John Sayers' Recording Studio Design Forum Archive

Great! I was hoping you would say that.

Second question for today: I am revisiting the "inside out" wall in order to eek out some extra inches. But I wanted to have the open studs face to the unfinished utility space (see Detail 4). What happens if we have to add mass later? Can we only add additional drywall to the inner leaf (inside of the studio room) so we don't create a triple leaf situation? Does this mess up all our electrical boxes in the wall?

We have two windows at the top of the exterior wall. The existing windows will be sealed shut and an additional layer of fixed laminate glass will be at the "inner leaf." My question is about acoustics in the room. I was hoping to set these fixed glass to the outside of the window area - so there is a sill at the interior of the room. Is this going to be a negative for acoustics? Should the fixed glass be in the same plane as the inner leaf drywall? Thanks again for all this help.

I wanted to have the open studs face to the unfinished utility space (see Detail 4). What happens if we have to add mass later?

If you have access to that utility space, then you can add more mass by beefing up between the studs. In other words, cut strips of drywall just wide enough to fit neatly in the bay between each pair of studs, pressed up tight against the existing drywall. Hold that in place with cleats and seal around the edges with acoustic caulk.

I was hoping to set these fixed glass to the outside of the window area - so there is a sill at the interior of the room. Is this going to be a negative for acoustics?

It won't matter much for room acoustics, but it WILL affect your isolation! If the air gap is narrow, that drives up the resonant frequency of the cavity and therefor reduces low-frequency isolation. And since you cannot damp that part of the gap with insulation like you do for the rest of the wall cavity, the problem is even worse. If you need good isolation, you should aim to have the air gap behind the glass as big as possible. And the surface density of the glass needs to be at least the same as the surface density of the rest of that leaf, or preferably higher.

- Stuart -

Thanks again for the help. You are an invaluable resource!

I will be posting some new details ASAP. I need to focus some attention on the mini split system, the room layout and electrical outlets in the next round.

We want to get someone in to take care of the floors soon. We are looking in to skim coats or self leveling underlayments. For a 100 year old concrete floor it is in pretty good shape. The existing concrete creates a lot of dust - and we need to be able to get the bead of acoustic sealant to bond. Do you have any insight in to these options? It doesn't have to be beautiful - and we do have some area rugs to put down there. Our concerns are cost and bonding ability, plus we don't have any head room to spare. We don't want anything to start peeling in a year or so....

We are still working away here...we thought we were getting closer and now we feel even farther away....we started to think maybe we should get french drains just in case we get water in the basement? We've gotten water on that side once when we forgot to clean out our downspouts and leaders...we thought we need a french drain that had a flange against our existing flagstone foundation. This flange comes about 2" up the existing foundation wall and creates a 3/8" gap between the foundation wall and the floor (where the french drain is). The flange start in between our inner and outer leaves but then extend to the unfinished utility space around the exterior wall to our sump pit....in doing so, it passes outside our outer leaf. I think this is a problem....and then I thought maybe we could mount double layer of drywall at the interior side of our rigid insulation furring. But then I didn't know if this would create and triple leaf with our existing foundation wall....yikes. Help please...

Per your question about creating a triple leaf:

In order to create a triple leaf(3) you require a hard boundary and an air space, the hard boundary multiplied by three (3).

This would dictate in construction a hard boundary/an air space/ a hard boundary/ an air space/ a hard boundary.

Does that help some?

The framing and the depth that is revealed is considered as part of the air space. Like if you use a 2 inch by 4 inch stud, the nominal depth of the stud (3-1/2 inches) is part of an airspace.

You show a 1 inch airspace in the drawing. when you take into account the 3-1/2 inches of depth that the stud gives you, you have a 4- 1/2 inch air space from the back of the hard boundary on the interior to the back of the hard boundary of the exterior.

What you do not want to do is to make a hard connection in ANY way from the interior framing to the exterior framing.

Your current drawing reveals that you are about to do this type of coupling/flanking and that will not help you my friend.

Yes, it does help. Thank you for your response. I guess I am wondering if a leaf has to be "air tight" to function as a leaf. And if I have a third surface, outside the second leaf (like my existing foundation wall) which has air gaps (french drain flange, windows, joist cavities, etc = basically we don't hit every crack with green glue). Is still a hard surface none the less. Is it still creating a third leaf - or do the three hard surfaces have to be hard connected? Thanks again.

I guess I am wondering if a leaf has to be "air tight" to function as a leaf.

No, as long as there is an air gap between it and the next leaf, then it is a leaf. This is a very interesting read about how that actually works in practice:
http://forum.studiotips.com/viewtopic.php?t=1198

But I wouldn't worry too much about the things you mention: It sounds like they might not be problematic. But photos would help to understand what you are dealing with! I would be more concerned about fixing the flanking path that Brien mentioned, and getting your inner-leaf and outer-leaf sealed up absolutely air-tight, with as much mass as possible and a big air gap (which is as Brien described it: the distance between the hard surfaces of the leaves, inside the wall. Insulation counts as "air", since it mostly is air anyway...).


- Stuart -

Thanks for the responses. The linked article was great!
This is such a adventure. There is so much to learn and so many ways to try to get the best music room out of our yucky basement. We spend a lot of time going back and forth with the actual construction details....and I have yet another comparative question. Since our room is pretty small, and because we are already using isolation clips at the ceiling, I was wondering if we could go for isolation clips on 3 of the 4 walls in the room (excluding the foundation wall). If we had 2 layers of drywall with green glue, isolation clips, 2x4 stud wall decoupled from joists above with insulation, and then two layers of drywall with green glue between....would the sacrifice of the mass at the walls also sacrifice too much soundproofing?
Thanks in advance for your help...again...

And another question...about framing the inner and outer leaves - and specifically about needing to attach the top plate of the inner leaf. I've been reading back to other posts (like http://www.johnlsayers.com/phpBB2/viewt ... ce#p119859)

1. There is no need to fasten the top plate of the inner leaf or outer leaf to anything? We just bolt the bottom plate in to the floor, no fasteners at the top plate, and no fasteners at the corners? The ceiling membrane and the two adjacent walls provide enough lateral support?

2. What if our building inspector wants some fasteners - or if there is another need to provide attachment at the top plate. I've read about the following three techniques: attach the top plate to a resilient channel which is then attached to the underside of the floor about, creating a slip joint, or compressing some rock wool between the top sill and the underside of the floor (basically just making the framing so tight that it can't move out). The rock wool seems the "easiest" and least likely to get shorted out by a misguided screw....thought?

3. Door framing - Gervais' book suggests not to worry about total isolation of the leaves at the door frame. Priority is given to supporting the door. So does this mean it is ok to hard fasten (i.e. standard construction) one (or both) top plates to the ceiling here?

P.s. i just got a notice of a reply...so you may have just answered this simultaneously...if so, apologies - and sincere thanks!

Sole plates (bottom plates) must be bolted/screwed/nailed to the floor, as required by code. You might also need to support the tops of the walls with sway braces, once again as required by code.

attach the top plate to a resilient channel which is then attached to the underside of the floor about, creating a slip joint,

I wouldn't do that. It probably would not pass inspection, either.

or compressing some rock wool between the top sill and the underside of the floor (basically just making the framing so tight that it can't move out).

If the wool is compressed that tight, then it is a flanking path! So that would not be decoupled, and isolation would be poor.

Just use proper acoustic sway braces.

Another thing you could do: Swap the first layer of drywall for OSB: that strengthens the wall greatly, in sheer.


- Stuart -

Thanks Stuart.
I edited my post while you were responding. A question about framing the door...
Also, regarding the OSB - by "first layer" you mean the one mounted to the stud that is then covered with green glue and the second layer of drywall?

Also, regarding the OSB - by "first layer" you mean the one mounted to the stud that is then covered with green glue and the second layer of drywall?

Exactly. That also has the added benefit of providing a nailing-surface around the entire room, which makes mounting your acoustic treatment much easier: you don't need to go hunting for studs!


- Stuart -

I've been reading up on sway braces and OSB and wanted to ask a couple follow up questions.

OSB - By incorporating OSB, we make the walls stiffer. But they are also making them heavier. Do we need to incorporate sway braces with this? Also, is it a problem for the OSB to be in our basement which, although we will have a climate control system etc, is still more humid than other areas? We were thinking of going with moisture resistant drywall as a precaution.

Sway braces - I don't know a lot about sway braces and have been looking at a variety from different companies. Questions:

The sway braces attach to the joist at the outer leaf and then we need to attach the outer leaf to the inner leaf using isolation brackets?

At the wall that has an inner leaf of drywall and then the outer leaf is our existing foundation wall - can we attach the inner leaf to the joists using sway braces? This is the wall that carries our custom laminated windows - so this wall is more top heavy than any others...Also, attaching to the joist would interfere with our firestopping. Is this type of sway brace good for that wall http://www.mason-industries.com/masonin ... N=98880182 Could we attach it to the stripping for our rigid insulation? Yikes...Our existing foundation wall is irregular so I can imagine that the furring will be in excess of 1 -1/2" inches in some places. Therefor the new studs will not be within the dimensional tolerance of the brace...

Are some sway braces more likely to "short circuit" during installation than others? I have found:

http://www.soundproofingcompany.com/sou ... ib-3-clip/

or the WIC sway brace from Mason Industries.

How are these in comparison?

Also, these both require that my new wall be within 1-1/2" of a joist. Not all of our new walls are this close - the two that run parallel to the joists do not. Do we need to add joists - or put some blocking between the joists to bridge and fasten the sway brace to?

Or - can we use an isolation bracket like http://www.soundproofingcompany.com/sou ... tion-clip/ to tie the two leaves together and NOT attach either the inner or outer leaves to the joists using sway braces?

So much to learn about! Daunting and exciting all at the same time. Thank you for your help!

Soundman2020 wrote:

I guess I am wondering if a leaf has to be "air tight" to function as a leaf.

No, as long as there is an air gap between it and the next leaf, then it is a leaf. This is a very interesting read about how that actually works in practice:
http://forum.studiotips.com/viewtopic.php?t=1198

I wouldn't place my career on that empirical data that led to that post. One uncoupled hard boundary versus a coupled two sided interior wall will produce a different signature.