Why whispers at Epidaurus travel clearly to fourteen thousand spectators.
ADesigned in the fourth century BCE, the stone amphitheatre of Epidaurus allows an unamplified actor's sigh to be heard distinctly sixty metres away in the topmost tier. Popular myths attributed this clarity to prevailing hillside breezes or hidden bronze resonators.
BIn 2007, acoustic physicists measured sound reflection off the steep limestone seating rows and discovered that the corrugated step spacing acts as a natural high-pass acoustic filter. Low-frequency background murmur from wind and rustling garments below 500 hertz is scattered away, while higher vocal consonants propagate cleanly upward.
Epidaurus achieves clear speech transmission mainly by filtering out frequencies below 500 hertz.