Reason for double studded walls in your float center – DSP 07

What the heck are double stud walls and why would I need them?

Graham and Ashkahn talk about this and how a high level of soundproofing and construction design can make the difference between a perfectly quiet float, and one where you can hear the person chanting and doing yoga in the room next to you and trucks rumbling by outside.

When it comes to float centers, what’s inside the walls is what makes the experiences outside them so special.

Beyond Air Gaps — Build Storage to Increase Soundproofing in Your Center

FTS Construction Packet

Listen to Just the Audio

Transcription of this episode… (in case you prefer reading)

Graham: Today’s question, from one of our listeners is, What the heck are double-stud walls and why should I use them?

Ashkahn: Oh, okay. I was hoping we’d get away with that, talking about why they’re used at all, but they had to sneak that in there, huh?

Graham: Yeah, because the “what” is really the easy part of the question.

Ashkahn: Yeah, it’s two sets of studs in a wall.

Graham: I don’t know actually how to describe it much better than that, except you have actually two sets of base studs or the base plates, two top plates, and you have two rows of studs that make up your wall with an air gap in between them, which can usually be anything from an inch up to a foot or so.

Ashkahn: It’s basically like two walls, like you just have a wall right next to another wall, is what a double-stud wall is.

Graham: As opposed to a single set of studs with the walling material on both sides of that, which would be a single-stud wall.

Ashkahn: Why you use them almost feels like the better part to start with, because they sound really weird without knowing why you’d ever build something like that.

Graham: That takes twice as many materials, twice as much labor.

Ashkahn: Like, “I already have a wall. Why would I build another wall?”

Graham: The reason that you want them is that they help a lot with soundproofing. One of the core parts of soundproofing your float center, and any room that you want to soundproof really, is to have some kind of air gap built into the wall. You can accomplish that through a couple different means.

You can also have a clip and channel system, where you actually attach these clips to a single-stud wall and have some channels you run through there and then put your drywall material onto those channels, and that creates an air gap as well. I won’t go into that too much. You can look it up if you want to see diagrams. It should make a lot more sense than listening to my voice over the air.

For the double-stud wall, it’s actually much more understandable. Those two studs are not connected, and so once you have the sound waves hitting one side of the wall, the material on one side, they’re not just transmitted directly through the studs to the other side of the wall and then out. They hit that wall material and then they have to go through this air gap before they hit the material on the other side and then come out. It turns out that just that transition between solid, air, and back to solid again, is what accomplishes a huge amount of your soundproofing in your rooms.

Ashkahn: The more of an air gap you have in between there, the better it tends to do with soundproofing, so as the sound travels and hits that wall, it gets into that air space in between and it’s basically resonating through that air space. What happens is when you set those two walls further apart from each other, you’re making that air space larger, and as a result you’re making the frequency that it resonates at, which is the most likely or the easiest frequency of sound that can travel through that medium.

You’re making that go lower and lower. The lower you can get it, the better it tends to be for human ears. Our human ears have more trouble detecting it when it’s in those lower ranges than the higher ranges around the human voice and stuff like that. Having that larger sound gap tends to be better soundproofing.

Graham: Similarly with that, because that frequency is specific, we’ve also heard, although we haven’t played around with it much ourselves, that actually skewing the walls a little bit so they’re offset on an angle by a few inches so they’re not totally straight will further increase the cost of your construction, first of all, because not only are you building two sets of studs, now you have to do some crazy scribing on the ceilings because your walls aren’t actually parallel to each other.

Theoretically, that will actually even cut down on that resonant frequency that’s bouncing around in there, because you don’t have one flat plane in front of another, and cut down on the reverberation bouncing back and forth between them as well. That’s something else that can help with that effect. Another question that the listener didn’t ask but which I’d like to ask for them is if double studs are awesome, why not use triple studs or even a quadruple-stud setup?

It turns out in the case of having three sets of studs or sometimes more commonly two studs but you’ve covered both sides of one stud with wall material and both sides of the other stud with wall materials, now you have four times as many or twice as many sheets of walling up there.

There’s names for those. The amount of walls that you have up is called the leaves, is the actual sheets that you have. If, in a double-stud setup, only the outside of either of your studs is covered, that’s two leaves that you have there. If you were to cover, then, the inside as well, that makes it four leaves. Or if you had three sets of studs and only one side of each of them, that would be a triple-leaf system.

Ashkahn: These are actually generally regarded as worse soundproofing than what you could do with the same material were you to just have two leaves, so if you’re using the same amount of lumber and the same amount of drywall and all of that, it’s actually best to just have a solid chunk on the outsides and a big air gap in the middle.

That goes back to that resonant frequency of the air. As soon as you’re cutting that giant air gap into two small air gaps, because now you have a leaf in the middle or a wall in the middle, now you’re making two smaller bodies of air that can, again, resonate at those higher frequencies rather than the lower ones.

For the same cost, for the same amount of materials, and for the same space that it takes up, you generally are best off with as much material on the outsides as possible and as big of an air gap in the inside as possible.

Graham: Yep. To the point where you can use the exact same amount of material and just by switching two of the leaves to the inside of the wall as opposed to all of them being on the outside, you can cut the soundproofing in a quarter, so you’re now being a quarter as effective in your soundproofing just by rearranging the material instead of having that single big air gap.

Ashkahn: The last part of all this is that you want to reduce the amount of resonance once the sound is inside those walls as much as possible, too. That’s where this soundproofing insulation comes from.

While it seems like soundproofing insulation is something that’s going to stop sound from going through, it’s actually much more there to dampen sound on the inside of walls so when sound gets in, instead of bouncing back and forth wildly between your two sets of drywall, there’s sound like rockwool type of material specifically sound-absorbent insulation in there that is meant to dampen it and catch it so that you don’t create this kind of drum-like resonant body inside of your walls. Or as I like to say, guitar-like resonant frequency inside the walls.

Graham: That’s why people use double-stud walls.

Ashkahn: Yeah, good. Solid.

Graham: You think?

Ashkahn: Double solid.

Graham: Thanks for tuning in. We’ll see you tomorrow.

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