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Author Topic: Mystery of Greek Amphitheater's Amazing Sound Solved  (Read 2810 times)

zmix

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Mystery of Greek Amphitheater's Amazing Sound Solved
« on: April 06, 2007, 01:21:23 pm »

Mystery of Greek Amphitheater's Amazing Sound Finally Solved

By Tom Chao
LiveScience Staff Writer
posted: 05 April 2007
1:30 pm ET



Cut the chatter! The ancient mystery surrounding the great acoustics of the theater at Epidaurus in Greece has been solved.

The theater, dating to the 4th century B.C. and arranged in 55 semi-circular rows, remains the great masterwork of Polykleitos the Younger. Audiences of up to an estimated 14,000 have long been able to hear actors and musicians—unamplified—from even the back row of the architectural masterpiece.

How this sonic quality was achieved has been the source of academic and amateur speculation, with some theories suggesting that prevailing winds carried sounds or masks amplified voices.

It's in the seats

Now, researchers at the Georgia Institute of Technology have discovered that the limestone material of the seats provide a filtering effect, suppressing low frequencies of voices, thus minimizing background crowd noise. Further, the rows of limestone seats reflect high-frequencies back towards the audience, enhancing the effect.

Researcher Nico Declercq, a mechanical engineer, initially suspected that the slope of the theater had something to do with the effect.

“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,” Declercq said. “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.”

However, experiments with ultrasonic waves and numerical models indicated that frequencies up to 500 hertz (cycles per second) were lowered, and frequencies higher than 500 hertz went undiminished, he said.

Acoustic traps

The corrugations on the surface of the seats act as natural acoustic traps. Though this effect would seem to also remove the low frequencies from the actors' voices, listeners actually fill in the missing portion of the audio spectrum through a phenomenon known as virtual pitch. The human brain reconstructs the missing frequencies, producing the virtual pitch phenomenon, as in listening to someone speaking on a telephone with no low end.

The findings are detailed in the April issue of the Journal of the Acoustics Society of America.

Amazingly, the Greek builders of the theater did not themselves understand the principles that led to the exceptional audibility of sound from the stage.

Attempts to recreate the Epidaurus design never quite matched the original. Later seating arrangements featured other materials, such as wood for the benches, an approach which may have ultimately derailed the design duplication effort.

jimmyjazz

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Re: Mystery of Greek Amphitheater's Amazing Sound Solved
« Reply #1 on: April 06, 2007, 04:03:24 pm »

Don't the audience members pretty much render the seats "nonexistent"?
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franman

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Re: Mystery of Greek Amphitheater's Amazing Sound Solved
« Reply #2 on: April 08, 2007, 10:03:31 am »

Interesting.. I would assume that a reasonable amount of LF hits the seats regardless of the audience.. Where is the rolloff (crossover)?? Good question... but, it's a reasonable explanation... pass the midrange and filter the LF.. this should increase intellegibility.

Anyway.. look, it was published in the JASA.. it must be right!! (you know, I read it in the NY Times, it has to be true!)... Twisted Evil    Very Happy    Shocked    Shocked
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jimmyjazz

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Re: Mystery of Greek Amphitheater's Amazing Sound Solved
« Reply #3 on: April 08, 2007, 09:45:32 pm »

The characteristic length of a seat is about 0.5 meter.  How could frequencies with wavelengths longer than that distance "see" the seats?  If I'm right, then seat geometry shouldn't affect frequencies below about 700 Hz or so.
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franman

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Re: Mystery of Greek Amphitheater's Amazing Sound Solved
« Reply #4 on: April 09, 2007, 09:36:12 pm »

Jimmy.. yeah, intuitively that would be a good analysis.. I wonder if the seat "assembly" consisting of many rows of seats is more significant that any one seat. In any amphitheater seats make up the better part of the audience area, right.. So it stands to reason (to me) that the construction, material and actual configuration of the seating would have a significant impact on even very low frequency decay, etc...

The way I'm seeing it, it's not the size of any one seat, or row of seats, it's the entire audience area that has a major affect on the behavior of the LF.. that makes sense to me?? But, what do I know.. If it's not a room with speakers in it, I'm not in my element??!!  Twisted Evil

(just kidding, I like all of these rooms where sound is significant!!)
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jimmyjazz

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Re: Mystery of Greek Amphitheater's Amazing Sound Solved
« Reply #5 on: April 09, 2007, 11:25:52 pm »

Very good point, F.  If the rows were clustered in groups of a few rows or more, perhaps separated by flat aisles that run circumferentially, then that grouping might be signficant at longer wavelengths.  I never thought of that.
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CHANCE

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Re: Mystery of Greek Amphitheater's Amazing Sound Solved
« Reply #6 on: May 18, 2007, 09:10:59 am »

If you do a search for "the golden formula", you will find some amazing information. I first discovered this when "Westlake Audio" designd my CR & TR. They (supposedly) used this golden formula.
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Travis Engler

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Re: Mystery of Greek Amphitheater's Amazing Sound Solved
« Reply #7 on: June 06, 2007, 04:57:20 pm »

I guess the point is that you need the audience to be sitting on huge bass traps. It's brilliant because usually that area is just a lot of wasted space.  If most new arenas allowed the bass to bleed through the seats and reflected the highs they probably wouldn't sound like ass.  
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