Acoustics of Greek theatres

The best of the classical Greek theatres have remarkable acoustics for speech intelligibility, solo or unison singing, chanting, and for solo musical instruments. The essential property of the theatre structure to achieve this condition appears to be the architectural features that produce a profusion of “early reflected sound,” that is, sound reaching the listeners within 50 milliseconds of the direct sound, scattered by both seats and people. To a lesser degree, sound reflected from the orchestra and stage house appears to be important when these (as in the original Greek structures but not in the later Roman theatres) provide a spectrum of early reflected sounds with time delays of 20 millisec or less following the direct sound. The almost complete absence of reverberation and a wide spread of time delays (50 milliseconds or more) in the reflected and scattered sound make Greek theatres unattractive for orchestral music. But for their principal purpose of play production they were excellent, and when we consider that they employed no sound amplification but only strenuous effort by the performers, they are truly remarkable acoustical achievements.