Room Dimensions, Screen Size, etc.

Discussion in 'Home Theater Projects' started by Coy, Oct 27, 2004.

  1. Coy

    Coy Auditioning

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    Our plans are for a dedicated Home Theatre in the new home we are building. It will be in the basement (two walls concrete) with room dimensions of 10' ceiling, 16' wide and 23'4" long, with two risers - first riser starting 15'4" from the front wall and extending 4' back, with the second riser immediately following.

    FIRST QUESTION - how high should the risers be?

    SECOND QUESTION - should we "pour" the risers (and stage under screen) to include them with the concrete when the floor is being poured, or should we build them after the floor is in?

    THIRD QUESTION - what screen size would be best for the room dimensions I have outlined, what would be the optimum viewing distance, and what would be the best height for the screen from the floor?

    FOURTH QUESTION - front and center channel speakers - should they be mounted to the side and below the screen, or should we incorporate behind the screen speakers?

    FIFTH QUESTION – should the 7 channel surround back speakers be placed on the back wall, with the 2 side surrounds positioned in line with the first row of seating?

    SIXTH QUESTION – one or two subs and the best placement?

    SEVENTH QUESTION – is it best to rack all components towards the back of the room? What type of venting is best?

    EIGHTH QUESTION – what is the best method for soundproofing and what is the best floor covering?

    Answers to any of the questions would be greatly appreciated.

    Also, any suggestions you may have that would make the HT go together a little better (easier) are also welcomed.

    Thank you!

    Coy
     
  2. Jay Mitchosky

    Jay Mitchosky Producer

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    If you're serious, then it's a room within a room. Literally. The inner frame of the theater at no point comes in contact with the outer frame. This is usually supplemented by having the studs staggered relative to each other. The ceiling joists are hung off the inner frame, typically between the floor joists proper. At a minimum each frame is insulated with an air gap between. Products such as Acoustiblok can be added to further suppress noise. Some swear by resilient channel, which decouples the drywall from the studs, while others think it does more harm than good. Plan for two layers of drywall, each of different thickness as they will vibrate differently, and with their overlapping seams staggered.

    That's the easy part...

    You also need to have every nook and cranny, including electrical outlets, filled with acoustic foam. To paraphrase Ian Malcolm from Jurassic Park, "Sound finds a way." Your entrance will be the single biggest hole in attempting to isolate the room. Plan on a freakishly thick and insulated door, exterior grade with weatherstripping, as a starting point. But this still won't completely isolate the sound. For that it's all about the lead, baby. Huge vault like doors are used in recording studios to completely seal the place.

    Now that you've got the room tight from sound it's also tight from air. So you need to move a lot through so it doesn't get stuffy. But that in and of itself creates noise. To reduce HVAC noise you need to have a number of hard right angles in the trunking, and they need to be lined with acoustically absorbant foam. Ideally you should also incorporate a silencing plenum that acts as another sound buffer. To reduce air noise you need to reduce speed and turbulence, and therefore use wider pipes, wider outlets, as well as diffusers to smooth the flow.

    Floor covering is typically carpet, and you should plan for a floating floor on concrete to help aborb some energy. This floor should be decoupled from any other surface.

    If you're still with me you probably realize what is involved here. So use the term "soundproof" sparingly unless you're willing to go all the way. The Widescreen Review reference theater achieved this - that room disappears when the door is closed. Completely gone even when the insight is humming at reference level. The most you hear is the odd thump when bass gets really intense, but it's about as loud as a balled up sock hitting the floor.

    I am not making this up.

    But they invested an incredible sum of money in that room. If you can track down backissues of WSR they actually detailed every element of construction. Quite fascinating actually.
     
  3. Coy

    Coy Auditioning

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    Jay,

    Fantastic! Thanks for all your time and expertise.

    Regards,

    Coy
     
  4. Jay Mitchosky

    Jay Mitchosky Producer

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    Looking back I think I misinterpreted one of your questions:



    On second glance it looks like you were talking about a traditional floor with concrete stage and riser after the fact. What was in my mind was having a sunken area up front for the first row. So the second tier is actually at the same level as the rest of the basement floor, and you walk down to the first row.

    I wouldn't recommend you build a concrete riser and stage. Too expensive and overkill. Traditional wood framing with a stack of 3/4", 1/2" and 3/4" plywood on each gives you a rock solid base. The "dig down" method would be a better way to go IMO.
     
  5. Coy

    Coy Auditioning

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    Thank you for the additional information.

    Coy
     
  6. Conrad Ebel

    Conrad Ebel Agent

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    I made my riser 11" high. This provides enough clearance for the second row. I wouldn't want any lower than that.
     
  7. Jay Mitchosky

    Jay Mitchosky Producer

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    Same with mine. 2x10s (which are actually 1 1/2 x 9) with 2" worth of stacked plywood for the deck.
     

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