# Small HT build, need acoustical advice



## sga2 (Nov 14, 2009)

I have a small HT build (15'W x 16'L) in my basement. Floor is concrete but will be covered with thick carpet. Walls are drywall (what else?). Ceiling is 2-layer assembly. After packing the floor joists with insulation, I'm applying a layer of drywall. Then I'm dropping a 2x2 lay-in ceiling 6" below that for mounting lights. I will fill that cavity (between drop ceiling and drywall) with 5.5" batts for more sound control. Primary goal is to reduce the sound coming DOWN into HT room from kitchen above (wife walking in heels and dishwasher are 2 major issues). Also, with the drop ceiling, I can acces the space above easliy if I need to pull additional wires in the future.

My 7.2 speaker setup is Klipsch RF-3 fronts, RC-52 center, RS-42 surrounds, and SVS PC12+ (have one, will get 2nd soon...). Primary seating position is 10ft from screen (15'W) wall.

All that said, I know acoustical treatments to smooth freq response is a must. The room dimensions are not ideal, but I can't make the room larger and would rather not make smaller. 

Is there anything i need to consider in the framing stage, before I start hanging drywall?

Also, while I know that I will have to experiment with speaker placement, I'd like to be sure the wall outlets (speaker terminals and 120V for subs) are at reasonable locations so I don't have to relocate after drywall or have too much exposed wire. For planning purposes, I am locating the fronts about 2'9" from each side wall, which puts them within Dolby guidelines (26-30 degrees from screen centerline). The subs, therefore, need to go in the corner (I know the issues there) or between the front and center channels (about 4'6" from each side wall). Can I assume that locating two PC12+ (downward firing) at approximately 1/3 points along the front wall will yield better results than near the corner?

Thanks,
sga2


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## bpape (Sep 14, 2006)

*Re: Small HT build, need acoutstical advice*

I'd recommend framing the stage and any seating riser after the drywall is up. That allows it to be physically disconnected from the rest of the room and not transfer vibrations. This is especially important on the stage where speakers and subs will potentially sit.

One good way to help a bit with footfall is to use another layer of MDF between the joists and screwed and Green Glued to the subfloor above. This increases the mass and drops the resonance of the subfloor without creating a triple leaf situation. 

Bryan


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## sga2 (Nov 14, 2009)

*Re: Small HT build, need acoutstical advice*

Thanks. Your input is always appreciated. 

I'm not planning a stage at this point, but was definitely going to build the riser for the rear seats independantly of the walls.

MDF on underside of floor is going to be a real problem. There is alot of stuff running throught the open web trusses (HVAC duct for upstairs and basement, main electrical service and telco/CATV service, branch circuits, etc.), not to mention about 500 nails from the hardwood floors above. I don't want to touch those nails and potentially mess up the floor.

Would you expect that the triple leaf effect of my proposed assembly (wood floor - cavity - sheetrock - cavity - suspended acoustical ceiling), given that each of the two cavities will be packed with insulation, will result in less attenuation than if I leave the sheetrock layer out?

Also, any input on sub placement?

Thanks,
sga2


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## bpape (Sep 14, 2006)

*Re: Small HT build, need acoutstical advice*

As long as the drop ceiling doesn't have a lot of mass to it and you don't add any, there should be no problems. 

Understood on the nails thing. Bummer.

Sub, hard to say. Every room is different. If only 1 sub, probably either between the mains and the center or along one side wall out a prime fraction (1/7, 1/5, 2/11, etc.) from both front wall and side walls.

Bryan


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## sga2 (Nov 14, 2009)

*Re: Small HT build, need acoutstical advice*



bpape said:


> As long as the drop ceiling doesn't have a lot of mass to it and you don't add any, there should be no problems.
> 
> Understood on the nails thing. Bummer.
> 
> ...


If planning for two subs, would you suggest I start by wiring both locations between the mains and center?

Thanks,
sga2


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## bpape (Sep 14, 2006)

*Re: Small HT build, need acoutstical advice*

In theory as proven by the Harman research paper. 2 subs are usually best either centered on the front and back wall, or centered on the 2 side walls. 

If music is a bigger part of the plans for the room, you may want to live with them both up front so you can do stereo subs close to the mains and run a parametric EQ (not a bad idea anyway) on the subs.

Bryan


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