Tumult PR box question

Discussion in 'Home Theater Projects' started by Brad Dixon, Jun 2, 2004.

  1. Brad Dixon

    Brad Dixon Stunt Coordinator

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    Well I'm looking at building a PR'd box to replace my sealed Tumult. My question is if it would be better to go with double walled(1 1/2" total thickness)13ply Baltic Birch or single walled(except for the speaker baffle) and use internal bracing?

    I have access to a full woodshop thru my father. All he asks is that I be able to give him drawings(preferably to scale). He thought he could do the bracing in the shape of an X(when looking down from the top) or it would be simple enough to do the bracing in the form of a "tic-tac-toe" shape.

    His feeling is, even doubled up it may not be as stiff as it should be. This is simply going by the idea of "no such thing as to stiff/strong of a box. Where with the internal bracing you're connecting the walls together both vertically and horizontally.

    I was planning on 22" internal cube if using all the internal bracing otherwise 21" internal cube with 1 1/2" walls.

    Thanks,
    Brad
     
  2. Chris Popovich

    Chris Popovich Stunt Coordinator

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    I built my Tumult PR box using double wall with minimal bracing. If I did it again, (and I am, haha) I'd use single wall with extensive bracing. In my opinion, it makes for a (slightly) smaller, more rigid box.



    Chris
     
  3. Andrew Pratt

    Andrew Pratt Producer

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    I usually do both double walled and bracing...this is DIY after all[​IMG]
     
  4. minhG

    minhG Stunt Coordinator

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    single wall with bracing is pretty darn strong/tight as it is, i can't compare double wall vs single wall w/ bracing. but i think single wall with bracing would be strong enough.


    single wall with bracing already weighs ~60-70lbs, i would think double wall would be even heavier
     
  5. Andrew Pratt

    Andrew Pratt Producer

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    That last sub I built using a blueprint 1203 driver weighed over 110 lbs[​IMG] IMO its hard to over build a subwoofer box...esp when you're using high performance drivers. I mean its not like the cost is that different
     
  6. minhG

    minhG Stunt Coordinator

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    true on the cost, but having to ask for help everytime you need to move the subwoofer gets old quickly...especially if you need to ask the SO for help!
     
  7. Kyle Richardson

    Kyle Richardson Screenwriter

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    Using bracing is always better but depending on your Driver/PR/Amp orientation it may be nearly impossible to fit bracing in that enclosure....its tighter in there than one would think.
     
  8. Brad Dixon

    Brad Dixon Stunt Coordinator

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    OK here is a link to a page with what my father had in mind for the braces: http://home.mindspring.com/~c-b-dixon/

    The drawings aren't exact but close to scale(the top drawing is a "from the top" view). Anyway when we did the sealed box(that's what the photos are of) we ran braces from side to side and then put spacers between them. Basically connecting them together from front to back.

    This time my father thought it would be better to interlock them in someway (with more bracing running from front to back also). That's what the bottom brace drawing is. The notches would allow them to interlock each other.

    Obviously they won't look quite like I have drawn but I figured that would give the idea my father was planning. Three of them would have the notches at the bottom and the other three would have the notches at the top.

    His reason for so much bracing is once you remove material in the braces for the PR's and Tumult to clear there isn't much bracing by them. As there is hardly any wood on them panels anyway I don't see why I need to brace them so much. I understand the top, bottom and back of the box requiring a lot of bracing as they are large pieces with a higher likelihood of flexing, atleast in my mind.

    He has even said it might be wise to double up the panels even with the internal bracing. Again this is my father and I enjoy doing projects with him but he tends to lean to the "if your gonna do it you may as well go all out" side of things.

    Before I spend the money on the wood for this, is this just beyond overkill? My father is only going by what I've told him in that most people believe you can't make it to stiff or strong.

    Sorry to be so long winded just to ask a simple question,
    Brad
     
  9. Andrew Pratt

    Andrew Pratt Producer

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    IMO no. If weights an issue put teflon sliders on the bottom or even wheels....though the sliders should do. That 110 lbs sub I just finished is pretty easy to slide around on the sliders so its not that big an issue
     
  10. minhG

    minhG Stunt Coordinator

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    brad,

    cost should not be a huge issue, if you're building from some kind of birch, you'll end up using 2 4x8 sheets instead of one. So just look into the additional cost of one sheet.

    The better question is what Andrew brought up, will this be too heavy to move around, position etc? I built my Adire Shiva EBS box of almost the same dimensions as your box (22.5 cube). I used braces (2 front to back, one intersecting those two left to right) and it's super strong. I see no need to double it up. And it's a PITA to move around, it weighs 70-80 lbs (made if from MDF).

    But like I said, the cost is pretty minor in the total (it's just wood), if you can live with the weight issue then I wouldn't fight him too much on it. Just tell him he has to help you move it [​IMG]
     
  11. Dean Mar

    Dean Mar Stunt Coordinator

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    Andrew,

    Can you tell us a little bit more about these Teflon Sliders ? I have a double walled Tumult sub that weighs a ton and is hard to move around.

    I assume they are just Teflon coated and you stick them on to the bottom of the sub ? Where can you get them ?

    Thanks
     
  12. Jack Gilvey

    Jack Gilvey Producer

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    I like a single layer of 13-ply BB with bracing. This can result in a box whose own resonance, while not completely damped, is pushed high out of the bandwidth of a subwoofer. It's as acoustically "dead" in a sub app as a really heavy, multi-layer box whose resonance has been damped/pushed below a sub's bandwidth through brute-force/weight.
     
  13. Andrew Pratt

    Andrew Pratt Producer

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    Dean I bought mine at a local hardware store (Canadian Tire) but I expect wal-mart would have them as well. They come in a variety of sizes and my advice would be to get ones that are no smaller then 1.5" wide...the bigger the better within reason so they have more surface area to spread the weight around on. I actually use them quite a bit around the house on items I want to move such as the air hockey table etc as they're cheap and effective.
     

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