Epidaurus' ancient seats are a built-in acoustic filter

The Theatre of Epidaurus, built in the 4th century BCE, seats up to 14,000 people across steeply raked tiers of limestone — and visitors have long marvelled that words spoken on the stage reach the highest seats.

In 2007, Georgia Tech researchers Nico Declercq and Cindy Dekeyser proposed why. The corrugated rows of limestone seats act as an acoustic filter: they damp low-frequency sounds below about 500 Hz — the murmur of the crowd and wind — while reflecting the higher frequencies of a performer’s voice back toward the audience. The brain then reconstructs the missing low tones, so speech still sounds full.

The popular claim that you can hear a whisper or a dropped coin from the back row is overstated, though. A 2017 acoustic study of three Greek theatres found a whisper carried only to the front rows, and that the ancient surfaces and actors’ masks likely mattered too.