Single layer drywall

Discussion in 'Home Theater Projects' started by Roy Brooks, Dec 6, 2004.

  1. Roy Brooks

    Roy Brooks Agent

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    I'm getting ready to drywall the basement. The hometheater will be a single layer drywall with 5/8 ceiling and 1/2 walls. I was thinking of adding resilence channel to the walls and ceilings. Is there anything else I could do to decrease sound travelling? I heard of people using acoustic caulk, where is this used? between every edge or just top and bottom? doesn't it get squeezed out and make a mess during the mudding? Iwas going to use drywall for the soffits are there advatages in using mdf? and if so what size mdf? I have a cold air return that runs the length of the room 8" from the wall then another 8" space and a second heating duct. I was going to put an 8" strip of drywall in this area before I box the ducts in to reduce sound as there are pot lights going in one of the 8" spaces. What could be used aroungd the ducts to further reduce sound travelling?
    Thanks Roy Brooks
     
  2. Wayne A. Pflughaupt

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    Roy,

    There are three keys to effective soundproofing:
    • Dense partitions, best accomplished in the home by doubling 5/8” sheetrock, the use of solid-core exterior doors, etc.
    • Dead air space between walls (or ceiling/upstairs floor) that are physically separated or de-coupled.
    • An airtight room.
    The further you move from these elements, the less you can expect in the way of effectively minimizing sound transference.

    From what I gather from your post, your plans don’t include any of these elements, so I think it’s safe to say that you can expect the results to be minimal at best.

    Regards,
    Wayne A. Pflughaupt
     
  3. Roy Brooks

    Roy Brooks Agent

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    The theater is in the basement and has 3 outside block walls, so for these walls there is a 3.5" wood stud wall insulated with heavy mineral wool insulation and 1/2 to 1" air gap then the block wall and the dirt. The forth wall is the interior wall is a staggered stud wall to be insulated and then either add drywall or resilience channel and then the drywall. If I go with 1 sheet of 5/8 drywall that should give a STC rating of 48 if I add 2 sheets of 5/8 drywall it should bring it too an STC of 59. Would the 2 sheets of drywall provide a bigger STC rating than one 5/8 sheet with the drywall decoupled using the resilience channel? The second part becomes if you have walls that have an high STC rating unless the ceiling also has a high rating are you wasting the money for extra drywall? What kind of increase in the STC rating will adding the RC provide? The doors to the room will be external steel doors with thresholds.
     
  4. SteveLeach

    SteveLeach Stunt Coordinator

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    This site has plenty of good information on soundproofing a room. It is a commercial site. I have no opinion on the company, as I neather work for them nor have I purchased from them. http://www.soundproofing.org/
     
  5. HowY

    HowY Extra

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    Thought about soundboard...

    Works way better than hat track...

    I generally put up soundboard then
    hat track then the rock. Sounds
    like your suituation.

    5/8" all 'round

    Staggered stud wall is the best solution

    Soundboard & roc for your soffit work
    MDF is weighty stuff!

    Good Luck!
     
  6. Tom Kay

    Tom Kay Stunt Coordinator

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    Hi Roy

    I have a couple of info sources that you might be interested in, and I'll share them here. First, I work at the National Research Council of Canada, although in an Aerospace lab, not acoustics, but we do have acoustic labs who love to help with questions. Second, I just called Paul Warren, tech department of Roxul Insulation (905) 875-9318. He has stats about insulation/isolation methods.

    From NRC I have a paper published by some guy named A.C.C. Warnock (never met him, but I'm sure he's a smart guy). His paper is "The Soundproof Basement" and he talks about resilient channel, layers of drywall, batting, ducting etc.

    His figures of STC are quite close to the figures given to me by Roxul. So I'll give you some numbers from the Roxul study:

    Using one layer of 5/8" drywall, NO resilient channel, and 3.5 " of batting, this gives an STC of 36. This means 36 db of attenuation through a wall.

    Using resilient channel with the above setup gives an STC of 45. Add a second layer of 5/8" drywall, and the STC becomes 51. This assumes 16" centred wood studs. If you have 24" centred wood studs, the STC rating is 54, I think because the "coupling" of the drywall to the wood studs is reduced (fewer connection points for a given wall area).

    Mr. Warren also mentioned that 70 percent of the STC rating comes from how well you make your structure, and 30 percent comes from the batting. Where Roxul helps, is that it's denser than fiberglass, (since it's made out of crushed rock and slag) so it does a somewhat better job of attenuating the low frequencies. But very little can really kill those booming bass sounds.

    He also mentioned that you need an air gap between the batting surface and the drywall, so never jam the wall or ceiling cavity full of batting. And he said that using 3.5 inches of batting in the ceiling gives almost the same STC rating as filling the full joist cavity, so there's very little acoustic benefit to using a second layer of 3.5 inch batting to fill up the joists.

    So, in summary, you've asked lots of questions, and I know I haven't answered them all, but it looks like the right thing to do, to use resilient channel. I used it in my basement, and it was not a pain in the butt, like I thought it would be. Just use fine screws and don't screw through the drywall into any framework, or you've "grounded out" your floating wall.

    Also, I have not finished my HT to the point where I can say that there's great benefit to all of this work, but I really think I'm on the right path, using RC, dense insulation and the 5/8" drywall. I'm only using one layer, but some might choose 2.

    I hope this answers some of your concerns.

    Tom Kay, Ottawa.
     
  7. Ron-P

    Ron-P Producer

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    For what it's worth, I used two layers on my interior walls. First layer was 1/2" and the second was 5/8". The walls were then stuffed with R-13. The exterior of the theater is 1/2" drywall finished with 5/8" OSB.
     
  8. Roy Brooks

    Roy Brooks Agent

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    I notice that the roxul safe and sound product is 3" thick, not the usual 3.5" for a 2 by4 wall this must be for a 1/2" air gap to deaden sound further. I didn't know you could use 2 layers of drywall on resilience channel, I'm concerned that it would rip the screws out of the studs. I guess you have to do some great measuring to make sure you don't ground out the wall. How are the corners handled with the RC? if the wall and ceiling should move independantly have do you mud and tape the corners? wouldn't it crack the mud if the two move? Also for a staggered wall 6" thick (3 5/8 + 1 5/8)would you just use the 3" roxul safe and sound and have a 2 1/2" air gap?
     
  9. Tom Kay

    Tom Kay Stunt Coordinator

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    Hi Roy

    I plan to handle the corners by keeping them separated by a slight gap. No tape and mud, and I am pretty sure you're not suppose to tape and mud adjoining surfaces.

    I'll fill in these 1/4" gaps with anything from soft foam, acoustic caulking etc, but I'll also use some small trim to cover the gap, make it look planned. I have never used acoustic caulk, but I've heard it's messy, so that's also a good reason for covering the whole thing with trim. I have heard many times, seal it air tight. If air can leak out, so can sound !!

    I would mount the trim on one surface and have it hovering above the other surface by a very small gap, so that again, the two walls are truly separate. I have even thought of having soft rubber tubing as a gasket, lightly jammed in place under the trim, squished against the other wall.

    The Roxul tech said that adding more batting has surprisingly little impact on sound attenuation, something like 1 STC per inch of thickness. So, that's why 3" of Roxul Safe n Sound should be enough, and why I will not waste money filling my ceiling cavities. If you have room, you might choose Roxul "Flexbatt" which is something like 5.25" thick, but then again, the Safe n Sound should be fine.

    I've mentioned Roxul so much that you must think I own shares, but it just seems to have so many advantages over fiberglass. It withstands double the temperature, it works even if wet, and won't rot or mildew (ever seen yucky black fiberglass??). It's easy to cut. I wish I owned shares.

    I wondered too if 2 layers of heavy 5/8" drywall on the ceiling would pull out of the screws, or out of the joists. It seems to not do this, and I have seen it mounted like this in one of our building research labs. That's one of the questions I asked. Still, I'll just be using one layer of 5/8" drywall in my ceiling when I do it. My walls are done, just the ceiling to go.

    If you're in the mood, call the Roxul company. Maybe they have other good nuggets.

    Have fun. I certainly am. Drywall dust, hack, hack.

    Tom.
     
  10. Roy Brooks

    Roy Brooks Agent

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    I used roxul products in both the house and cottage so I will try the safe and sound. The corners could be trimmed out later with maybe a nice cording from the local fabric store, maybe hot glued to one surface.
     
  11. Eric_nord

    Eric_nord Auditioning

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