Roman theatres have always been the subject of research studies, under architectural perspective and archaeology other than acoustics. Many ancient theatres, like that one in Tyndaris, are well preserved, but others open-air theatres, like that one in Volterra, are partially preserved since the damages caused by natural events and human intervention heavily affected the original constructions. This paper deals with the acoustic analysis of the Roman theatre of Tyndaris, built in Sicily on the footprint of the original Greek construction, and the ancient theatre of Volterra, located in northern Italy and built during the 1st century BC. Nowadays, the theatre of Tyndaris, more preserved, is used for live artistical performance, while the theatre of Volterra is just open for museal visits. Two campaigns of acoustic measurements have been carried out in order to compare the results of a Roman theatre built on the footprints of the Greek construction with those related to an open-air theatre conservatively built by following the Vitruvian construction rules. The results have been assessed by taking into consideration that light music (classic quartets, not amplified) and prose are the main room functions, as it was in the past. The measured results indicate that the values related to the main acoustic parameters are typical of open-air ancient theatres, where the lack of architectural constructions like scenic building or summa cavea contribute to make the theatres drier for music performance, far from the original conditions.