Stalactite Ceiling Treatment

[WMcD]

Does anyone know the source of the ceiling acoustic treatment we saw at Indy? It looked like rectangular stalactites in styrofoam, or a model of city buildings.

I don't see it on thee Auralex site. They provided a lot of the other treatment and you can find info on their website.

For years people here and elsewhere have been point to room problems. Now I start to wonder if any speaker doesn't sound good in room like that, described as 75% dead. Others have wondered about this before.

[scriven]

Here is some of it. The price puts it out of my range! BTW, nice cartoon!

http://www.sweetwater.com/store/category/c670

[Daddy Dee]

Great cartoon Gil! Thanks.

[michael hurd]

I believe that it is called "skyline" by RPG.

[WMcD]

Thank you one and all. Yup, that is indeed the stuff.

The Master Handbook of Acoustics has a good section about RPG designs and I'll have to look it up. This may be the one which gives hemispherical diffusion.

I don't know of any cheap source of styrofoam blocks to make a homebrew. Right now I can't think of a way to glue together styrofoam peanuts to make it. Wouldn't that be something to do after braiding CAT-5.

Best,

Gil

[DrWho]

The synergy room had the Auralex T' Fusors, but everywhere else had the RPG skyline panels.

The room is responsible for well over 50% of the sound, so at best a speaker that is 100% better (twice as good) in the same room can really only sound 50% better. Now I know these are just numbers and have no bearing on the real issue, but the idea is that the room is responsible for so much of the sound that minor changes get masked by problems within the room. Heck, put the khorns in the wrong room and the bose acoustimass cube thing in the right room and I bet you could make the bose sound way better.

I have no doubt that what we heard at the pilgrimage was mostly due to the rooms we were in. That's no discredit to klipsch though because their speakers really did shine...which means no flaws in the speakers were being masked (at least I don't think they were trying to be sneaky like how bose is at their demo stores).

[Mighty Favog]

Here's the link to it/them.

http://www.rpginc.com/products/skyline/

[IB Slammin]

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On 7/2/2005 6:07:33 PM William F. Gil McDermott wrote:

Thank you one and all. Yup, that is indeed the stuff.

The Master Handbook of Acoustics has a good section about RPG designs and I'll have to look it up. This may be the one which gives hemispherical diffusion.

I don't know of any cheap source of styrofoam blocks to make a homebrew. Right now I can't think of a way to glue together styrofoam peanuts to make it. Wouldn't that be something to do after braiding CAT-5.

Best,

Gil

Gil,

Are they saying that size and placement of the cubes are a calculated patern and not random?

Regards,

Terry

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[WMcD]

IBS,

No, my understanding is that they are not random. There is a great amount of precision.

My understanding is imperfect so I can't give a good explanation right now.

Let me start off by saying that we're trying to avoid a normal reflection off a hard surface, which would be on axis. We'd like to have it spread out, off axis. Then maybe something else will absorb it.

The more common form of this RPG system works in two dimensions, but this may obscure the issue in a way.

The typical RPG is a section of slots which vary in depth. The sound pressure goes in, then is reflected from the bottom of the "well", and comes out again. This causes a time delay in the reflection. One of the typical ways of causing a phase change is delay. This is an application.

That may deserve a more expansive explanation. (If I may get pedantic. Please excuse.) Suppose you have a big hard wall with a 1 foot diameter pipe stuck which is four feet long and closed off at the bottom. Sort of a wishing well.

There is a normal reflection off the wall from the sound pressure against it. There is also a reflection from the bottom of the well, but it is delayed relative to the wall's reflection. We're not absorbing the energy at all. We're just messing with time and phase, because of the delay. Maybe part of this can be used to redirect the reflection.

Consider that if you have two point sources which are in phase, they add up to a max when you're equidistant from them (i.e. you're sitting on axis). Analogize that to a flat surface. And then again, a mirror which is facing you.

But consider what happens if the two sources are out of phase at the transmitting end because one is somehow delayed. (In our case, because of the delay from the well.)

Then they don't add up to a max when you're on axis. But if you move off axis, one source is closer than the other. The path length difference creates a delay which compensates for the initial delay from one of the sources.

So, by using a delay or phase shift, we've created a maximum adding, off axis. (This is the big point.) This is like tilting the mirror. So the sound pressure is being redirected off axis simply because of the delay! This is diffusing the sound to another part of the room which the wall, itself can't do.

The tricky part is making this phased array of reflections work over a wide range of frequencies. Every little well has to have a certain depth and be placed properly.

You can see that the well type diffusers are really just creating a ragged, if precise in raggedness, reflecting surface.

The skyline type seems to be doing the same in a different way. Rather than digging holes, it is creating mountains. Maybe the valleys in the mountains are indeed the same as wells.

I'll eventually look it up and may post the section from the Master Handbook of Acoustics. BTW the book is an excellent work, very readable, not too much math.

Gil

[mikebse2a3]

Gil Said:

The skyline type seems to be doing the same in a different way. Rather than digging holes, it is creating mountains. Maybe the valleys in the mountains are indeed the same as wells.

------------------------------------------------

Gil the valleys are the same as the wells in the One Dimensional diffuser.

First www.rpginc.com is a great site for articles to learn about acoustics, their products and their designs. They heavily research and test their designs to see that they actually meet their design goals.

RPG also makes a Two Dimensional diffuser called the omniffusor which if you look at it you will see the walls used just like the orginal One Dimensional QRD diffusor.

The Skyline has one very beneficial feature because it is a based on Primitive Root Number Theory and that is the "specular suppression of the incidence sound wave" which means that if you use them say at points in the room where you would see a mirror image reflection of the sound source(SUCH AS THE SPEAKER)then the interfering reflection would be suppressed and the energy used to create a more diffuse sound field. The most popular recomended way to deal with these early mirror image reflection points has been the use of absorption but often this can create a dead or unnatural sound. I have been in the process of using some of these panels and so far in my small room I definitly feel it is better to use diffusion than absorption but like any acoustical treatment where they are placed and their distance from source and listener are factors that need to be considered also.

mike

[sunnysal]

gill, here is a similar product from rpg that uses holes instead of the "buildings" it appears that it accomplishes the same thing. it´s called the hemiffuser:

try this link for more options:

http://www.rpginc.com/residential/cinemusic-products.htm

regards, tony

[IB Slammin]

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On 7/3/2005 5:30:45 PM William F. Gil McDermott wrote:

IBS,

No, my understanding is that they are not random. There is a great amount of precision.

My understanding is imperfect so I can't give a good explanation right now.

Let me start off by saying that we're trying to avoid a normal reflection off a hard surface, which would be on axis. We'd like to have it spread out, off axis. Then maybe something else will absorb it.

The more common form of this RPG system works in two dimensions, but this may obscure the issue in a way.

The typical RPG is a section of slots which vary in depth. The sound pressure goes in, then is reflected from the bottom of the "well", and comes out again. This causes a time delay in the reflection. One of the typical ways of causing a phase change is delay. This is an application.

That may deserve a more expansive explanation. (If I may get pedantic. Please excuse.) Suppose you have a big hard wall with a 1 foot diameter pipe stuck which is four feet long and closed off at the bottom. Sort of a wishing well.

There is a normal reflection off the wall from the sound pressure against it. There is also a reflection from the bottom of the well, but it is delayed relative to the wall's reflection. We're not absorbing the energy at all. We're just messing with time and phase, because of the delay. Maybe part of this can be used to redirect the reflection.

Consider that if you have two point sources which are in phase, they add up to a max when you're equidistant from them (i.e. you're sitting on axis). Analogize that to a flat surface. And then again, a mirror which is facing you.

But consider what happens if the two sources are out of phase at the transmitting end because one is somehow delayed. (In our case, because of the delay from the well.)

Then they don't add up to a max when you're on axis. But if you move off axis, one source is closer than the other. The path length difference creates a delay which compensates for the initial delay from one of the sources.

So, by using a delay or phase shift, we've created a maximum adding, off axis. (This is the big point.) This is like tilting the mirror. So the sound pressure is being redirected off axis simply because of the delay! This is diffusing the sound to another part of the room which the wall, itself can't do.

The tricky part is making this phased array of reflections work over a wide range of frequencies. Every little well has to have a certain depth and be placed properly.

You can see that the well type diffusers are really just creating a ragged, if precise in raggedness, reflecting surface.

The skyline type seems to be doing the same in a different way. Rather than digging holes, it is creating mountains. Maybe the valleys in the mountains are indeed the same as wells.

I'll eventually look it up and may post the section from the Master Handbook of Acoustics. BTW the book is an excellent work, very readable, not too much math.

Gil

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Thanks Gil. If each mountain and valley are precise in size and location, I can see why this stuff is so expensive!! Granted the poly is extruded, but the sheet does not look like it came from a mold.

Terry