# Concrete Vault Home Theater - Lots of questions



## seattle_ice (Jul 12, 2006)

I recently finished building our new house, and am now getting ready to finish construction on the theater below the garage. The three car garage floor is a 3" concrete slab on top of wood framing, and under that is a 8'7" high space with a poured concrete slab, that houses the house mechanicals in one spot, and the rest will be the theater. 3 walls, the floor and the ceiling are all concrete, and the walls are 12" thick, so there is only one wood framed wall currently.

I am attaching two pictures below that show the room and a floorplan to help illustrate what I am talking about.

The first questions I have are these:

1. Is it a good idea to mount the front center channel just below the screen?

2. I am planning an IB sub array either in the front left corner, or below the center channel and screen in the center. Probably (4) 15" or 18" subs, using the space behind the screen wall (2' x 8'7" x 14'). Which location would be better? Would this amount of subs be sufficient for the space? What drivers would be recommended for this setup and how much power to drive them?

3. I am contemplating mounting the surrounds at the wall-to-ceiling corners facing down at an angle. Is this ok? What would be better? (Note - the seating will be flush against the left hand wall.)

4. What is the approximate distance a ceiling mounted projector needs to be away from the screen for a 9' screen? I am going to do the screen as a 2.35:1 with hinged black panels to hide the edges for 16:9. How far from the screen should the seating be? (There will be two rows of couches/seats and the back row is an eating bar with stools) How high off the floor should the screen be?

5. Where can I buy a popcorn and soda dispenser cheap?


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## John Simpson (May 10, 2007)

This looks as if it's going to be a fantastic setup. There are some things that will make it even better, though...



seattle_ice said:


> 1. Is it a good idea to mount the front center channel just below the screen?


Yes, this is the second best position it can be in, with the tweeter(s) flush with the surface of the screen. The *best* position is actually behind the screen, one third of the way up the height of the screen. If you intend on building a cavity for the centre channel, you should look into this, with an acoustically-transparent (AT) screen.

I'm a little concerned about the position of your left and right speakers, though. Ideally, with a 9 foot screen, the cavity behind the screen can be big enough for all three channels. See my diagram under "The Wychwood Project" thread to see what I mean.




seattle_ice said:


> 2. I am planning an IB sub array either in the front left corner, or below the center channel and screen in the center. Probably (4) 15" or 18" subs, using the space behind the screen wall (2' x 8'7" x 14'). Which location would be better? Would this amount of subs be sufficient for the space? What drivers would be recommended for this setup and how much power to drive them?


IB is definitely the way to go. Again, look at "The Wychwood Project" thread to see the placement of my two IB manifolds. In that diagram, I have them directly below the centre channel -- there's a bit of discussion going around that they should be off-centre to each other, to avoid nodes along the centre axis. From researching this, I'm inclinded to think it's not enough to worry about.

IBs are fairly forgiving, just so long as you put the main manifolds at the front of the room and build them strong enough to avoid rattles.




seattle_ice said:


> 4. What is the approximate distance a ceiling mounted projector needs to be away from the screen for a 9' screen? I am going to do the screen as a 2.35:1 with hinged black panels to hide the edges for 16:9. How far from the screen should the seating be? (There will be two rows of couches/seats and the back row is an eating bar with stools) How high off the floor should the screen be?


This is an oft-repeated question, because it's not straight-forward. Every projector has a different throw length, with some having a very tight sweet-spot. I've been advised to buy the projector and then place it according to its specs -- kinda tough when the projector sits in a custom-built bulkhead!

Optimal seating distance varies, depending on who you talk to. There are calculators online, but most of these are for 16:9 screens. Anamorphic screens have _relatively_ less horizontal movement, so seating can be closer without "ping-ponging" -- for my 2.9m wide 2.35 screen, THX optimal distance is 3.52m. (This seems ridiculously close I know, but it's based on measurements from the William Holden Theatre, one of the world's best THX-certified cinemas.)

For that size screen, the screen should sit about 800mm off the floor -- although this will depend a lot on your seating. Test out your seating position first, and mark a line where your eyeline hits the wall. This should be one third up the height of the screen.




seattle_ice said:


> 5. Where can I buy a popcorn and soda dispenser cheap?


What is it with Americans and snack machines? :innocent: The last thing I'm thinking about right now is what to eat in the cinema... I'm more concerned about how to pay for it all!

Best of luck! And keep asking questions if you have them...


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## Sonnie (Apr 11, 2006)

Yeah... this looks like it will end up being a dynamite setup... :T

In reference to the IB... I don't know exactly how much space you will need, but make sure you have enough. If needed you could always make a small opening into the utility service room. Something else to consider that will actually be a tad cleaner and give you a little more extension is to go with an SLLT design. Check out SteveCallas' LLT Explained thread and Rodny's IB Makeover thread for more details. If you are on a budget, you could probably save some money, do a pair of 18's in an SLLT design and use the extra money towards something else. I suspect a pair of 18's in an LLT will do all or more than 4 drivers in an IB array, but you would want to model both and be absolutely sure.

As far as popcorn machines... I got mine, as well as several other members, from Roman at Ultimate Home Entertainment. Ultimate is a forum sponsor and you can get a pretty good deal on a popper. It's undoubtedly the best popcorn I've ever eaten and so says everyone else around our office and home. 

I'm looking forward to following your progress. Remember if you need your images hosted we can oblige via the Image Gallery for free.


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## santora (Jul 31, 2007)

That's a lot of space under a garage. As I spent the bulk of my life living near the ocean (at sea level) a basement was never a great idea - at least without sump pumps! :heehee: Do you have to worry about water and all of that? I ask because I noticed you're in Washington State @ Lake Stevens...

Anyway, it looks like you've got a great set up ready to go. We'll be expecting pictures as the construction moves along! :yes:

Good luck on your project!


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## seattle_ice (Jul 12, 2006)

John Simpson said:


> Yes, this is the second best position it can be in, with the tweeter(s) flush with the surface of the screen. The *best* position is actually behind the screen, one third of the way up the height of the screen. If you intend on building a cavity for the centre channel, you should look into this, with an acoustically-transparent (AT) screen.


I have no experience with screens of this type. Are they really 'Transparent' to sound? Does it affect the quality/brightness of the projection? What does a good one cost (say 108" dia.)?




John Simpson said:


> IB is definitely the way to go. Again, look at "The Wychwood Project" thread to see the placement of my two IB manifolds. In that diagram, I have them directly below the centre channel -- there's a bit of discussion going around that they should be off-centre to each other, to avoid nodes along the centre axis. From researching this, I'm inclinded to think it's not enough to worry about..


What about doing an IB with no manifolds - like (4) forward facing drivers? Would you need to hang the screen so it was not mechanically coupled to the same wall for vibration? I am also considering a Sonotube Sub like one of Steve Callas' designs, so I could take it with me as we are going to sell this house in 3-4 years.




santora said:


> That's a lot of space under a garage. As I spent the bulk of my life living near the ocean (at sea level) a basement was never a great idea - at least without sump pumps! :heehee: Do you have to worry about water and all of that? I ask because I noticed you're in Washington State @ Lake Stevens...


We are on a hill so we don't get much standing water. The foundation was also waterproofed with a spray-on rubberized coating 135 mils thick prior to backfill and has very good drainage installed. The basement walls are bone dry. I built the whole house myself, so the quality of construction is exceedingly high.


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## John Simpson (May 10, 2007)

seattle_ice said:


> I have no experience with screens of this type. Are they really 'Transparent' to sound? Does it affect the quality/brightness of the projection? What does a good one cost (say 108" dia.)?


There is *some* high frequency attenuation, but not enough to run these companies out of business :neener: I can't tell you the US price, but a custom-made 150" screen here will start at about A$5000.




seattle_ice said:


> What about doing an IB with no manifolds - like (4) forward facing drivers? Would you need to hang the screen so it was not mechanically coupled to the same wall for vibration? I am also considering a Sonotube Sub like one of Steve Callas' designs, so I could take it with me as we are going to sell this house in 3-4 years.


Yep, an infinite baffle with all speakers pointing the same way is called "in-line". Technically, this is superior to a manifold arrangement, as there's no discrepancy between driver size and the size of the manifold opening.

HOWEVER (and the main reason I'm not doing it): four massive drivers will impose force against the wall, which can create flex (dininishing the effect of the sub) and rattles. It won't knock down your house or anything, but it can have a detrimental effect on plasterwork and will probably move your screen.

Whatever you do -- reinforce!


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## Guest (Sep 20, 2007)

Looks like a Great set up, how much thought have you given to acoustic treatments. As John mentioned I would try to get your LCR behind the screen or below if you do not want to buy and AT screen.

Ty


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