the acoustical qualities, mainly in the Roman theatres, but the earlier Greek theatre has also been studied in one case (Syracusa in Italy). It is found that the Roman open-air theatres had very high clarity of sound, but the sound strength was quite low. In contrast, the odea had reverberation time like a concert hall, relatively low clarity, and high sound strength. Thus, the acoustical properties reflect the original different purposes of the buildings, the theatre intended mainly for plays (speech) and the odeum mainly for song and music.