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[Phillip_Graham]

Mac Kerr wrote on Mon, 27 April 2009 16:07

Phillip Graham wrote on Mon, 27 April 2009 15:06 Mac Kerr wrote on Sat, 25 April 2009 17:46 How the array behaves is very dependent on frequency. It is also very dependent on the environment. The difference delay makes with no walls is easy to understand, and seems very controlled. When you add in the reflecting surfaces of the room the whole picture changes. It is easy to see why it is not so easy to make this all work in the real world. Mac Hey Mac, Two points of subtlety, even though the point of these graphs should not be lost on anyone. First, MAPP gives no consideration of the third dimension, which can/will change the locations of the nodes and antinodes,  The diagrams can be thought of only as accurate in 2d. True, I think I mentioned that here.

Sorry I did not see that.  I guess the point I am trying to drive home is that 2d constrained solutions of the differential equations involved here is going to produce a very different distribution of modes than what is allowed by the 3d shape.  The changing of the distributions of the solutions to these types of equations is the very essence of "nanotechnology" that people blather on about.

Mac goes on

Phillip Graham wrote on Mon, 27 April 2009 15:06 Second, MAPP gives you no control of the stiffness and losses of the room boundaries.  I don't know the values that Meyer has chosen, but they may or may not reflect reality.  Simple (ie unrealistic) boundary conditions is typically computationally expedient, so that might be what Meyer is doing. I am sure Perrin or one of their other modeling guys could chime in on that. Mapp does give you some control over the surface as shown in the image below. What I have not been able to make it do is make the architectural guidelines be surfaces. As far as I can tell you are limited to the box shape, although you can set the dimensions of the box. Since it is not 3D those details may be irrelevant anyway. Mac

A rectangle (technically not a box) is computationally expedient for these situations, because you can use simple (eg periodic) boundary conditions.  Also the solutions are generally stable.  I wonder if the Meyer materials choices are simply changing absorption at the boundaries, or if they are doing more?

PS: The boundaries in most "real" spaces are very "floppy" in that they have low stiffness, moderate absorption, and can re-resonate with tones of their own.  From what I saw presented by WSDG in "Small Room Acoustic"' at the SF AES is that properly doing these numerical solutions for real spaces is really challenging.

PPS: We have a large church here in Atlanta that has a very loud Sunday service, and very stringent requirement for noise because of its proximity to multi-million dollar condo towers.  This room has poured concrete floor and ceiling, and very stiff multi-wall construction with air gaps to minimize noise.  Its low frequency modal response is much more "theoretical" than most rooms due to its massive and stiff boundaries.  Its a fascinating room for a case study in low frequency physical acoustics.

[Phillip_Graham]

Kevin Windrem wrote on Sat, 25 April 2009 13:35

Christian Tepfer wrote on Fri, 24 April 2009 11:24 ... Spacing in between the subs eases the beam as well... MAPP seems to indicate increasing spacing between subs (with no delay tapering) NARROWS coverage (until the spacing gets too large, then you start seeing cancellation). 12 tight packed subs is already pretty narrow.

Kevin, this is correct globally in the half-sphere of coverage, but what Christian is suggesting can work practically for narrowing out the main coverage lobe.

Say you have a festival setting where all of the patrons are essentially contained in a rectangle as wide as the main stage (IOW in between the PA hangs).  Here, if you don't have enough subs to make a solid horizontal array across the entire stage front, but instead you spread them out a few feet on center, the practical result will be a wider main lobe (in between the PA towers).

If the audience spills well outside of this width, like in the arena being discussed, then of course a different sub deployment is in order.

So its possible for you both to be right depending on the needed deployment

[Tom Young]

Thanks for pointing that out.

It's more akin to Django than (name your favorite 6 or 12 string guitar picker).

I'm glad you don't do drugs, Mike

[Ivan Beaver]

Tom Young wrote on Mon, 27 April 2009 18:16

Thanks for pointing that out. It's more akin to Django than (name your favorite 6 or 12 string guitar picker). I'm glad you don't do drugs, Mike

Frank Zappa didn't do drugs either, and you have seen/heard his work  
Another one snuffed out to early

[Luis Pinzón Arroyo]

Could anybody post a closer photograph of those CLAIR's subwoofers please?

A pdf with it's specifications could help too.

Thanks.

Just in advance: I'm not of the "cloning guy" type.

This is a jpeg file of what I do:

It's made with 4 EAW's SB-1000 and I name it  "Wide Cardioid Subwoofer"

[Evan Kirkendall]

There are no published specs for those subs, but here's a closer shot of them:






FWIW- We have the subs center clustered with them now delayed and life is good. The bass spreads out a lot more, and still hits plenty hard up the middle. I think this is what we're going to stick with.



Evan

[Christian Tepfer]

Evan, this is a very interesting concept by Dave Rat. He controls coverage by side subs with delays adjusted to the desired coverage. (narrow, wide)
Scroll down through the japanese menu until you reach the sound nerd speak

http://www.ratsound.com/cblog/archives/232-Day-297-March-16- Fly-to-Japan.html

[Stephen Payne]

Ivan Beaver wrote on Fri, 24 April 2009 07:54

Evan was running the screaming girls (in the audience) WAAAYYY to hot!

That's all that matters

[Karl P(eterson)]

Or his latest post, which discusses the same thing right here.

http://www.ratsound.com/cblog/

Karl P

[Bennett Prescott]

So one of his requirements is that he not use cancellation techniques (read: cardioid) but then he goes and does exactly that?

[ProSoundWeb Community]