Building the platform - thoughts on how? - Home Theater Forum and Systems -

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post #1 of 8 Old 01-30-08, 10:53 PM Thread Starter
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Building the platform - thoughts on how?

Making progress on the HT dedicated room. All framed in and soffit is built. It's time to build the elevated platform for the rear (3 wide x 2 deep) seating. Anyone have any experience with this?
1) Build it directly on concrete floor using a ledger board along back and side walls to nail to?
2) Build it suspended from concrete floor using joist hangers?
3) Build it resting on some sort of rubber or vibration damping material?

What is the best method AND size of this thing . . . thinking of building it around 7.5' from back wall, thus leaving the front row seat backs at 12' from the screen and the viewers eyeballs about 10'

FYI - plans are 106" Screen (was informed that the 110" might be too big)
Room is 19' 3" deep by 15' wide
Projector will be Panasonic 1080P

2 Pics attached:
First is room layout
Second is looking into rear of room through an unframed service entrance (will rarely use this door)
Thanks for any ideas
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post #2 of 8 Old 01-31-08, 10:57 AM
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Re: Building the platform - thoughts on how?

I can't say what the best is (probably the free floating on rubber isolation mounts), but here's what I did:

Ladder frame of 2x8's on the floor. Floating, not fixed to the wall (it touches three walls, so movement is not a problem).

Ran conduit underneath and stuffed with insulation.

Two layers of offset plywood (no overlapping seams), different thicknesses. I did not glue them, since I have needed to get in there to run more wires on occasion. I did use a ton of screws, though. Leave about a 1/2" to 3/4" lip over the edge to make a nice carpet transistion. You could do more, but I was afraid of the plywood breaking with too much overhang unsupported.

Carpet the whole thing, including the vertical faces. I hid poor transition points (carpet to wall and vertical to floor) with molding.

It's solid and doesn't suck the bass out of the room, or resonate.

Be sure to draw plenty of diagrams for elevation to make sure your viewing angles are okay.

So far that's all I have. There's an article somewhere on the internet where someone did their riser as a Helmholtz resonator to help with the bass absorption. If I find it, I'll link here.

Good luck.
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post #3 of 8 Old 01-31-08, 03:55 PM
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Re: Building the platform - thoughts on how?

Take a look at this link

I build mine with 2 x 6 and stacked them together to get a 12" riser ... I didn't stuffed with fiberglass or anything to absorve the sound, but it doesn't vibrate. I used marine carpet (you can find it at Lowes, Home Depot, etc.); I like it because is thin.

If youre planing on using buttkickers, is better if you use isolator to detach the riser from the floor ... it will give you a better experience, or you can use the isolator for every seat.
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post #4 of 8 Old 02-01-08, 10:47 PM
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Re: Building the platform - thoughts on how?

You could certainly be too pedantic about this, but I guess most of us here are just that

If you don't have isolated walls, using isolation mounts on the riser is probably a good idea. I'd green glue everything, and fill the riser with insulation, flattened cardboard boxes, whatever you have that would limit resonance.

Still, not a biggie. Just brace it well enough so there's no flex or creaks!
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post #5 of 8 Old 02-03-08, 03:25 AM
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Re: Building the platform - thoughts on how?

I also can't say what the 'best' would be, but in my case, I built the riser out of 2x12's on top of 30lb roofing felt between it and the concrete so that the wood would not sit directly on it (in case of moisture/wood contact). The top deck was then 30lb roof felt, then 3/4 inch plywood, roof felt, and then another 1/2 inch plywood - all stuffed with insulation and held together with a gazillion screws. The riser itself sits about 1/4 inch away from any wall so that it is isolated (the carpet and baseboards effectively fill in the 'gap' created by doing this). The riser has a solid feel, zero squeaks, and it will not budge even though it is not directly attached to anything structural. I left about a 1.5 in overhang to allow for the carpet to be stapled from underneath, as well as leaving me the option to hide rope lighting there if I choose. As for whether to round off the edges, I asked the carpet guys who did my install, and they advised me that it didn't matter, as the underlay/carpet would bend around with a clean line either way - so I didn't bother to router off the edges.

As for size, yours will really depend on the size of seating you are going to use (including extra space for if they recline), as well as the viewing height of your screen in relation to the front and back row eyeballs. Mine should really have been about another 2 to 3 inches higher, but my ceiling is a hair under 8ft and didn't want to have my head hit the roof (joys of being tall ). If you Google 'riser height calculator', there's a link that might help you make some of your calculations. Another handy tool can be found here:

to help you with decisions on viewing angles and such as well.

Good luck with the build!

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post #6 of 8 Old 02-12-08, 09:41 AM
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Re: Building the platform - thoughts on how?

Here is mine that I built with 4 Buttkickers on the riser:

And here is the whole Theater construction thread:

InFocus 5700 Projector
Marantz SR7002 Stereo Receiver
5.1 Infinity Surround Sound speakers with a Powered 10 inch Subwoofer
Buttkicker Amplifier BKA1000-4A
4 LFE Buttkicker's
DIY 110-inch Movie Screen
DirecTV HD Satellitte Receiver
Modified X-Box with 4 wireless controller's
XBox 360
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post #7 of 8 Old 02-20-08, 12:10 PM
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Re: Building the platform - thoughts on how?

Are you planning on having a subfloor or just carpet over the concrete? You'll need to put down some vapor barrier regardless so that moisture won't creep up and rot your carpet or flooring. A subfloor will make it feel a lot warmer and softer, but you'll loose a couple inches of room height.

I built my risers perpendicularly on top of the sleepers (what the subfloor goes on) with 2x8s and 5/8 OSB on top. I filled them with insulation also which makes them sound fairly solid rather than drum like. The sleepers were 2x2s and 2x4s. 2x4s give more surface to screw into and aren't that much more expensive than 2x2s.

If I could do over again I would probably build the riser separately and rest it on top of the finished floor. That way when I sell the house I could remove it or leave it easily in case the new owner wasn't keen on it.

You can see pictures of what I did here:
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post #8 of 8 Old 03-09-08, 11:27 AM
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Re: Building the platform - thoughts on how?

i would build the riser separate from the walls and other subfloor - use isolation as necessary and fill with insulation to keep it from resonating - although if its high or deep enough, you can use it for buttkickers, bass trapping, and other equipment. leave some trap door panels over the cabling sections in case you need access to them later.
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