Need some design help!

Discussion in 'Amps [BG]' started by V63, Feb 27, 2014.


  1. V63

    V63 Supporting Member

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    Sep 13, 2008
    Does anyone have or know of some sound clips comparing a cabinet without damping and one that has it? How about sound clips of a cabinet that is heavily braced vs. no bracing. I'm trying to get an idea of what to listen to, and shoot for, during my cabinet build.
    http://www.talkbass.com/forum/f15/diy-3015-cabinet-1056453/
    I'd also like to know if putting a nylon stocking over the inside flare of my ports to prevent damping material from entering them would impede their performance.

    Thanks very much.
  2. will33

    will33

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    Bracing, however it is construed, should have the goal of making panels stiff and not letting them resonate (or moving their resonance up far enough in frequency where it doesn't matter. Any enerfy spent vibrating a panel is energy that's not creating sound, or worse, cancelling sound. This means the most bracing should be out in the middle of the panels where they're the most "floppy". Not in the corners like you're building a house.

    Dampening should at least be placed on opposing panels, meaning 3 out of 6. This mitigates internal reflections, smooths resoonse, and helps "even out" the toje so some notes don't boom while others are muffled. Beyond that, location and amount of additional damping is a subjective "tone thing".


    Judge your "tone things" from far away from the cabinet, out where the audience is...not by listening to from one single spot 5 feet away (like where you stand on stage).
  3. V63

    V63 Supporting Member

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    Sep 13, 2008
    Thanks,
    I do understand bracing and damping in theory but I'd just like to know what they "sound" like. I don't want to have take my cab apart eleventy billion times using trial and error if I can help it. It be be nice to know if your cab sounds like "A" then you need more damping, and if sound like "B" them needs less etc. I want a cab the performs well by a modern standard but has a vintage "sound" if possible.
  4. will33

    will33

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    I just now realized you're the same person who has another 3015 build thread going with some of the best minds here contributing to it.

    Sorry, I just don't think I can add anything useful to what's already there.

    As far as "this bracing sounds like this and that bracing sounds like that"...or..."this damping sounds like this and that damping sounds like that".....those are individual design specific things and I don't think generalizations can be made.

    You're back to "if it sounds good, it is good"...which of course, applies in each and every case, regardless if it's studious engineering or pin-tail-on-the-donkey type design. ;)
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  6. V63

    V63 Supporting Member

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    Thank you
  7. DukeLeJeune

    DukeLeJeune Only immortal for a limited time Gold Supporting Member

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    I admire your desire to do the best that you can, and understand that you don't want to be opening up the box and adjusting the damping material repeatedly.

    Regarding bracing, what Will33 said.

    Regarding damping, imo there's a sweet spot for a particular woofer/cabinet combination. The right amount for my woofer and cab may not be the right amount for your woofer and cab even if we use the same woofer due to differences in our cabs' internal dimensions and tone goals. Fortuately, it isn't critical to bullseye that sweet spot.

    Here's what I suggest: Making a "middle of the road" attempt on your first try, and plan on making one revision based on how that first try sounds. Given what my experience has been with the 3015 (non-LF), I'll offer suggestions.

    Usually the most difficult internal standing wave will be in the longest internal dimension, and the easiest to deal with will be in the shortest internal dimension. This is because short wavelengths are easier to absorb than long ones.

    The internal path lengths in a cab are short enough that the reflected energy is going to have many, many encounters with even a small patch of damping material within a fairly short time interval. It's not like a bare patch = that midrange energy survives unscathed; rather, it only survives the first bounce unscathed.

    So as your ballpark starting point, here's what I suggest, assuming 1" thick convoluted foam: 40% coverage of the total combined surface area of the top and bottom of the cab (assuming that's the longest dimension), divided up however you want. You can cover 40% of each, or 80% of one or the other, or something in between.

    Next, 20% coverage of the total side surface areas, again divided up as you see fit.

    Finally, 10% coverage of the total front & back surface areas (consider the woofer cut-out to be flat). Might as well put it all on the back panel, so that would be 20% coverage of the back panel.

    Now, re-assemble and listen critically to your bass, but you may also want to try fullrange program material, as for me at least that's easier to use for judging the midrange. I like to use male vocal + acoustic guitar. With the 3015 you should hear a slightly barky tone in male vocals, but not to the point where it's painful. And your bass should have pretty good thump in the low end, and a bit of upper-mid growl.

    If the cab sounds lifeless and/or the thump isn't there, decrease the amount of damping material. By how much? That's a judgment call of course, but whatever you do will probably be an improvement. Maybe cut the total in half if you want to make a pretty big change. If it sounds good to you, it's okay to go all the way down to zero damping material. In some cases that works quite well.

    If the cab sounds too edgy and irritating, then add damping material. Maybe double up if you want to make a pretty big change.

    Hopefully you'll only have to go through one cycle of refining like this. I don't know for sure that this is the most efficient approach, but it's pretty much what I do.

    If you're using threaded inserts of some kind, you can do this a lot. If your screws are just going into plywood, don't super-snug them for this testing phase. If you want to rehabilitate the screw holes at some point, get a toothpick and swirl wood glue around the inside of the screw holes. Let it dry for a couple of hours, and do it again. Then let it dry overnight, because you don't want the glue sticking to the screw itself. Now your screw holes should be good as new, maybe even better.
  8. V63

    V63 Supporting Member

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    Sep 13, 2008
    Thanks Duke for all your help on this and my build thread! I will do exactly as you say.

    Thanks again. You're a real valuable resource.
  9. DukeLeJeune

    DukeLeJeune Only immortal for a limited time Gold Supporting Member

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    You're quite welcome. Remember my advice is free, and worth every penny!
  10. fnordlyone

    fnordlyone Supporting Member

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    Duke "Cajun Man" LeJueune kicks facts like a Mule Millipede :)
    Will33? he's all right with me
    OP? take it from fnordly, yes indeed!
    Do what Duke says… can't get into all the reason's why right now but Cajun Man is using a tech to get you to what you need in the "real world," not some imaginary land/lab where cabs and speakers are tested to give you all those fancy numbers that should tell you exactly how it should sound.

    http://mariobon.com/Articoli_storici_diffusori/bose_1.pdf

    this is a couple of articles by Amar G. Bose… not perfectly scanned but I think anyone can figure out the scan-typos.

    dude put microphones in crash test dummy ears front and center of the Boston Symphony (weirdo :eyebrow:)

    f n o r d !

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