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Author Topic: Inner Shell / Outer Shell  (Read 2371 times)

jfrigo

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Inner Shell / Outer Shell
« on: August 26, 2006, 03:56:55 pm »

All agree that symmetry inside the control room is very important. The geometry of the inner shell should certainly be symmetrical; however, some designers and/or acousticians prefer the outer shell to be asymmetrical. What's your opinion on the subject? I know there will be variables with the rigidity and mass of each shell, and with the use of cavities for bass trapping. Any comments as to advantages or disadvantages, real or imagined, between the two approaches - symmetry in both vs symmetry inside only?
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franman

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Re: Inner Shell / Outer Shell
« Reply #1 on: August 26, 2006, 09:52:23 pm »

If by Inner Shell you mean the inner isolation wall, or inner drywall assembly, assuming it's multiple layers and is a LF boundary, yes it's symmetry is important to me...

If by Outer shell you mean any heavy partition behind the above Inner shell, than I do not feel the symmetry is any where near as important. Its nice, but we never do any modal calculations on outer shell, so it they are not perfectly symmetrical because of other design considerations, than so be it.


IF by Inner shell you mean a framed system of acoustic treatments such as a stretched fabric or Slat wall, then yes the symmetry is important and this would imply that the "outer shell" was the drywall (or other) partition that is the first significant boundary to LF sound.... then YES the symmetry of this shell is equally important...

Wow.. does that make any sense??
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Francis Manzella - President, FM Design Ltd.
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jfrigo

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Re: Inner Shell / Outer Shell
« Reply #2 on: August 26, 2006, 11:53:48 pm »

I meant inner shell to be framing and drywall, not treatments or finishes on top of that structure. Outer shell would be the outer room in a "room within a room" type construction.

Some designers feel that an asymmetric outer shell is actually good for low end behavior inside the room. If the inner shell was too rigid and massive, I think it wouldn't matter what the outside shell's shape was, but with framing and drywall, enough energy may get through to a more rigid and massive outer shell and be returned, so I suppose the geometry of the outer shell could theoretically affect the low end response within the room.

However, I think from a practical viewpoint that it would be of little concern, and I'm not sure that the asymmetric outer shell would help very much. This seems like one of those things that is neat in theory, but is not very significant in practice.

Thanks for your thoughts!

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franman

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Re: Inner Shell / Outer Shell
« Reply #3 on: August 27, 2006, 03:06:36 pm »

Jay,

Yep I would tend to agree... theoretically interesting, but???
Also, if the Inner shell was to allow some VLF energy out (which all will do) and then it was to interact with the outer shell and have to transmit back into the primary shell, I would think it's level would be so attenuated by that time as to be insignificant in it's interaction within the room....
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Francis Manzella - President, FM Design Ltd.
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Larrchild

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Re: Inner Shell / Outer Shell
« Reply #4 on: August 27, 2006, 03:54:53 pm »

http://www.saecollege.de/reference_material/images/Corner%20Plan.gif
Seems like, in the real world, you're always doing something like this, eh? Using the outer shell you have, and dividing it up.

So the modes on the outer shell can only get energized if the inner wall has transparency at those freq's. So I guess the denser and more trapped, the inner shell is, the less it's an issue. I bet there are a few rooms out there that are getting outer-boundry modes back thru the inner walls at the lowest freq's. Say 20-40 hz.

Photo courtesy of SAE College.de
http://www.saecollege.de/reference_material/pages/Variable%2 0Plans.htm

I really like the Kitchen/Vocal Booth idea btw, people get hungry singin'
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franman

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Re: Inner Shell / Outer Shell
« Reply #5 on: August 27, 2006, 04:02:04 pm »

yeah.. make me a snack while you're singin that chorus again please!!
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Francis Manzella - President, FM Design Ltd.
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