Recently, scientists have solved one ancient mystery that has been bothering mankind since before the Common Era. Why does the theatre at Epidaurus in Greece have such great acoustics? The acoustics of the theatre have been described as "perfect," which is not bad, considering the ancient Greeks thought that bugs came from meat.
The theatre at Epidaurus can hold audiences of up to 14,000. The theatre contains 55 semi-circular rows, and as far as sound goes, every seat is a good seat. Even in the nosebleeds, audiences can hear actors un-amplified. You can literally hear a pin drop!
The theatre is located near the ancient sanctuary of Asklepio. The sanctuary, which is dedicated to Asklepios, the god of healing, was used as a therapeutic and religious center for the ancient Greeks. The sanctuary itself is home to many interesting buildings, but none more fascinating or mysterious as the theatre.
The theatre was built in the 4th century B.C. It was constructed by Polykleitos the Younger. It's also one of the best preserved theatres of Ancient Greece, so there's a lot to learn from the structure.
When studying the structure, researcher Nico Declercq jumped to conclusions. He thought that the slope of the theatre was responsible for the acoustics of the theatre. You would think that, but also if you thought that you'd be wrong.
Declercq explains his reasoning. "When I first tackled this problem, I thought that the effect of the splendid acoustics was due to surface waves climbing the theater with almost no damping," said Declercq. "While the voices of the performers were being carried, I didn't anticipate that the low frequencies of speech were also filtered out to some extent."
But after some experiments with ultrasonic waves and numerical models, the slope theory was ruled out. Per Declercq, the experiments showed that frequencies up to 500 hertz (cycles per second) were lowered, and frequencies higher than 500 hertz went undiminished. There goes that idea!
The seats of the theatre at Epidaurus are built out of limestone. According to researchers from the Georgia Institute of Technology, this material creates a "filtering effect." Low frequencies of voices are suppressed, which means that background crowd noise is minimized. Which also means that you don't have to keep on turning around to tell the person behind you to shut up.
But the awesome power of limestone doesn't stop there. The limestone also reflects high frequencies back towards the audience. So it doesn't matter where you sit, you're going to have a good seat. Unless, of course, you're sitting down wind of someone with gas.
Essentially, the theatre is designed to shut out the sound you don't want coming in. "Most of the noise produced in and around the theatre was probably low-frequency noise," said Declercq. "The cut-off frequency is right where you would want it if you wanted to remove noise coming from sources that were there in ancient times."
But the theatre's acoustics can't be 100 percent credited to limestone. The human brain plays a part as well. "There is a neurological phenomenon called virtual pitch that enables the human brain to reconstruct a sound source even in the absence of the lower tones," Declercq says. "This effect causes small loudspeakers to produce apparently better sound quality than you'd expect."
The thing that is more astounding about the acoustics at the theatre of Epidaurus is that even the ancient Greeks didn't know why it sounded so good. Attempts to recreate the theatre using other materials for the seats, like wood, have failed. Now we know why.