Soundproofing master thread - Page 18 - AVS Forum
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post #511 of 519 Old 07-16-2014, 04:43 AM
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Originally Posted by SteveS78 View Post
How low would my ceiling be lowered if I choose to decouple it from the joists?
There are several ways to do this... if you use Sound Clips & Hat Channel... I think there are two ways...

The first way is about 2 1/8" lower.. you attach clips directly to sub-floor joist, and run hat channel perpendicular.

The second way, is more labor intensive, but you could likely do for about 1" lower... you would have to install 2x4 cross bracing 'up' in between the joists with teh bottom edge of the cross-bracing about 1" HIGHER than the bottom edge of the Joist. Then, when you install the 'clip', the 1 1/8" deep clip, only 1/8" extends beyond the joist bottom. Then it is just the 7/8" hat channel depth.

I have seen other applications where people install entire new Joists in between their existing joist. This could likely be as little as 1/4" lower, but requires somwhere to rest the joists on (i.e., if building room within room, you would have the 'new walls', which the joist could rest on). If I am not mistaken, the guy who started this thread may be doing this method - you might take a look at his build (Ganroth, I think it is called the Phoenix Build).
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post #512 of 519 Old 07-16-2014, 05:47 AM
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Thanks for the info. Does it make a difference as to what is above my basement in terms of making this decision? Right above where the screen and speakers will be is our family/great room that has a cathedral ceiling. Nothing is above that. The bedrooms are above the unfinished area of the basement with a floor in between of course. The floor of the family/great room is carpet and the kitchen is also directly above part of the finished area, just a little bit to the right of where the screen and speakers will be. It has a plastic laminate floor. Hopefully those surfaces (carpet and laminate) will help a little bit with sound.

I just looked last night, the pink R13 Owens Corning insulation is in the walls and they have stuffed that same insulation VERY thickly (10 inches) between the joists. It looks very sufficient. Its so thick its almost busting out in a few spots. Haha. Also, he just insulated the ceiling area above the speakers and screen. The area to the right of that is going to be a play area for the kids (just an open area), and I have chosen not to insulate that. I am sure some sound would escape there. We also have a stairway that already has a finished drywalled ceiling with the door to the upstairs. I am sure some sound would escape there too.

Last edited by SteveS78; 07-16-2014 at 05:50 AM.
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post #513 of 519 Old 07-16-2014, 09:54 AM
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Quote:
Originally Posted by SteveS78 View Post
How low would my ceiling be lowered if I choose to decouple it from the joists?
Depends on how you do it. If you run new decoupled joists from the side walls, you can manage fractions of an inch depending on how accurate/brave you are with the measurements. Myself I lost about an inch, but I also went for more drywall layers than originally.

Under construction: the Larch theater
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post #514 of 519 Old 07-17-2014, 07:01 AM
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Originally Posted by kmhvball View Post
There are several ways to do this... if you use Sound Clips & Hat Channel... I think there are two ways...

The first way is about 2 1/8" lower.. you attach clips directly to sub-floor joist, and run hat channel perpendicular.

The second way, is more labor intensive, but you could likely do for about 1" lower... you would have to install 2x4 cross bracing 'up' in between the joists with teh bottom edge of the cross-bracing about 1" HIGHER than the bottom edge of the Joist. Then, when you install the 'clip', the 1 1/8" deep clip, only 1/8" extends beyond the joist bottom. Then it is just the 7/8" hat channel depth.

I have seen other applications where people install entire new Joists in between their existing joist. This could likely be as little as 1/4" lower, but requires somwhere to rest the joists on (i.e., if building room within room, you would have the 'new walls', which the joist could rest on). If I am not mistaken, the guy who started this thread may be doing this method - you might take a look at his build (Granroth, I think it is called the Phoenix Build).
I must have been sleepy... the Clip + Hat Channel is 1 1/8" drop if installed directly on floor joist.

Doing the Cross Bracing, you run the channel parallel to floor joist, and the recommended gap is 1/2". So, you 'gain' 5/8" for that extra labor/ time & material. I think doing a room within a room, could likely even bring that 1/2" lower.
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post #515 of 519 Old 07-17-2014, 03:05 PM
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Originally Posted by SteveS78 View Post
How low would my ceiling be lowered if I choose to decouple it from the joists?
If you decouple your ceiling with hat channel and clips and use double dry wall with green glue your ceiling will be lowered by 2".
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post #516 of 519 Old 07-20-2014, 10:11 AM
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Originally Posted by Nightlord View Post
Depends on how you do it. If you run new decoupled joists from the side walls, you can manage fractions of an inch depending on how accurate/brave you are with the measurements. Myself I lost about an inch, but I also went for more drywall layers than originally.
Isn't each layer of fire-rated drywall 5/8 inch thick? If you had two layers, you'd be at 1-1/4 inches, and that's with no clearance from the ceiling. Add half an inch for clearance, and you're at about 2 inches lost.

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post #517 of 519 Old 07-20-2014, 10:46 AM - Thread Starter
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Okay, let's start with a "typical" ceiling consisting of one sheet of 1/2" drywall directly screwed or nailed into the joists. That's our baseline.

Let's now replace that 1/2" drywall with 5/8" Type X drywall. Net loss is 1/8" and it gives us marginally better soundproofing.

Let's add another sheet of 5/8" Type X drywall. Now we have Joist + 5/8" DW + 5/8" DW, giving us a net loss of 3/4". The soundproofing is now notably better than the baseline.

Why not add a layer of Green Glue in between the drywall? The thickness of the material shouldn't change in any easily measurable way (save using a micrometer) but the sound reduction will be noticeably better than even the standard double layer.

But now we'll kick it up a notch and decouple, in addition to adding mass. This is where the true bang for the buck kicks in.

The least amount of lost vertical space would be to create floating joists between your existing ones -- but this does assume that you also have floating walls (a "room within a room" construction method). You'll lose around 9" in each dimension for width and length of the room. In theory, you could create your new joists and new walls to be maybe 1/8" below your existing joists. That would give you a net loss of 7/8". That would assume some pretty straight existing joists, though, and that's not been my experience. It's probably safer to assume around 1/4" clearance, which creates a net loss of 1". This will be your close-to-ultimate soundproofing solution (and not just for the ceiling).

You could get a similar amount of lost vertical space by offsetting clips and channels into the existing joists using blocking. See this illustration from the Soundproofing Company:



This gives you roughly identical vertical loss as the floating joist solution. It has very similar soundproofing capabilities to the floating joist solution, albeit costing a bit more and not addressing the walls or flanking.

If all that seems to finicky, then the standard solution is to use 7/8" clips and channels with the two layers of 5/8" Type X drywall (and Green Glue). Net loss there is 1-5/8". It has the same excellent soundproofing abilities as the "blocking" solution, but far easier to install and only giving up a maximum of 5/8" more.
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post #518 of 519 Old 07-20-2014, 10:56 AM
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Originally Posted by ctviggen View Post
Isn't each layer of fire-rated drywall 5/8 inch thick? If you had two layers, you'd be at 1-1/4 inches, and that's with no clearance from the ceiling. Add half an inch for clearance, and you're at about 2 inches lost.
We only have 1/2 inch drywall here (12 or 13mm ) afaik, and I've never heard of it being fire-rated or not. But most of all, I had a layer of wooden beams perpendicular to the joists in the original ceiling that I didn't do now, so I saved a little space.

Under construction: the Larch theater

Last edited by Nightlord; 07-20-2014 at 11:25 AM.
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post #519 of 519 Old 07-27-2014, 04:46 AM
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Originally Posted by Nightlord View Post
We only have 1/2 inch drywall here (12 or 13mm ) afaik, and I've never heard of it being fire-rated or not. But most of all, I had a layer of wooden beams perpendicular to the joists in the original ceiling that I didn't do now, so I saved a little space.
Sounds good. This is fire rated drywall:

Article about fire rated drywall

It's commonly used for sound transmission since it's heavier than normal 1/2 inch drywall. The 1/2 inch is about 1.6 pounds/ft^2 (square foot) and the 5/8 inch is 2.2 pounds/ft^2. A 4x8 foot sheet of 1/2 inch is about 51 pounds while the 5/8 inch is 70 pounds. I was used to carrying the fire rated, 5/8 inch stuff around, then picked up a 1/2 inch sheet and couldn't believe how light it was.

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