The Mystery Of The Greek Amphitheater Solved

For centuries acousticians have argued over the secret to the excellent acoustics at the amphitheater of Epidaurus in Greece.

Crowds of up to 14,000 people have been able to hear the actors and musicians perform in the theater completely un-amplified, even in the back row, but yet science has been able to say exactly why that was possible.

The amphitheater, which dates back to the 4th century BC, is a masterpiece of architecture by Polykleitos the Younger, but its acoustics have never been duplicated (even by Polykleitos) regardless of the increasing sophistication of measurement equipment at the disposal of the modern acoustician.

Researchers at the University of Georgia have finally unlocked the secret though - it's all in the seats!

In findings presented in an issue of The Journal of The Acoustics Society of America, the scientists involved in the research found that the limestone used in the seats provide filtering and absorption, thereby decreasing crowd noise and low frequencies that might interfere with the performance. All the frequencies below 500Hz are attenuated.

That's not all. It seems that the slope of the seats reflect the high-frequencies back towards the audience, making it easier for them to distinguish the sounds of the performers.

Then there's the fact that corrugations of the seats act as bass traps, which then lead to the listener filling in the frequencies psycho-acoustically, just like what happens when listening to an MP3.

So lets see - absorption, bass traps, reflection angles - sounds like modern recording studio building techniques to me. It just goes to show that no matter how things evolve, they still manage to stay the same.

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The 3 Building Blocks Of Acoustic Treatment

While soundproofing the space where you have your recording gear set up can be an expensive and time consuming proposition, treating the acoustics of your room luckily can be quite the opposite. Believe it or not, it’s not that expensive and can be done in only a matter of hours if you have all the building blocks on hand.

So what are these building blocks? Here's an excerpt from my Studio Builder's Handbook (written with Dennis Moody) that explains just what they are.

"Acoustic treatment for your room is built around three main components: acoustic panels, bass traps, and diffusers. Let’s take a brief look at each.

Acoustic Panels
Acoustic panels are the major way that reflections are kept from bouncing around the room. If your walls are hard (meaning there’s no absorption), these reflections are going to cause certain frequencies to cancel themselves out as they bounce around, causing those unwelcome dips and peaks in the room response as well as an uneven reverb decay time.

You can think of an acoustic panel as a very large picture frame that has sound absorbing material inside instead of a picture. Although you could permanently attach the sound absorbing material to the wall (like most commercial studios do), using a sound panel allows you to move it as needed and even take it with you if you move.

Acoustic panels are easy and inexpensive to make (check out this video on my YouTube channel for information how), but they’re also available pre-made from a variety of companies like Ready Acoustics, GIK Acoustics, RealTraps.com, ATS Acoustics, MSR, AV Room Service and many more.

Bass Traps
Most control rooms use what’s known as a “bass trap” to control at least some of the low frequency energy in the room. In most rooms, the main problem at low frequencies is due to one or more deep nulls or peaks in the range anywhere from 40 to 200Hz. Bass traps reduce the depth of the nulls and attenuate the boomy sounding peaks, and the overall response of the room is flatter as a result. Even though your brain intuitively thinks that you lose low end by attenuating it, the room will actually sound tighter and more predictable, with less change in the response when you move away from the sweet spot.

Bass traps work best in corners because bass tends to collect there, but they can also work well spaced off the front and rear walls. Since bass is omnidirectional, the traps don’t have to be paired or symmetrically placed, although believe it or not, the smaller the room the more you will need. The most effective ones extend from floor to ceiling. If that can’t happen, the next most effective method is to just treat the 8 individual corners of the room.

As with acoustic panels, pre-made bass traps are made by a number of manufacturers like the ones mentioned above.

Diffusers
A diffusor scatters sound to reduce the direct reflections from the speakers back to the listener. There are two types of diffusers; 2D and 3D. A 2D diffuser (as seen on the left) scatters the reflections in the same single plane that they were received, while a 3D diffusor scatters it in random directions at random times. If made well, the 3D diffuser is better at scattering the reflections, but more difficult to build so it’s more expensive.

While diffusers can be used anywhere in the room that doesn’t already have an acoustic panel, a common strategy that’s used by many large commercial studios is to use a diffusor on the rear wall. Doing this is controversial, as there are as many designers who believe that the rear wall should be non-reflective as there are that believe it should be diffuse.

In small rooms where the rear wall is closer than six feet from the listening position, you're likely to have more success trying to absorb the sound with deep traps than you are diffusing it. A bookshelf filled with books is a great natural diffusor (and adds some absorption as well), but shelves randomly filled with objects, or small angle wood blocks can work too. Companies like RPG, Real Traps and MSR also make both off-the-shelf and custom diffusors as well.

With any of these acoustic components, you don't need to spend a fortune to achieve tangible results. That said, it isn't easy to predict in advance just how much of an improvement there will be for any given approach (even for the pros studio designers), so some experimentation is required."

You can find out a lot more about how to build a home studio effectively and inexpensively by consulting The Studio Builder’s Handbook. You can also read some excerpts from this and my other books on excerpt part of my website.

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Any purchases made through our Amazon links help support this blog at no cost to you (just click here).

The 3 Components Of Acoustic Treatment

While soundproofing the space where you have your recording gear set up can be an expensive and time consuming proposition, treating the acoustics of your room luckily can be quite the opposite. Believe it or not, it’s not that expensive and can be done in only a matter of hours if you have all the building blocks on hand.

So what are the building blocks? Acoustic treatment for your room is built around three main components: acoustic panels, bass traps, and diffusers. Let’s take a brief look at each.

Acoustic Panels
Acoustic panels are the major way that reflections are kept from bouncing around the room. If your walls are hard (meaning there’s no absorption), these reflections are going to cause certain frequencies to cancel themselves out as they bounce around, causing those unwelcome dips and peaks in the room response as well as an uneven reverb decay time.

You can think of an acoustic panel as a very large picture frame that has sound absorbing material inside instead of a picture. Although you could permanently attach the sound absorbing material to the wall (like most commercial studios do), using a sound panel allows you to move it as needed and even take it with you if you move.

Acoustic panels are easy and inexpensive to make (check out this video on my YouTube channel for information how), but they’re also available pre-made from a variety of companies like Ready Acoustics, GIK Acoustics, RealTraps.com, ATS Acoustics, MSR, AV Room Service and many more.

Bass Traps
Most control rooms use what’s known as a “bass trap” to control at least some of the low frequency energy in the room. In most rooms, the main problem at low frequencies is due to one or more deep nulls or peaks in the range anywhere from 40 to 200Hz. Bass traps reduce the depth of the nulls and attenuate the boomy sounding peaks, and the overall response of the room is flatter as a result. Even though your brain intuitively thinks that you lose low end by attenuating it, the room will actually sound tighter and more predictable, with less change in the response when you move away from the sweet spot.

Bass traps work best in corners because bass tends to collect there, but they can also work well spaced off the front and rear walls. Since bass is omnidirectional, the traps don’t have to be paired or symmetrically placed, although believe it or not, the smaller the room the more you will need. The most effective ones extend from floor to ceiling. If that can’t happen, the next most effective method is to just treat the 8 individual corners of the room.

As with acoustic panels, pre-made bass traps are made by a number of manufacturers like the ones mentioned above.

Diffusers
A diffusor scatters sound to reduce the direct reflections from the speakers back to the listener. There are two types of diffusers; 2D and 3D. A 2D diffuser (as seen on the left) scatters the reflections in the same single plane that they were received, while a 3D diffusor scatters it in random directions at random times. If made well, the 3D diffuser is better at scattering the reflections, but more difficult to build so it’s more expensive.

While diffusers can be used anywhere in the room that doesn’t already have an acoustic panel, a common strategy that’s used by many large commercial studios is to use a diffusor on the rear wall. Doing this is controversial, as there are as many designers who believe that the rear wall should be non-reflective as there are that believe it should be diffuse.

In small rooms where the rear wall is closer than six feet from the listening position, you're likely to have more success trying to absorb the sound with deep traps than you are diffusing it. A bookshelf filled with books is a great natural diffusor (and adds some absorption as well), but shelves randomly filled with objects, or small angle wood blocks can work too. Companies like RPG, Real Traps and MSR also make both off-the-shelf and custom diffusors as well.

With any of these acoustic components, you don't need to spend a fortune to achieve tangible results. That said, it isn't easy to predict in advance just how much of an improvement there will be for any given approach (even for the pros studio designers), so some experimentation is required.

You can find out a lot more about how to build a home studio effectively and inexpensively by consulting The Studio Builder’s Handbook, which I wrote with Dennis Moody. You can also read some excerpts from the book on my website.

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