0 Amphitheatre of Epidaurus acts as an acoustic filter

Epidaurus 

 Although the level of modern sound equipment, scientists believe that inventions by ancient architects acoustic filter can also be used in the construction of stadiums and outdoor theaters.
Physicists are on pace to explain the reason for the extraordinary acoustics of the theater in Epidaurus, says the magazine "Nature".
Discovered in 1881 on the Peloponnese, the ancient structure has the classic semicircular shape of the ancient Greek amphitheater and has 34 rows of stone seats. The Romans later added a further 21 lines.
The facility has incredible acoustics: no microphones, amplifiers and speakers, replicas of aktaorite hear better and last lines, located approximately 60 meters from the scene.

 Physicists and Nico Deklerk Cindy Dikeyzar from Georgia Institute of Technology in Atlanta (USA) believe that the key lies in the location of terraced stone rows, which are located viewers.
Estimated their amphitheater was built so that it works as an acoustic filter which passes high frequency sounds, usually produced by the actors' voices, while muted low frequency, which in ancient times and today constitute the background noise generated by the public ( murmur, cough, sniff, seeds or hatching of blissfully snore).
Deklerk allow this incredible opportunity to effect was made accidentally by the ancient architects, amphitheater built in the 4th century BC.

 Very soon, however, he was assessed with dignity and became a standard in the construction of theaters across Ancient Greece and Rome. During the 1st century BC. Roman expert in architecture Vitruvius praised the skills of the Greeks to apply the science of harmony in the construction of theaters so that the voices of the actors to not only reach the ears of all present, but to caress their hearing.
Later authors explain the magnificent acoustics of the theater Epidaurus with the wind which blows mainly from stage to audience.
Others believe that the key lies in the peculiar rhythm of the actors' lines in the ancient Greek tragedies and comedies.

 There is also a theory that the actors wore masks because they serve as their speaker.
Nobody could explain why, however, even today, when the stage performances of Epidaurus there, they were postponed because of wind.
Deklerk Dikeyzar and suggest that the effect is related to the particular way in which the corrugated surfaces reflect sound. For several years it is known that they filter sound waves so amplified waves with certain frequencies.

Similarly, the microscopic folding the wings of butterflies reflect light with a wavelength, which makes their specific coloration. Serrated surface is sound insulation materials used in modern construction.
In a previous study Deklerk proves that a stepped Mayan temple in Mexico can make the steps and clapping of visitors to sound like the chirping of birds or rain.

Now his calculations show that the terraced rows of stone benches in the amphitheater Epidaurus reflect the sounds so that those below 500 hertz are silenced more than those with higher frequency.
Not a problem for viewers of the last row can hear clearly the voices of actors, since auditory perception human brain demonstrate the ability called "virtual tone". Through her, he added some of the missing lower frequencies to higher perceived to reproduce the real sound.
Although the level of modern sound equipment, physicists believe that the inventions of the ancient architects acoustic filter can still be used in the construction of stadiums and outdoor theaters.