The theater at Epidaurus in the fourth century B.C. creates a sophisticated acoustic filter. Without any sound systems, audiences in the back row are able to hear music and voices with amazing clarity. The rows of limestone seats at Epidaurus form an efficient acoustics filter that hushes low-frequency background noises like the murmur of a crowd and reflects the high-frequency noises of the performers on stage off the seats and back toward the seated audience member, carrying an actor’s voice all the way to the back rows of the theater. The corrugated surface of the seats was creating an effect similar to the ridged acoustics padding on walls or insulation in a parking garage.