Under Garage Home Theater Build

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ecut1
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Under Garage Home Theater Build

#1 Post by ecut1 »

Hello all,

This will probably end up being a very long build thread but I'd like to get it started. I'm in the process of building a home and we went with a high wall in the garage which will be topped with hollow core concrete. I have two rooms - one is 22'x24' the other is 14'x24'. Those are rough dimensions so the finished room that will house the home theater will end up being right around 13'x23'. I already have two table tubas, a pair of TLAH's, and a curved SLA. I plan to add a Tuba HT (possibly two Tuba HT's). I think it would be ideal to put the Table Tubas in the front corners and Tuba HT's in the rear corners. The door to the room was placed in the center intentionally so I could place sub woofers in the corners.

Some Questions:

1- Being a 6 sided concrete box will the concrete hold the bass waves inside and cause issues with the sound? In my last house the bass traveled upstairs, outside, etc. I'm just not sure what to expect with it all boxed in.
2- I'd like to take advantage of the 9 foot ceiling and put a raised floor halfway through the room. If I put the Tuba HT's in the back corners on top of a wood floor will it cause issues with the sound? I'd most likely just glue some TGI's to the concrete with standard OSB sub floor on top and put a 6 inch step up to them.
3- Given the option to use part or all of the 22'x24' room should I be going that route instead? I've heard square (or close to square) rooms are not ideal but I could frame off whatever size I wanted. Drawback could be losing the concrete box.

Let me know what you think, I'd love some experienced advice on this build. I'll attach a picture, the garages are on the right 22x24 up front and 14x24 to the very right.
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Grant Bunter
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Re: Under Garage Home Theater Build

#2 Post by Grant Bunter »

I guess the answer to your "dilemma" is in the answer to the question "Is your current HT adequate enough that you though 14 x 24 would be fine?"

How high are you planing to build this platform?
It springs to mind that if the platform isn't solid enough to constitute it's own boundary, then the prime directive in the sub sticky comes into play.
ie the mouth cant be within 2 to 8 feet of a boundary without causing cancellation, in your case possible, the floor. Of course that thought becomes redundant if the presence of the corner eliminates it.

It also seems you have totally determined the best place the subs should be is in each corner.
Certainly, in terms of maximising output, yes.
What's your fall back plan if it turns out the best place for each sub is the middle of each wall?

Best sub placement is determined by measurement and experimentation.

Finally, I would think solid concrete walls will probably be the best thing to excite the room nodes/modes. Fall back plan if that's the case should be the statement just above...
Built:
DR 250: x 2 melded array, 2x CD horn, March 2012 plans.
T39's: 4 x 20" KL3010LF , 2 x 28" 3012LF.
WH8: x 6 with melded array wired series/parallel.
Bunter's Audio and Lighting "like"s would be most appreciated...

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Tom Smit
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Re: Under Garage Home Theater Build

#3 Post by Tom Smit »

May I suggest putting insulation in the ceiling, the more the better? It will attenuate the bass frequencies to a degree. Also, a standard stud wall doesn't do much to slow down bass waves, either, A double wall, not joined but separate, along with a double layer of 5/8" drywall will cut down on transmission through the wall. use Acoustic sealant where the drywall makes contact.
TomS

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Bill Fitzmaurice
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Re: Under Garage Home Theater Build

#4 Post by Bill Fitzmaurice »

Tom Smit wrote:May I suggest putting insulation in the ceiling, the more the better? It will attenuate the bass frequencies to a degree.
Insulation has about as much effect on low frequencies as it does on artillery shells and tornadoes. :conf:
Also, a standard stud wall doesn't do much to slow down bass waves, either, A double wall, not joined but separate, along with a double layer of 5/8" drywall will cut down on transmission through the wall.
The same applies to floors. Two sets of joists are required, one to support the floor above, the other to support the ceiling below, with no connections between the two. You'd fill the space in between with insulation, not to stop low frequencies, because it won't, but to prevent midbass and lower midrange resonances from arising in that space.

CoronaOperator
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Re: Under Garage Home Theater Build

#5 Post by CoronaOperator »

He is using hollow-core precast concrete for the ceiling so essentially everything concrete.

Image

Any air gaps would be the biggest source of noise transmission. That door and HVAC would be your biggest sources of sound transmission followed by any openings cut for wiring, plumbing, HVAC, ceiling joints, etc would all have to be meticulously filled in.

For the risers I'd stay it would have the same acoustical properties of a stage. I'd recommend joists on 8" centers if you want it vibration free, 3/4" subfloor, all glued and screwed. The glue is essential to prevent vibrations. Here is how I re-did our stage after adding some serious bass: Image. It is solid now and worth the effort although at 8" centers, I couldn't peek my head down in between to run cable, was a little annoying but everything is glued shut now so no worries.



Being 6 sided concrete, interior sound absorption should be in the plans as well. Walls, ceiling, floors, the full gauntlet.
Built:
17" width 10" driver Autotuba
2 x 29" width dual Lab12 Tuba60
6 x DR250 2510/asd1001
In progress:
2 x DR250 2510/asd1001
For best results, point the loud end of the array towards the audience

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Bill Fitzmaurice
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Re: Under Garage Home Theater Build

#6 Post by Bill Fitzmaurice »

I'd forget about the wood floor, it does nothing to improve the sound in the room. Well padded carpet is a must, though.

CoronaOperator
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Re: Under Garage Home Theater Build

#7 Post by CoronaOperator »

Bill Fitzmaurice wrote:I'd forget about the wood floor, it does nothing to improve the sound in the room.
It may improve the sight lines for the rear seats.
Built:
17" width 10" driver Autotuba
2 x 29" width dual Lab12 Tuba60
6 x DR250 2510/asd1001
In progress:
2 x DR250 2510/asd1001
For best results, point the loud end of the array towards the audience

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dswpro
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Re: Under Garage Home Theater Build

#8 Post by dswpro »

I am kind of curious, would heavy drapery be more beneficial for a media room than a stick frame with drywall? Which would be more expensive?

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Bill Fitzmaurice
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Re: Under Garage Home Theater Build

#9 Post by Bill Fitzmaurice »

You want a framed drywall finish, not bare concrete. Drapes over that as the finish is an option.

ecut1
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Re: Under Garage Home Theater Build

#10 Post by ecut1 »

I think no drapes, just framed walls and ceiling covered in sheet rock. I'll probably do blown in cellulose insulation but I've had some people recommend spray foam insulation. I've seen some home theaters in basements lately where the steps in the floor were actually poured into the concrete. I'm not sure if having the people on the back couch see better is really worth all that money. Normally when we watch a movie we all fit on one couch anyway. Maybe the thing to do would be to build a platform just big enough for the couch and a step in front of it. Then it would be elevated without having to set the rear sub-woofer(s) on the wood platform.

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Bill Fitzmaurice
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Re: Under Garage Home Theater Build

#11 Post by Bill Fitzmaurice »

You will need some sort of treatment of the walls and ceiling, or the reverberation will be unbearable.

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DJPhatman
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Re: Under Garage Home Theater Build

#12 Post by DJPhatman »

ecut1 wrote:I think no drapes, just framed walls and ceiling covered in sheet rock. I'll probably do blown in cellulose insulation but I've had some people recommend spray foam insulation. I've seen some home theaters in basements lately where the steps in the floor were actually poured into the concrete. I'm not sure if having the people on the back couch see better is really worth all that money. Normally when we watch a movie we all fit on one couch anyway. Maybe the thing to do would be to build a platform just big enough for the couch and a step in front of it. Then it would be elevated without having to set the rear sub-woofer(s) on the wood platform.
If the spray foam insulation is available, use it. The spray foam has better thermal insulating properties, and it will provide a vapor barrier. Blown-in cellulose is cheap, but not as effective and provides no vapor protection.

If it were me, I would paint the interior concrete with 2 coats of basement wall paint, then the spray-in foam insulation/vapor barrier, then sheet-rock for the interior finish. Use decorative wall and ceiling fabrics to cut down the reverberations.

If you are going to have 2 or more rows of seating, you really should elevate each row higher than the one in front of it. This gives each seat a clear view of the screen. With careful planning and fore-thought, you can incorporate every element you want into your plan.
I know money often seals the deal, but seriously, quality is an investment, not an expense... Grant Bunter
Accept the fact that airtight and well-braced are more important than pretty on the inside. Bill Fitzmaurice

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Bill Fitzmaurice
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Re: Under Garage Home Theater Build

#13 Post by Bill Fitzmaurice »

DJPhatman wrote: If the spray foam insulation is available, use it.
Where concrete foundations are concerned the insulation should go on the outside, not the inside. That way the concrete acts as a thermal berm, keeping the house warmer in winter, cooler in summer. There should also be a layer of sheet urethane foam on the outside of the framing of the upper stories, to minimize heat loss through the studs.

ecut1
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Re: Under Garage Home Theater Build

#14 Post by ecut1 »

Well, the house build and many other items completely took over my life. I can't believe it's been almost 2 years since we poured the foundation!

I revived the home theater build this weekend. It's all framed and ceiling lights are wired up. I'll be working on electrical for awhile, running speaker wire, etc. I'm not sure if I should just stick with good old 7.1 or look into atmos, etc.

One thing I'm not so sure about is the type of insulation to use. Blown in cellulose seems like the most logical option because of the sound dampening advantages, etc. But then once it's covered with sheetrock it seems like you're right back to the sound reflection issue. I'm planning on building sound dampening frames covered with fabric and some sort of sound insulation behind the fabric. I'd like to cover at least 80% or more of the walls in that manner. What material is best to go behind the fabric and how thick? I was thinking of building wood frames out of 1x2's so behind the fabric would be about 3/4" thick.

Once a theater is to that point would it even make any difference what insulation is under the sheetrock?? Would cellulose even have an advantage over plain old fiberglass once it's all done?

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Bill Fitzmaurice
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Re: Under Garage Home Theater Build

#15 Post by Bill Fitzmaurice »

What's under the sheet rock doesn't matter sound wise, though for R value foam is best. There's no need to go nuts over the sheet rock. If you make the room too dead it will sound bad. My living room has no visible treatments, but the sound is perfect. That comes from full carpeting, an acoustical ceiling, thick textured wallpaper, pleated shades in the windows, and two large upholstered couches.

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