Christmas Build - Page 6 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #51 of 103 Old 01-15-13, 12:44 PM Thread Starter
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Re: Christmas Build

See the image below for where this thing is going to go. The screen is 100". The subs just fit underneath.

I am going to cut the wall and frame around the baffle. The baffle is not going to touch any part of the wall because I have seen that even the smallest mechanically coupled vibration can cause undesired effects. The air pressure is going to do a lot to the wall - may as well not add mechanical vibration as well.

Question: I am wondering how I should seal around the baffle. Just use foam or is there a more sophisticated way?

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post #52 of 103 Old 01-16-13, 11:02 PM
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Re: Christmas Build

Looks like an impressive baffle for an impressive looking line array!

I've thought a bit about decoupling and was thinking about attempting something with my upcoming build. I searched around a bit on The Cult of the Infinitely Baffled. One of the FAQ posts (I believe) states something to the effect of "been there, done that, doesn't work" wrt decoupling the baffle. I could not find any support documentation however.

I am considering decoupling mainly because my baffle wall must be floated 2" above the slab in the basement to meet code. (unstable soils)

The idea I had was to support my baffle (manifold in my case) on the concrete slab and design the opening to lay something like 1/4" from the actual (sealed) wall opening. I would then use a rubber airtight seal between the two. I was actually considering cutting some mountain bike tubes and using silicone adhesive to create this seal. I'd probably staple the rubber up to both sides and use silicone around the edges. I don't see having a problem with getting it airtight and I can't really think of any other drawbacks.

WRT your foam idea, I am not envisioning what you have planned so it is tough for me to comment. Can you elaborate more? Closed cell foam between the baffle and the wall, like what one might use as a speaker gasket?
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post #53 of 103 Old 01-17-13, 10:57 AM
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Re: Christmas Build

Almost done! I hope it doesn't flex on you. If it does you can always overbuild later like you said. Steel plate was once recommended to me for a baffle with even better spacing than yours, and I had some pretty stout bracing. Reinforcement could be added to the backside if needed. Expensive, but you had some pretty severe space constrictions.

Here's the plan that Thomas over at the Cult told me I needed steel plate or better driver spacing for. I took i with a grain of salt because it seemed pretty sturdy to me, but ended up going in another direction anyway.





It looked to me like you might get away with it, but I didn't know you were going to recess it halfway into the baffle. That's a considerable amount of stability you gave up by recessing it that far in. All this said though, I can't really understand how you can't make up for it with robust bracing, so it still seems to me like it should be fine with a good bracing scheme. Have you figured out a bracing plan yet?

I'm sorry I don't really have any solid advice for you on decoupling, just ideas like yourself. If it was me I would probably just try for a 1/4" gap around the baffle and caulk it with silicone with a nice caulk line on the front and a little extra on the backside. I would also probably try for a narrow wood trim around the baffle or at least on the sides and the top just to hide the cutout and most of the caulk job if there was any space at all to do it. But a foam like a weatherstripping seal would also work, and the baffle could be removed a little easier there too. The been there done that didn't work is kind of ominous though, I'd chase that lead down before proceeding.
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post #54 of 103 Old 01-17-13, 12:10 PM Thread Starter
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Re: Christmas Build

The baffle is actually going to go into the wall - and become part of the wall - similar an inwall speaker. In the theater side it will be flush with the wall. I am going to cut a big hole in the wall to just fit it in with a tiny bit of space on the top/left/right so I can slide it in and then seal it up I would then simply use molding to cover up whatever gap is left. The bicycle tube idea is very clever. I guess it depends on how tight I can get the gap between the wall and the speaker. If it ends up being larger than 1/4 then I might have to get creative. I am currently thinking some winter door stripping would work with calk for a 1/4 gap. Who knows.... Things keep flipping through my mind. The nice thing about this project is that I have the luxury of trying a few things and then just ripping them out if they don't work.

I agree the baffle is very compromised from a strength/resonance standpoint - even with all the layers of boards. I made it as short and thin as possible to fit in the space. I could add more boards to the back, but I am thinking there are some diminishing returns with that compared to more bracing as described below. I am counting on the bolting to the floor and significant bracing to make it as non-resonant as possible.

Bracing thoughts: The following is all my mind is coming up with for bracing. I have considerable advantage because it is sitting on a concrete floor and is only 20" tall. What should I use for the braces? MDF? What am I missing? Maybe I should add a board across the top along the back that would be notched into the braces for added stability across the top.
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post #55 of 103 Old 01-17-13, 01:25 PM Thread Starter
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Re: Christmas Build

Quote:
vann_d wrote: View Post
Looks like an impressive baffle for an impressive looking line array!
Thanks! I have told my friends that this is a IB subwoofer - to confused looks of course. When I tell them that the design is such that they will be sitting INSIDE the subwoofer - that gets their attention.

I have to wonder how many home IB subs there are in the world? I know people have just thrown drivers in walls - but I don't count that. I am talking about a well designed IB. In my opinion 99.9% of movies before the early 2000s don't have the bass to justify an IB build. So it feels like a young art form. The cult was formed in 99... Maybe a interesting discussion topic.

Quote:
vann_d wrote: View Post
I've thought a bit about decoupling and was thinking about attempting something with my upcoming build. I searched around a bit on The Cult of the Infinitely Baffled. One of the FAQ posts (I believe) states something to the effect of "been there, done that, doesn't work" wrt decoupling the baffle. I could not find any support documentation however.
Hmmm.. I re-read the FAQs and could not find what you describe. I did a few searches and a number of people describe various methods of XPS(extruded foam) or caulking to seal. My sense is that there is no issue with sealing, just with the coupling. Most of the line arrays(that are not build directly in concrete) are not as well braced as mine will be. Given that - maybe there will be very little vibration to transfer and a simple seal will work.

Quote:
vann_d wrote: View Post
I am considering decoupling mainly because my baffle wall must be floated 2" above the slab in the basement to meet code. (unstable soils)
I was afraid that inspector would screw with you . Can you brace it to your back wall of concrete?

Quote:
vann_d wrote: View Post
The idea I had was to support my baffle (manifold in my case) on the concrete slab and design the opening to lay something like 1/4" from the actual (sealed) wall opening. I would then use a rubber airtight seal between the two. I was actually considering cutting some mountain bike tubes and using silicone adhesive to create this seal. I'd probably staple the rubber up to both sides and use silicone around the edges. I don't see having a problem with getting it airtight and I can't really think of any other drawbacks.
From what I have read, you just need to be worried about the seal and not so much from the decoupling given that you are running manifolds. I have heard that a properly designed manifold has close to no mechanical vibrations. The wall is what needs to be braced so as not to be vibrating your subs.
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post #56 of 103 Old 01-17-13, 11:29 PM
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Re: Christmas Build

Quote:
blitzer wrote: View Post

Bracing thoughts: The following is all my mind is coming up with for bracing. I have considerable advantage because it is sitting on a concrete floor and is only 20" tall. What should I use for the braces? MDF? What am I missing? Maybe I should add a board across the top along the back that would be notched into the braces for added stability across the top.
I like your idea but I would not use MDF. I would implement a sort of truss out of 2x4's. MDF is wimpy stuff.
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post #57 of 103 Old 01-21-13, 12:02 AM
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Re: Christmas Build

Blitzer, is your new avatar what I think it is? OK yes I know it is, and why is that your avatar?

Are you holding something out on us?
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post #58 of 103 Old 01-21-13, 05:13 PM Thread Starter
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Re: Christmas Build

Quote:
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Blitzer, is your new avatar what I think it is? OK yes I know it is, and why is that your avatar?

Are you holding something out on us?
At $26,000 installed, they are a little outside my budget at the moment. Have to wait until payday.

Flat response to < 1Hz would be fun with all the new sub-bass coming out in movies these days, but would still need the IB to handle 20-80Hz. At 5Hz and less, this thing moves doors back and forth 1" while playing - it would be a new level of vibration for a house to deal with.

This is the only upgrade I could think up beside adding more drivers to the IB. Gotta plan ahead.

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post #59 of 103 Old 01-21-13, 05:44 PM Thread Starter
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Re: Christmas Build

Easy Fan Mod
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Christmas Build-_bdl5785_dxo.jpg  

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post #60 of 103 Old 01-23-13, 10:23 AM
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Re: Christmas Build

Quote:
vann_d wrote: View Post
I like your idea but I would not use MDF. I would implement a sort of truss out of 2x4's. MDF is wimpy stuff.
Agreed. I'd mimic the original plan as pictured but with a series of triangle braces made of 2x4's. You could clap plywood or OSB to each side of the braces to give them extra strength and stability once you have the 2x4's in place and secured to each other, the baffle, and the concrete.

Last edited by zacjones; 01-23-13 at 10:29 AM.
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2ohm , 4ohm , behringer ep4000 , build , christmas , ib , ib subwoofer , ib318 , magnepan , manifold , minidsp , subwoofer

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