# HT Wall Construction Question



## hat_man (Feb 19, 2009)

I am considering building my home theater with the room within a room method. When constructing your framing/stud walls of your home theater, and one or more walls are along or next to a concrete basement wall, what recommendations do you have for what to do for the side of the stud wall that faces the concrete, the side you can't see? Do you leave it open to the concrete? Install one (or more) layers of drywall on that side? How does that method effect sound control or acoustics? Thanks!


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## bpape (Sep 14, 2006)

When doing the room in a room, you always leave the inner wall's outside with nothing on it and fill the cavity with insulation. This still applies to the times it's just facing concrete.

Bryan


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## keelay (Dec 11, 2008)

I second the response. The insulation is better than any drywall or other standard construction material for it's absorption properties and since there are less materials it will likely reduce cost.

Kyle


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## Space (Jul 18, 2007)

I agree.

But.

John Sayers uses a technique called the "inside-out-wall" usually employed as a means to save floor space. As some of you already know, the mass(sheetrock) is nailed to what will be the side of the framing facing the exterior wall, in your case, the concrete wall.

Then you have the open framed area to install your damping / vibration reducing insulation to be covered with fire retardant fabric.

From the inside of the room out you would have:

insulation>framing>sheetrock>air >concrete.

The positive effect is the floor space you save with this type of construction.

The negative effect is loose of isolation due to reduced air/spring size.

Still it is mass/air/mass.

Just a thought.

Brien


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## bpape (Sep 14, 2006)

I don't know who posted that but it's not at all correct - sorry. While you do get some mass there, it's all outside the framing members. In addition, you're seriously shrinking the cavity depth between your mass and the mass behind it - which will raise the resonant frequency of the cavity - exactly the opposite of what we're trying to accomplish.

Also, you would end up with a room that's WAY too dead by effectively having every surface 100% absorbant.

Bryan


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## Space (Jul 18, 2007)

bpape said:


> I don't know who posted that but it's not at all correct - sorry. While you do get some mass there, it's all outside the framing members. In addition, you're seriously shrinking the cavity depth between your mass and the mass behind it - which will raise the resonant frequency of the cavity - exactly the opposite of what we're trying to accomplish.
> 
> Also, you would end up with a room that's WAY too dead by effectively having every surface 100% absorbant.
> 
> Bryan


Names right on the post Bryan. 

You are not familiar with this version and maybe more explanation would help you to understand it better.

The "way to dead" part is overcome by reflective slats on the interior side of the room:
http://www.saecollege.de/reference_material/audio/pages/Walls.htm


In any event, the point is to show there exists another option outside of the singular way described and subscribed to by others above.

If you have further questions you can take them up with the developer: http://www.johnlsayers.com/


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## bpape (Sep 14, 2006)

Sorry - wasn't referring to you - I meant at Sayers. Yes - you can do it but to me, it doesn't seem logical to move the mass outside to save space - and then have to turn around and put slatting on the walls to avoid being over dead - and taking up the same amount of space effectively. 

If you also look at some of the drawings they have there in the SAE link, you'll see places where they're showing what is effectively a triple leaf which is known and almost universally accepted to be a bad thing.


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## Space (Jul 18, 2007)

I do agree that the space saving feature may not actually materialize for the end product, but it is still an option. But the triple leaf doesn't exist on the page I linked. It may look that way, but it isn't there due to several things, e.g. breathable cloth as the final boundary, separated wood slats as the final wall panel, etc.

A triple leaf is like the red headed step child. It is misunderstood. It isn't something you >want< to build into your studios and home theaters, but there are many cases where it exists. Most often in the ceiling area of a room -in-room design where the roof as part of the equation is never looked at.

The reduction, as I understand it, in the low frequency part of the spectrum is not desirable.
It is not uncommon to see a room build as a composite of a 1 leaf(floor), 2 leaf(wall) and the 3 leaf(ceiling roof).

In any event, like I said, just a thought.


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## Ted White (May 4, 2009)

Bryan is right in that you would want to have the air cavity as large as practical. And also have the framing decoupled from the original structure. I've been involved in several Rives Audio designs where similar diffusors are installed in the ceiling joist space. This leaves us with no classin Mass-Air-Mass system. 

In this instance sound control using the slat diffusor method outweighed the sound isolation need. Everyone has different needs and parameters. In these instances, we added more damped mass to the underside of the existing subfloor before the diffusors were installed.

In the case of the wall, it would be advisable to decouple the wall frame from the foundation, and move as far away from that foundation as possible to gain air cavity volume. Add uncompressed fibegflass between the concrete and the frame. Add as much (damped) drywall as practical to that outside surface of the newly framed wall. Then proceed with the diffusor treatments.


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