IB Manifold questions

Discussion in 'Home Theater Projects' started by Tracy_L, Jul 31, 2003.

  1. Tracy_L

    Tracy_L Stunt Coordinator

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    My 2 AV15s are on the way!!!!![​IMG]

    Time to get started on the manifold for the IB setup. I have a couple of questions that have come up during my research.

    I am planning on venting thru the ceiling (huge attic space) centered between the mains above my RPTV. It will actually be about 1.5 feet in front of the front plane of my front speakers, but it is pretty close to being perfectly positioned, at least before hearing it in action, in a roughly 16 x 17 listening area open to entry way, dining area, kitchen, etc....

    I am going to power the two AV15s with a QSC RMX850, which will go up to 830 watts bridged mono at 4 ohms (have not decided how I'm gonna run the speakers/amp yet, still got research to do on that as I'm a little challenged in that area still!!!)

    Anyway, my questions for now are centered around construction. Assuming that I am not going to add two drivers in the future, would I get any better sound from a cube design (18 to 20 inches) over a 20 x 20 x 10 design? Although my wife has been extremely flexible in my desire for a home theater, I would gain those famous brownie points by having a smaller hole cut in the ceiling. But if there is a noticeable gain in the cube design, I am free to do that as well.

    Secondly, I am planning on using leftover maple 3/4 plywood for my material. I had read on the "Cult" where someone used maple 3/4 ply single layer and was pleased with it. I would like to be able to use the same design as far as material and number of layers. And will screws with an adhesive (such as Gorilla glue or similar) be sufficient on a butt joint (correct term I hope) or would using a 2x2 inside at the joint and screwing and gluing to it be better?

    Thanks for any suggestions
    Tracy
     
  2. Rich Kraus

    Rich Kraus Stunt Coordinator

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    I dont know that you gain anything other than flexibility with a cube vs 1/2 cube dedign. should sound great either way.

    Do you already have the amp? 800w is a whole lot of power for a 2 driver IB, even for av15's (now if you were going to upgrade to 4 drivers later.....)
     
  3. ThomasW

    ThomasW Cinematographer

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    The shorter the manifold the better.

    Bracing should be outside not inside the box.

    I recommend using material ~1.5" thick, especially with large heavy drivers like AV-15's.

    The glue will be stronger than the wood; so the only benefit to using secrews is for them to act as clamps while the glue dries
     
  4. Tracy_L

    Tracy_L Stunt Coordinator

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    Thanks Rich & Thomas

    Rich, I've read your description of building your IB at least a dozen times, found it over at the cult. Yeah, I've already got the amp. I haven't decided on the 4 ohm vs 8 ohm yet. It will go 600 watts 8 ohm bridged. I believe that our rooms are similar sized, if remember right. Have you made any changes to your setup since you originally built it? Still happy with 2 drivers?

    Thomas, I guess it's just hard for me to grasp that glue would be stronger than the wood :b I guess I will go ahead and make it double thick just to be sure. Do you recommend making the manifold single ply then adding the second layer, or making each side 1.5" then making the manifold? It seems to me that it may be stronger by making the manifold then adding a second layer and overlapping joints......

    Thanks again for the suggestions
    Tracy
     
  5. Mike Nep

    Mike Nep Stunt Coordinator

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    I finished my IB last Saturday and the design is similar to Rich's. I would build the manifold to accomodate the other two drivers you plan to add in the future. As has been said, build the box as short as possible (read: cube) to avoid any unwanted cancellation and vibration. Also, I would double up on the thickness and make sure you're using void free ply. Also, ensure that the box weight is supported on the joists and NOT the drywall. To do this I used some 1/8" shim stock and placed it between the drywall and the manifold. I then used two 2x4's, which I screwed to the sides of the manifold. These 2x4's rested perpendicular on the joists. I secured these 2x4's to the joists using some heavy duty brackets. After this was done I pulled out the shims and sealed with caulk. As for you wife, if you place an AC grill over the hole it doesn't really matter if your hole is a bit bigger. I'm sure you have vents in your house, what's one more? Good luck!
     
  6. ThomasW

    ThomasW Cinematographer

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    Tracy

    Yeap with rare exception the glue in the joint is almost always stronger than the wood being glued.

    I make an outer 'box' then line it with a second layer of material. But that's just because it's the easiest way to build and I'm lazy. It won't matter which way you create the 1.5"
     
  7. Tracy_L

    Tracy_L Stunt Coordinator

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    I've got 4 pieces of wood glued and screwed together, lol. I used Gorilla glue, and like the bottle says, if you let it get on your skin, it will stain it :b .

    I went with the 20" cube design. Inside measurements are roughly 20x20x19.25.

    Thomas
    Is there any particular reason you glue the second layer to the inside instead of the outside? Unless there is a reason for this, I'm planning on putting the second layer on the outside for my ease and laziness..[​IMG] And how much glue do you use when coating the second layer? Maybe a bead all around the edge and then a squiggly bead inside that? I figured that once I had 8 pieces around the edge, I would top it off with two layers for the top piece.

    Again, it would be easier for me to measure and cut (read as more forgiving, lol) outside pieces than inside pieces. I'm having to cut with a circular saw and a guide I bought from Lowes. The guide is actually helping, but not as good as a table saw, sigh.

    Thanks again for the suggestions
    Tracy
     
  8. ThomasW

    ThomasW Cinematographer

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    Yeap there is a reason for putting it on the inside. The cuts don't need to be as accurate. If you wrap the outside and the cuts are slightly off (particularly if cut too short), it can mess up the fit and finish of the edges of the enclosure. However if they're going on the inside and are a little undersized, they just slide in and everythings ok....

    I only use Titebond II covering the entire surface of each piece applied. I apply it with a brush or roller. It's cheap, strong and doesn't foam all over the place like the urethane glues do
     
  9. Tracy_L

    Tracy_L Stunt Coordinator

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    After 5 minutes here and 5 minutes there, I've finally gotten 8 pieces of wood glued together giving me a 1.5" thick 4 walled cube. Now I just have to put the top piece(s) on her and she'll be ready for the drivers.

    Which leads to my next question. Should I make the top 1.5" (double layer of 3/4 ply)?

    Didn't know if it would be overkill. It won't be that much extra work, since it would really only require me to make 1 more cut to the leftover piece of ply I'll be cutting from (it'll be the same width, just have to cut the length)

    I can't imagine how much this will weigh once the drivers are installed [​IMG]

    Thanks for all of the suggestions so far, I'm sure I'll have more as I go [​IMG]

    Tracy
     
  10. ThomasW

    ThomasW Cinematographer

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    I'd make all the construction from 1.5" thick material
     
  11. Tracy_L

    Tracy_L Stunt Coordinator

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    I have made the ultimate bonehead mistakes!!!! :b

    I made the 20" cube, drilled my mounting holes for the drivers, bought the mounting hardware for the drivers and the manifold itself.

    I went upstairs to start measuring to mount the manifold and found that my rafters are about 14.5 inches apart. Remember, I made a 20x20x20 cube?

    What in the hell do I do now? Is cutting one of the rafters even a viable option? I'm not a homebuilder, so I have no idea... Where I want to cut the hole is about 4 feet from the nearest wall, and about 10-12 feet to the other wall..

    What about putting a 2x6 or 2x8 (or several lengths of each side by side) across 3 rafters with the one I would cut in the middle and putting LONG screws (lag bolts maybe) (and lots of 'em) into it to get support from the nearest rafters

    I'm afraid that I'm gonna have to rebuild the manifold to fit inside the rafters. Damn, I wish I had looked up there about a month ago [​IMG]

    Any suggestion would be appreciated

    Thanks
    Tracy

    ps
    If I decide to rebuild to roughly 20x14 (as tight a fit as I can design, I guess) I think I would have to add around 7.5 inches to the height to make up for the rafters. I don't believe there would be enough room to fit the drivers in the manifold with 7.5 inches of the manifold blocked by the rafter. What I would end up with is roughly 20 x ~14 x ~27.5 high.

    Any comments on this design?
     
  12. ThomasW

    ThomasW Cinematographer

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  13. Tracy_L

    Tracy_L Stunt Coordinator

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    Heh heh

    Nevermind, I called a buddy who is more knowledgeable with this than me and he said cut that rafter, just box it in at each cut. So I'm off to Lowes again to get more wood!!!
     
  14. Mike Nep

    Mike Nep Stunt Coordinator

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    I've never been one to cut through structural entities, but if you're friend is sure it's okay... Just make sure the manifold rests on the rafters at all times and not the sheetrock. It only takes a second for it to go crashing through your ceiling! Good luck.
     

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