Ceiling soundproofing (SPC 3 or 2) - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 17 Old 09-09-2018, 07:34 AM - Thread Starter
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Ceiling soundproofing (SPC 3 or 2)

I'm getting close to placing my drywall order. I've been thinking I was going to take the SPC solution 3 all along where you place 2 layers of drywall to the subfloor. I'm curious how many of you do that or do you just do the level 2 (hat channel and double drywall and insulation).
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post #2 of 17 Old 09-09-2018, 08:55 AM
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If you have a hard surface floor above, adding the damped mass directly to the underside of the subfloor works well to cut the sounds of people and pets moving above. I’ve done it several places.
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post #3 of 17 Old 09-09-2018, 09:09 AM - Thread Starter
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Thanks, i already have the Green Glue to do it. We have a carpeted floor above currently but that is only because the builder wanted to charge an insane amount to put in junk hardwood throughout. It will eventually be hardwood. I have 2 young kids so the extra effort I'm sure will be worth it to me.
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post #4 of 17 Old 09-09-2018, 06:35 PM
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Be careful of screw length, you won’t see them sticking up in carpet, but you will find them with your feet. One guy had his contractor do it and a helper had pocket full of the wrong length screws. You can order one inch drywall screws on Amazon.
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post #5 of 17 Old 09-09-2018, 08:07 PM
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It is well worth putting drywall in the joist cavities. The drywall itself is pretty inexpensive and it is relatively easy to do. The cost of the Green Glue adds up, but it is well worth it. It is much better to apply mass to the bottom of the floor above to minimize footfall noises that to try to block it out once the vibration gets in the the structure.

The measurements don't need to be exact. Measure each cavity as you go along and cut the drywall around 1/4" less, giving you 1/8" or so on either side. I found that it was easiest to use 4' long sections of drywall, cutting "strips" out of the 4x8 sheets of drywall. Small gaps on the sides won't matter, the goal is mass. The most difficult parts are cutting off any screws or nails that are hanging down from above, and working around ductwork. Neither is really "difficult", "time consuming" would be a more accurate description.
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Last edited by DaveClement; 09-10-2018 at 07:18 AM. Reason: typo
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post #6 of 17 Old 09-09-2018, 09:12 PM
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One thing I’ve seen guys do is cut 8ft long strips which is a lot harder than 4ft and offers NO advantage in this application. 8ft strips take two people and two ladders, you can put up 4 ft pieces by yourself. Overlap the seams.
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post #7 of 17 Old 09-10-2018, 07:08 AM - Thread Starter
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Thanks guys, I have 1 really tricky joist, but the others should be easy to deal with. I'm glad you mentioned 4' sections, I was thinking it the less seams the better.
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post #8 of 17 Old 09-10-2018, 07:22 AM
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Originally Posted by elitemikes View Post
Thanks guys, I have 1 really tricky joist, but the others should be easy to deal with. I'm glad you mentioned 4' sections, I was thinking it the less seams the better.
For the "tricky" joist cavity, it is OK to cut the drywall in smaller sections to fit around obstructions. That makes it a lot easier to get the sizing right and to move around the obstructions. There are no extra points for neatness, only for mass.
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post #9 of 17 Old 09-10-2018, 07:57 AM
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Be sure to get a drywall T square to make quick work of cutting the strips. measure each cavity don’t assume that that they are all the same.
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post #10 of 17 Old 09-11-2018, 10:13 AM
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Great thread, hadn't thought about using 4' sections for ease of installation.

Is this worth doing to reduce sound transfer the other way? Up through the floor from below, not just for footstep sound going down?
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post #11 of 17 Old 09-11-2018, 10:33 AM - Thread Starter
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Quote:
Originally Posted by Thurston9 View Post
Great thread, hadn't thought about using 4' sections for ease of installation.

Is this worth doing to reduce sound transfer the other way? Up through the floor from below, not just for footstep sound going down?

I'm certainly not the expert, but according to Soundproofing company, it adds 10pts to the rating
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post #12 of 17 Old 09-11-2018, 10:44 AM
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Quote:
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Great thread, hadn't thought about using 4' sections for ease of installation.

Is this worth doing to reduce sound transfer the other way? Up through the floor from below, not just for footstep sound going down?
I believe it is not worth doing for sound travelling in the other direction. It would be overkill for not much gain. It is targeting footfall vibration frequencies propagating through the floor structure. The sound leaving the theater is better treated using other methods.
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post #13 of 17 Old 09-11-2018, 10:45 AM
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I'm certainly not the expert, but according to Soundproofing company, it adds 10pts to the rating
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Originally Posted by impreza276 View Post
I believe it is not worth doing for sound travelling in the other direction. It would be overkill for not much gain. It is targeting footfall vibration frequencies propagating through the floor structure. The sound leaving the theater is better treated using other methods.
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post #14 of 17 Old 09-11-2018, 10:49 AM
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Yes, adding the extra mass will definitely provide additional sound isolation in both directions. The caveat is that placing the mass between the joists isn't the only place that you can put it. For example, instead of adding one or two layers inside the joist cavities, you could add additional layers to the ceiling inside the room that you are trying to "soundproof". This would probably be a lot easier since you can put up whole 4x8 (or 4x12) sheets all at once without any tedious measuring or cutting. Plus you wouldn't have to deal with nails and screws coming through from above, working around pipes and ducts, etc. There are downsides to this. One is the loss of ceiling height. Adding two more layers inside the room will eat up an extra 1-1/4". That isn't a lot in a high ceiling, but it certainly is in a ceiling with low clearance. You would also need to deal with the additional weight, which is more than clips and channel can handle in a standard configuration.
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post #15 of 17 Old 09-11-2018, 10:51 AM
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Quote:
Originally Posted by Thurston9 View Post
You are much better off using three layers of drywall rather than the between-joists drywall if you want to reduce the sound leaving the theater. Also STC ratings are a basic measure that do not tell us nearly enough of what we need to know.
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post #16 of 17 Old 11-24-2018, 05:46 AM - Thread Starter
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I'm getting ready to start this task. I'll be purchasing a few sheets of drywall at a time and cutting them in half at the local big box since since I'm not ready for the big order. I have to do a few of the cavities before I can put up some cross members so i can mount my clips.


Is it worth cracking open a green glue and praying it doesn't go bad if I'm going to be doing some small sections?I'm making good progress marching towards drywall. I'm hoping to get my big order around the new year.



I need to get ALL framing done before my father in law comes back up, he doesn't understand the point of not connecting the inner walls to the outer in my floating sections. I have my av nook/niche in place and need to get some IB3 clips. His thought is it's so small, why not just connect it to the walls that are getting the clips but don't use the clips.... He thinks it's all overkill, but I came this far I'm not about to screw it up. I'll go to work and come home to him making changes. He's a retired shop teacher that became a contractor so regular building techniques make sense to him, but none of this does.
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post #17 of 17 Old 11-24-2018, 10:09 AM
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lock the door to the basement when you are at work.
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