New HT walls/acoustics

Discussion in 'Room Acoustics, System Layout & Setup' started by tgoldbeck, May 4, 2012.

  1. tgoldbeck Audiophyte

    tgoldbeck
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    I have a room in our new house designated exclusively for a home theater (my wife got a huge closet in exchange for my home theater), and need some advice on how to set it up. The room is 18’ wide, 28’ long, 8.5’ tall, and is completely underground (beneath the garage). Three walls and the ceiling are poured concrete and one long wall is just framed 2x4’s right now.

    My first question is: do I need to drywall any of the concrete walls/ceiling, or can I cover them as they are with acoustic panels? Also, do I use plywood, drywall, or something else to cover the 2x4 framed wall and other walls? I was planning on using as many acoustic panels as needed to cover the walls and ceiling, if necessary. Someone has already suggested filling the studs with acoustic insulation and covering them directly with sound transparent fabric, which is an interesting idea.

    I'm pretty handy and like to do most of the work myself, so I am open to anything. It looks like I can get 3 levels of seating, so I'll build the risers when the wall plans are solidified.

    I have some pretty good hardware (projector, screen, speakers, receiver, etc), and will probably upgrade several pieces once it is operational, but want to make sure I get the proper acoustics so it sounds as good as it possibly can, before hooking anything up or upgrading. Any help you can provide would be much appreciated. I want to get the walls all built and covered now, so let’s start there first. Also, I am not really concerned with having a visually appealing "theater look". I only want it to sound the best it can. Thanks!
  2. Gordonj Full Audioholic

    Gordonj
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    You could easily just attach the acoustical panels directly to the concrete walls for a cheaper approach. However, since the panels wont need to be floor to ceiling it may look nicer with a drywall finish and then attaching the panels where needed.

    On the open framed wall, does the wall connect to another living space/area? If so you may need to build up that wall to have some mass in order to stop sound transmission to the other space. If you want to build an alcove for trapping acoustical energy you will still need to build a wall system in order to control the tuning of the wall and from keeping unwanted LF from coming back into the listening area (make sense?). My suggestion would be to build all the walls with drywall and then cover the areas that you want with acoustical panels. The one drywall/stud wall, for tuning purposes, i would cover with 2 layers of 5/8" gyp board.

    Gordon
  3. GO-NAD! Audioholic Ninja

    GO-NAD!
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    How "new" is new? I'd personally wait a year before finishing a new basement. Although concrete cures in about a month, it's still not fully dried. Waitnig a year allows the concrete to dry more and will make any settling cracks visible. I may be just over cautious - many new homes have the basements finished immediately. Still.....

    What is the climate like where you live? If it gets really cold in winter or really hot in the summer, you should insulate (thermal) the exterior walls, including vapour barrier, before thinking about the acoustic panels.

    I wouldn't cover the entire walls and ceiling with acoustic panels - if that's what you're suggesting. Such room treatments should be installed where needed to address acoustic problems. Not as a general wall covering. That requires acoustic measurements, i.e. RTA. And, you wouldn't do that until you had the walls insulated. These measurements would then indicate what and where - if any - acoustic treatments are required.
  4. tgoldbeck Audiophyte

    tgoldbeck
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    Good idea, Gordon. I am gathering that putting up drywall first is the best idea, then treat from there. Someone suggested a special layered drywall called Quiet Rock 545, which is supposed to be used for recording studios/home theaters. The whole theater is under my garage, and the space on the other side of the framed wall is my shop/storage, so I'm not worried too much about what sound escapes the room, however, I did not think of the sound coming back in to the theater. The opposite concrete wall is about 25 feet away. Is that far enough away for that not to be a concern?

    GO-NAD...new is one year old. Now that everything else is finished up and we are officially settled in, it is time for the theater. I hear what you are saying with the concrete drying. We ran dehumidifers in the basement non-stop for months to get it to dry. All three floors also have 3 inches of concrete, so we had lots of moisture! I live in Madison, WI, so we have the extremes. As mentioned above, it is all underground, and I monitored it closely throughout the last year, noting temperature changes. The in-floor heat helps keep everything very stable also, so I think we are looking good on the temp side.

    Good idea about treating after the walls are up. Now that I'm getting more feedback, I am understanding the initial suggestion to cover all the walls was probably not the ideal solution. Thanks for the feedback!!
  5. Gordonj Full Audioholic

    Gordonj
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    The quite rock product is a good product and we specify it often for commercial and residential buildings (when appropriate). Keep in mind that the quite rock product is a replacement for typical gyp board. So, instead of specifying 2 or 3 layers of 5/8" gyp board we can spec 1 layer of quite rock product. However, keep in mind that the quite rock product tends to be 3 to 5 times more expensive then 5/8" gyp board (varies depending on the selected product).

    Also, remember it is not for interior acoustic noise control it is for STC noise transfer. So for a HTR a typical wall system would need to be in the STC 55 - 65 range in order to control the transfer of noise to other adjacent rooms. If you are mounting the drywall system onto an exterior concrete wall then it may not be worth the expense to put quite rock on those walls.

    One other thing, Since you have three walls that are concrete against earth and one wall that is a drywall system. You will need to make sure that you build up the drywall heavily on the one wall. If not careful that one wall will resonate. In general, a wall system that is a single layer of 1/2" gyp board will have a resonate frequency in the 400Hz range.

    Have fun.

    Gordon
  6. Norman Varney Audiophyte

    Norman Varney
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    Symmetry, especially between left and right is important to the soundstage. As suggested, build the open frame wall mass up. Two thick, but dissimilar layers of Type C gypsum with RoomDamp2 visco-elastic damping compound in-between for the interior side would be a good, inexpensive performer. If you are not worried about sound transmission, you could leave the other side open, eliminating cavity resonances altogether.

    Expect to need corner traps, treatments at the first order reflection points and some additional acoustic treatments to control reverberation times. I would suggest furnishing with carpet and pad and fabric upholstered seats to help the decay times. Understand that three of the walls will reflect even the low frequencies back into the room. Don't just treat for mids and highs.

    As always, the room dimensions and the speaker/listening locations are your foundation. They will make or break low frequency linearity/articulation and soundstage. Sounds like you have the opportunity to do it right at the beginning.

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