Question about riser construction

Discussion in 'Home Theater Projects' started by Jim Mcc, Aug 1, 2005.

  1. Jim Mcc

    Jim Mcc Producer

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    What is the best way to build a riser 13.5" tall? 2X12's and 3/4" OSB only gives me 12" height. Is there a better way than using 3 pieces of 3/4" OSB? Thanks.
     
  2. Gerald LaFrance

    Gerald LaFrance Supporting Actor

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    they dont make a 2x14???
    you could rip a 2x4!! to desired size needed but that would be alot of work unless you ripped them at the store with there wall saw!! [​IMG]
     
  3. Mark McGill

    Mark McGill Stunt Coordinator

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    I got to ask, why do you need them so tall? Even non reclining seats usually only require 10" max.
     
  4. Kenny WH

    Kenny WH Stunt Coordinator

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    I agree, my 12" riser is more than high enough. My theater seats have pretty tall backs when not reclined and 12" is still plenty. Though the bottom of my screen is about 40" off the floor.

    If you need more than 12" you can always run 2x4's on the floor as a base for the 2x12's. Just run them perpendicular to the 2x12's. You could probably go bigger than 16" centers with the 2x4's since the 12's are very stout. Laying the 2x4's on the flat should get you that extra 1.5" or so you need.
     
  5. Adam Gregorich

    Owner

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    According to an article in Home Theater Builder Magazine written by Dennis Erskine they recommend three layers of T&G plywood: 3/4, 1/2, then 3/4 with roofing felt in between. What ever size 2x you use make them 12 inches on center. This is how I constructed my platform and it is rock solid. I will try to get some pics up later today.
     
  6. Jim Mcc

    Jim Mcc Producer

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    Thanks guys. I used the "Riser Calculator" at AVSforum.com and it says I need a riser of 14-7/8" tall. The problem is my screen is 27" above floor(all the way to ceiling). I don't need T&G plywood because the riser only needs 1 sheet.
    It will be for 1 row of 3 seats in rear. I'm still not sure I can do this because my ceiling is only 6'8" tall. That leaves me 5'5" between top of riser and ceiling. I want to do a step up and then you would sit down without walking or fully standing on riser. I saw a couple pictures at AVS that guys posted that showed this working with low ceilings. The rear riser was 6-8" deeper than the front of seat(just enough to allow you to rest your feet when seated). Am I dreaming thinking this will work? I recently received 6 free theater seats that we re-upholstered and painted, and I want to do 2 rows of 3 seats. The front row I will bolt to a 2X12. Any advice?
     
  7. Kenny WH

    Kenny WH Stunt Coordinator

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    Jim,

    IMO 8" wide seems a little narrow for such a high
    riser(12"+)even if it's just intended for a step-up/pivot/sit down action. Maybe add a step to cut the height so it'd be easier for people to get up there. I have a 6" tall step on mine and makes it very simple to get up and down, plus it gives the riser a more "finished" look. Just think about trying to step up 14" onto an 8" wide landing while trying to turn to sit down.

    You might also want to think about lighting it somehow so people can see where it's safe to step. I let my plywood overhang creating a lip. Then I mounted white rope-lights underneath. I plugged the rope-lights into a switched outlet which in turn is connected to an x-10 dimmer wall switch. This way I have both local control at the switch and remote control via the x-10 setup I run in my theater. During a movie I dim it down so their is just enough light to separate the edge of the riser from the step and floor. The lip keeps direct light from reaching the riser occupants eye's.

    Don't worry about the single thickness of plywood, my riser which is 16'wide x 8'deep x 12" tall only has 3/4" t&g ply. We glued and screwed the ply to the 2x12's and the 2x12's were Liquid-Nailed to the concrete floor and screwed to the wall framing on the two sides it touches the wall. I have 4 large reclining theater seats on it and it's solid as a rock. Vibrations are minimal and I have two LARGE dual-woofer subs in the room. I think both screws and glue are the key to a "dead" riser.

    Sorry for the long post(hope some of it was helpful[​IMG]).

    Ken
     
  8. Jim Mcc

    Jim Mcc Producer

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    Thanks Ken. I will have a step/walkway 1/2 the height of the riser. The 8" I was referring to was the amount the riser stuck out in front of the rear seats to rest your feet on while seated, and to use as a step/pivot to sit down. I'll probably have to make it at least 10" wide. The 1/2 height step would be the "walkway" to the rear seats. Also, it appears I need to fill the riser with insulation, even if it is just used for seating? Is that correct? My sub is in the opposite corner of room. Thanks.
     
  9. Kenny WH

    Kenny WH Stunt Coordinator

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    You can certainly use insulation in the "bays" between the joists if you want to but I didn't and after 3yrs of using the riser I don't feel I need to add insulation.

    My riser is completely carpeted(both vertical sides and top) with normal carpet pad on the top only.

    IMO if the riser is securely built(physically mounted to the floor and/or walls) with screws and glue I don't think it's going resonate much anyway. IMO rigidity and mass is what were after in the riser. If it can't move...it can't resonate.[​IMG]

    My theater is in the basement so I had to mount mine to a cement floor using "heavy duty" Liquid Nail. When the bass is really pumping and I step from the concrete up to the riser, there is very little difference in the amount of vibrations I feel. Don't get me wrong...it does vibrate a little more than the billion-ton slab...but surprisingly not much more so. [​IMG] Both of my subs are sitting on the concrete slab but the side of one sub is actually touching the edge of the riser and the other is about four feet away.

    When I said I have two large subs...one is a d.i.y. unit i made with dual 15" dvc's from partsexpress and the other is a JBL Professional model with two 18's that is THX certified for use in large cinema's. It's about as big a refrigerator lol.[​IMG] All together I running about 2600watts rms into the subs. Believe me...if a riser was going to resonate...it'd be mine.[​IMG]
     
  10. David Noll

    David Noll Stunt Coordinator

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    I never understood why this thick! A normal load carrying floor (refrigerators, etc.) is only one layer of 3/4" t&g plywood or strand-board sub-flooring. I think a 2" thick floor to put seats on is way overkill. I used 3/4" Advantec T&G sub-floor glued and screwed and it is plenty.

    David
     
  11. Andrew Stoakley

    Andrew Stoakley Stunt Coordinator

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    Couldn't agree more David. I used a standard wall construction for my riser, filled the cavities with Roxul Safe N' Sound and then used 3/4" construction grade plywood for the top. I then used Liquid Nails to glue it down and finished it with 1 1/4" screws to secure it. Works fine and you can't hear the riser squeek, squak, moo or bark [​IMG]

    Cheers,
    Andrew
     
  12. Jim Mcc

    Jim Mcc Producer

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    I finally got the riser built and carpeted, and the seats mounted, and it turned out great. The AVS calculator was off by about 3.5 inches. I was able to go with a 10" tall riser, with an extra 2X10 under the seats to raise the seat another 1.5"(total of 11.5" inches and AVS said 14-7/8"). My son is 6' tall and I can see the entire screen plus about 1" to spare. Thanks everybody.
     

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