A query about bracing, Sorry for the big pics

Discussion in 'Archived Threads 2001-2004' started by Julian Data, May 15, 2001.

  1. Julian Data

    Julian Data Second Unit

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    I have been working on designing my PR (big) box and I am have been working two different designs in bracing. The box itself has dual layers on the front, rear, and sides. I will be using two 15" drivers and six PRs. Two PR mounted on each side and one driver and PR mounted on the front and rear. Think heavy! [​IMG]
    Anyhow..
    The first design resembles a "cross" in the middle of the thus breaking up the internal box into eight "virtual" boxes.
    Here's an image:
    [​IMG]
    That design uses slits (I don't know the proper woodworking terminalogy [​IMG]) as if you were assembling a box with divider inside. So basically brace would be interlocking. As in the image, brace A to brace b and brace b to c. This by far uses the most wood and probably adds more weight. Each braces intersects at the halfway point/middle of the box.
    The second mimicks what the Aerial Acoustic SW12 has, which looks like this:
    [​IMG]
    So with this design, the braces are in the vertical plane of the driver. And I will place these brace at 1/3 and 2/3 distance in the box. Going perpendicular (horizontal plane), I will add stock between these braces at the top and bottom of the box. Lastly, there will be more stock positioned at the sides at middle height.
    So what is your opinion on which one is stiffer or should I add more braces?
    Thank you for your time.
    JD
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  2. ChrisA

    ChrisA Second Unit

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    Those slits are called "DADO"
    When I constructed the BH subs, I used 1.25 inch thick Marine plywood at $160.00 a 4x8 sheet. It was worth every penny. Perhaps you could use 1 inch thick marine ply? The effective rididity is approximately 2.5 times that of medite MDF. Once you use really thick wood (1" or greater) buttjoints don't need dado grooves cut, as thick buttjoints work fine.
    As far as crossbracing, as long as you use intersecting horizontal and vertical crossbracing then you are doing the best possible job. The Ariel 10T is an overpriced average commercial sub, what's new!!! I like your first design better as the other uses no front to back crossbracing. I also like the shelf bracing in the first design. You can see my choice clearly in the Black Hole Subs.
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    Pictures: The Worm Hole Theater featuring the Black Hole Subs and Death Star Platform
     
  3. Julian Data

    Julian Data Second Unit

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    The "Blackhole" Man has replied! [​IMG]
    Hey Chris,
    I have been going back to your pics on the construction of your subs being that this is the first box for the HT I will be building then it's off do some some monitors for the PC. [​IMG]
    Anyhow, I see that you like the first design. As for the second, remember I was going add some braces along the perpendicular lines of those vertical braces at the center, sides, top and bottom. So there would be front to back bracing.
    So #1 gets one vote.
    I have priced 3/4" Marine Ply here locally and it could be had for 57.50. I'll call tomorrow for 1" but the reason for the dual layers was to get the drivers/PRs countersunk/flush with the baffle. So I used 1" that wouldn't leave me much meant for the T-Nuts to grab and enough thickness for the drivers/pr to mount.
    .. That Aerial is bit high! [​IMG] I know my past subs most likely out performed them handidly [​IMG]
    jd
    PS: Is it possible to do a "roundover" edge on Marine Ply?
     
  4. Hank Frankenberg

    Hank Frankenberg Cinematographer

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    Julian, try laminating: outer layer 3/4" MDF, inner layer 3/4" Baltic birch or marine plywood. That way you get the machinability (your roundover edges) and easier laminating/painting of MDF, and the stiffness of plywood for the inside layer of your cabinet. Plus, I've read that the sandwiching of the two different materials helps in absorbing/dissipating vibes. This is similar to the sandwiching recommended by Northcreek Music. I recommend their Northcreek Cabinet handbook:
    http://www.northcreekmusic.com/Publications.html
     
  5. DanWiggins

    DanWiggins Second Unit

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    Julian,
    The first bracing option would probably be your best bet, since it does brace all "baffles". Additionally, Hank's recommendation of 3/4" marine on the inside and 3/4" MDF on the outside is quite good, too. You get the stiffness of the ply, with the nice finishing of the MDF. Additionally, since the front depth of the drivers are 3/4", there's no partial holes to cut. The MDF is cut all the way through with the OD of the drivers, and the plywood is cut all the way through with the mounting diameter of the drivers. Nice and simple!
    Dan Wiggins
    Adire Audio
     
  6. Julian Data

    Julian Data Second Unit

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    Thanks guys for the tips and suggestions.
    That's 2 for Brace A.
    JD
     
  7. Brian Bunge

    Brian Bunge Producer

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    Julian,
    Make that 3 votes for brace A! So after all that heated discussion are you now going to try the HE15's? [​IMG]
    Brian
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  8. Julian Data

    Julian Data Second Unit

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    HE15? What's that? [​IMG]
    I'll be trying "several" different 15" drivers in this enclosure.
    From PE, Adire, Stryke, Audiomobile.. etc... Well that's the plan. Yet, it will still be undecided on the final 15" drivers will be until after testing.
    Thank God I got all the proper T/S parameters! [​IMG]
    Brace A, huh? I drew up pic of Brace B at HTT and looking at Dan Marx's bracing, it's almost the same but I like his his idea of the center braces being off center.
    IMHO, Brace A is more stiff, Brace B takes less work. Whew!
    I just hope I have the time to finish the box over summer as you know it's "jet skiing" time! [​IMG]
    jd
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