help with adjacent wall decoupling

[cyeazel]

How's it going. This is my first post so forgive me if my question is a little unclear. Anyway, I have a room with with both hollow concrete walls and 2x4 stud walls. I want to put up new frames in front of the studded walls making them double partions but I'm not sure of the best way to decouple them from the concrete walls. I want to avoid the 3 leaf system with the concrete walls so I plan to just add layers on them. What is a good way to make sure that studded frames remain decoupled enough from the concrete walls so as not to short circuit or decrease TL from them. If this isn't enough information, let me know.

[the dreamer]

.....but I'm not sure of the best way to decouple them from the concrete walls.
What is a good way to make sure that studded frames remain decoupled enough from the concrete walls so as not to short circuit or decrease TL from them.

Do the studs have hard contact to the concrete wall?

It seems that you already have a 3 leaf system, so you're right with adding mass.

[cyeazel]

Hey. Thanks for the reply. Let me see if I can explain what I mean a little bit better. The existing construction in the room has hollow concrete walls on the north and west sides, and studded walls on the south and east sides. The north(concrete) wall has 2 layers of 5/8" drywall mounted to wood furring channels and the west (concrete)wall has 1 layer of 5/8" drywall mounted directly to the concrete. The south and east walls are studded (2x4 with 1 layer 5/8" drywall on both sides). The studded walls are directly mounted to their adjacent concrete walls. What I want to do is build additional new frames for the studded walls making them double partitions. I can't (or at least shouldn't) build new frames for the concrete walls because I want to avoid the 3 leaf thing, so I plan to just add mass to them. I'm just not sure what the best way is to decouple the newly built studded frames from their adjacent concrete (plus added mass) walls.

Does this make a little more sense?

[the dreamer]

In case you didn't read already:
http://www.johnlsayers.com/phpBB2/viewtopic.php?t=598
Most of what you want to know and a lot more is detailed in this thread.

south and east walls are studded (2x4 with 1 layer 5/8" drywall on both sides). The studded walls are directly mounted to their adjacent concrete walls. What I want to do is build additional new frames for the studded walls making them double partitions.

If I understand you right, the studwalls are already a 2leaf, if you put another studwall in front you end up with a 3leaf sytem. What you could do is to remove 1 side of the wall and build a new studwall (staggered if possible) with several layers on one side only!
How are you going to deal with the ceiling? You have to take every direct and flanking path into account. and then build accordingly.

I'm just not sure what the best way is to decouple the newly built studded frames from their adjacent concrete (plus added mass) walls.

I think you will find the answer in the mentioned thread. What I do not understand is your worrying about the decoupling as your concretewalls are gonna be big flanking pathes anyway. Sure by decoupling you will gain a bit and it would be silly if new build not to decouple but your major problem is the concrete.
Somewhere I read that one person infused expanding foam (hope it's the right word...it's getting real hard when cured) into a hollow concrete wall makin it one leaf. So no 3leaf problem with adding a studwall anymore.

But maybe this is overkill in your case depending on how much isolation you need.
Florian

[cyeazel]

Thanks again for the reply. Yeah, I read thru that link before, although, probably not good enough. I think I'm assuming to much when I post, or should I say, that people will know exactly what I mean from reading my questions. After re-reading both of my posts, I understand that what I thought was way off. Anyway, to make a long story short, I guess a sketch is in order. Hey, out of couriosity, were you in the studiotips.com forum on floating floors? Your name, Dreamer, I think was in there too, or was that someone else?

[the dreamer]

Your name, Dreamer, I think was in there too, or was that someone else?

Yes that's my post. I learned a lot on floors and decoupling in general (thank god...and Eric/Paul...before I started to build). Where would DIYers like you and me end up if there were no such generous people as Eric, Steve, John, Rod and all the others.

[cyeazel]

Yeah, I totally agree. The free help is so nice to have. Hey, quick question. I work for my dad(family busisness) and the rooms I trying to convert to a studio are upstairs here. Anyway, we stock rolls of neoprene rubber and I was wondering if cutting large sheets of this stuff and using it in the studio might help with at least some sound isolation ( obviously it depends on how and where I use it). But it's free, so I don't really need to worry if it works or not because I'm not losing anything either way. Any thoughts?

[the dreamer]

But it's free, so I don't really need to worry if it works or not because I'm not losing anything either way. Any thoughts?

From what I learned this can be a trap if not designed to a resonace frequency lower than your gear is able to transmit. When it resonates within the audible it amplifies.
Eric D explained that EPDM/Neoprene works on deforming, means bulging out when under load. To work properly you have at least to calculate the entire mass wich consists of the floating floor, the walls (on the floor), the ceiling (on the walls...room in room), desk/equippment, etc.
So the deflection under load should be 10-15% for good decoupling. The problem with lightweight floors (wood/MDF, etc.) is, that the liveload (people/gear, etc.) is changing all the time. So this will affect the resonance behaviour of the Mass-Spring-Mass system (the floor-neoprene-subfloor). More mass lowers the resonance which in general is good, but could bottom out your pucks (no decoupling anymore) or decrease the lifespan considerable.
On the other side a heavy concrete floating floor with walls an ceiling on it has enormous mass already and some guys with beers won't change the deadload/liveload ratio so much. This means the resonance frequency wont change as much. For example Paul W can take 2 tons of liveload changing the res. frequ. for only 1 Hz.
If you can make a concrete floating floor (heavy) depends on the structural situation in your building. You might need an engineer for this, otherwise this could be dangerous.

I hope this makes sense as this is recently digested stuff, but you could read that in the studiotips thread you mentioned.
The next thing is: It seems that the lifespan for neoprene is 10 years only!
I wouldn't want to tear down my studio in 10 years.

Florian