Walls going up in new HT tomorrow, need a quick answer

Discussion in 'Home Theater Projects' started by PaulDA, Aug 15, 2004.

  1. PaulDA

    PaulDA Cinematographer

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    I have the opportunity to add resilient channel to my walls to add to the soundproofing when construction begins tomorrow. Will it make enough extra difference in STC rating to make reworking door frames and outlet boxes and other misc. things or should I content myself with the insulation that I'll be putting in? For space/money reasons, I'm merely opening the existing walls and filling them in, as the original double wall plan is no longer an option at this time.
     
  2. Rutgar

    Rutgar Second Unit

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    It's my understanding, that the main reason for R/C is for acoustical reasons, not sound proofing. R/C will help in your Bass region, and will pay off in the overall sound quality of your finished room. However, you have to know what you're doing when installing. You must be careful not to "short out" the channel, when hanging the sheetrock on it. And you have to careful to not let the sheetrock touch the foor, ceiling, or adjoining walls. On a positive note, you only really need R/C on any single opposing wall, in order to get the benifit. In other words, you only need it on say, the back wall, the ceiling, and the right wall. Not the floor, the front wall, and left wall (if you get my meaning). It's also best to "double layer" the sheetrock on the R/C with a "mastic" layer in-between the two sheets of sheetrock. A good book to get more details on all of this is:

    Premium Home Theater Design & Construction by Earl Geddes
     
  3. Tom Kay

    Tom Kay Stunt Coordinator

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    Hi Paul;

    It's my understanding that almost ALL of the reason for using RC is to attenuate sound transmission through the walls/ceilings, so I must respectfully disagree with Rutgar on this. I should also point out, that since I am only in the process of doing this, and have not yet experienced the full benefits of using RC, I cannot be called an "expert."

    However, I did research as much as possible for about a year on the use of RC, including reading a series of acoustic and sound transmission tests done where I work, at the National Research Council of Canada. I'm in Aerospace, but the beauty of working here is that there are several departments, and the guys share non-proprietary info pretty willingly. I am looking at a Lab Report, written by A.C.C. Warnock, called "The Soundproof Basement" (written when?, not sure) and it shows lots of pics of resilient channel, insulation, drywall, ducts, light fixtures etc. It gives STC ratings, for various arrangements, and I am using Roxul "Safe 'n Sound" insulation, because of its fire rating and high density, in the cavities of my walls and ceiling.

    With one layer of drwall, resilient channel, plus fiberglass batting (not as good as Roxul) the STC is 46. That increases to 50 if you add a second layer of drywall, which I am choosing not to do. Also, I have used 5/8ths drywall, which seems to be much stiffer, heavier and should help reduce sound transmitting through the walls.

    I think the whole idea of RC, is that it "decouples" or effectively almost disconnects the drywall from the framework behind it, and therefore, really acts as a disconnect for the sound. It's not perfect, as those low frequency sounds have a mind of their own, but it kills a lot of the sound right at the drywall/airgap junction. The dense Roxul with its million scrambled pathways for the sound to travel through, ends up trapping/absorbing the sound that make sit through the drywall.

    Call the tech support at the Roxul company. It'll be on their website. The figures they gave me were better than the figures I have on this NRC Lab Report, and this seems right, since their insulation is better.

    Rutgar is correct in saying "You must be careful not to "short out" the channel, when hanging the sheetrock on it. And you have to careful to not let the sheetrock touch the foor, ceiling, or adjoining walls." In other words, don't screw through the drywall, into the RC, and then into ANYTHING AT ALL, or you've then grounded into framework, providing an easy pathway for sound vibration (which kills the effectiveness). An entire wall of drywall hung on RC, should have a sort of springyness to it. You can actually push it in slightly. Remember to mount the RC horizontally on yor walls, with the opening UP, so that when the weight of drywall hangs on it, it causes the RC to open up slightly further (creating a bigger gap between the drywall and the stud framing). I did some tests, and if you use fine drywall screws into the soft flimsy RC, it threads grabs very well (wasn't sure if it would).

    I think though, that this is not actual acoustic "treatment," but in fact acoustic blockage, so to be effective, you need it on all walls/ceilings, so that you don't provide any one easy transmission path for the sound. That's the ideal, and even with this knowledge, I am choosing to do one outer basement wall without RC, just cause it's easier on that particular wall.

    So, that's what I THINK I know. No direspect to Rutgar, as we're all trying to assist.

    Cheers, Tom Kay, Ottawa.
    Hope this helps.
     
  4. Rutgar

    Rutgar Second Unit

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    I think we both agree that R/C is a good thing. And, I never said that it didn't have "some" sound-proofing benefit. My point is that the more important benefit of R/C is the Bass Trapping effect it has on low frequencies, since low frequencies are the most difficult thing to tame in an audio environment. If all you're after is soundproofing, then there are more effective techniques, such as "Staggard Studs".
     
  5. Colin Goddard

    Colin Goddard Stunt Coordinator

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    PaulDa,

    Just go ahead and do it!!! This is a one time opportunity to treat your stud walls before your drywall goes up. And if you don't, you will ALWAYS be wondering, " I wonder how much of a difference it would have made with my HT room if I had of used that rc channel. The electricans will just have to use deeper plaster rings and you door and window jambs will have to be 1/2 inch wider in that room only!! We completed a large church recently and we used rc1 channel to help isolate sound in certain rooms. This was all done within the architects specs, and this was a 4 million dollar church. Go for it!!

    Colin
     
  6. Wayne A. Pflughaupt

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    Great info, Tom. I’m filing it for future reference. [​IMG]

    Rutgar, beautiful website, stunning theater! Want to show it off the next time I’m in Dallas? [​IMG]

    Regards,
    Wayne A. Pflughaupt
     
  7. Rutgar

    Rutgar Second Unit

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    Thanks. No problem, e-mail me. One thing though, the room's going to be out of commission for a few weeks, because I'm sending the Processor in to Classe' for an upgrade. I have no idea how long that will take.
     
  8. PaulDA

    PaulDA Cinematographer

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    Well, when we opened the existing wall to fill it with insulation we found it was less thick than we'd assumed (part of it is under a stairwell and was only 2 1/2 inches thick inside the drywall). We decided to insulate the existing wall, frame a parallel wall one inch out, fill it with insulation and wall it off with drywall. According to the manual I consulted, that should give me an STC rating of 57 or so, and that's well within my needs. Thanks for all the suggestions and I will keep them in reference should I get the chance to build a room from scratch (either here or in a future house).
     
  9. JohnBrianW.

    JohnBrianW. Stunt Coordinator

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    This weekend I'm going to put up the last wall of my listening room, which is an interior wall. I came on here to confirm my idea of doing a staggered studded wall and started to read about R/C and a question came to mind from the responses above. Because the wall "floats and has some movement, what does this do to the seams? I can't see how the mudding won't crack?

    The other has to do with staggered studding. I'm still looking through the posts, but assume you use 2X6 for the header and footer? How does this affect the framing of doors? My idea is to put in a double French door, but the framing for doors is usually designed for a 2X4 wall isn't it?

    Scott
     
  10. Rutgar

    Rutgar Second Unit

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  11. Tom Kay

    Tom Kay Stunt Coordinator

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    Hi John

    I wondered too, about how to do the seams in the drywall. I just did my first couple of resilient channel-mounted drywall walls this past weekend. I hadn't read up about using caulking for the seams, and I just assumed I'd have to find a way to make the seams rigid. So I mounted backing plates on every edge, glued to the back of the drywall. I used 3/8ths plywood, and made sure that it touched nothing on the rear surface of the plywood backing plates. The plates are strategically located strips of wood, not a full backing plate the size of the drywall sheet. I have not taped or mudded yet.

    I didn't read about this anywhere. I just assumed this would be an appropriate way to do seams. So I would not guarantee its performance, but I can say that none of my drywall, resilient channel or backing plates have been errantly "grounded" to any wall framework thus far. In effect, it's like I have one big piece of drywall the size of my entire wall, all mounted on RC.

    Here's a possible error source on my part. I didn't know how many horizontal strips of RC to use. My wall is 7 feet high. (I wish I'd read the artical that Rutgar pointed out). I guess 3 horizontal strips would have been enough, but I used 5. The top and bottom ones were about 6 inches from the top and bottom of the drywall, so I could add some glued backing plate and use the this to secure crown molding, and baseboard trim. I also added a backing plate to the middle of the drywall, so I can secure a chair rail around the middle height of my room.

    I then noticed that the walls were not as springy as I had anticipated, so I'll use only 4 horizontal strips for my front HT wall. With all of the added weight, maybe this isn't a bad thing, plus that 5/8ths drywall is heavy. Still, even though RC feels flimsy, I'll bet that when it's all screwed up tight, the wall feels more secure and firm than you'd have guessed. I don't think having one or two extra strips of RC will hurt that much, but hey, I'll find out.

    I am curious to see how my backing plate reinforced seams work. I'll report when I know.

    Cheers, Tom Kay.
     

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