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A question for the cab builders

Discussion in 'Amps and Cabs [BG]' started by Kawai-chang, Aug 15, 2012.


  1. Now this is just a "Hmmmm, that might work". kind of question, so no flamey me.

    Bracing is done to keep the panels from moving, by pressing from the inside out.

    Could you do the same thing with a small piece of braided wire and a turnbuckle drawing the panels inward?

    Just drill a hole in the panel or use a fixing point on the inside, anchor the wire and use the turnbuckle to tighten to "spec", then Loc-Tite it in place.
     
  2. will33

    will33

    May 22, 2006
    austin,tx
    You could. Don't know that it would be any easier or less expensive. You'd need a sort of anchor that pulled from the outside of the panel inward. Like putting t-nuts in from the outside with the bolt fastening into them from the inside. Keeping things airtight is an absolute must. Recessing/covering them so you don't have bumps in the finish, etc.
     
  3. bobcruz

    bobcruz

    Mar 10, 2004
    CA
    With multiple eyebolts screwed into the inside, you could run a single wire side to side, front to back and top to bottom, then tighten it down with a single turnbuckle. Unfortunately, you've just created a piano, and those strings WILL vibrate with all the sound waves inside the cab. If there was a way to damp the strings completely, it might work.
     
  4. It would keep the panels from flexing outwards, but not inwards.
     
  5. will33

    will33

    May 22, 2006
    austin,tx
    I'd think if you put enough torque on them it would create enough stress tension on the panels they couldn't flex at all.

    Didn't think about the piano thing.
     
  6. Mehve

    Mehve

    Jun 2, 2012
    Kitchener, ON
    I don't know that it would even completely prevent outward flex - braided cord of any material virtually always has at least a tiny bit of outward stretch, simply because it's technically impossible to make a weave 100% tight. Maybe solid core wire? Once things were tightened down, the wire shouldn't be subjected to any further motion/cycling, so there wouldn't be a danger of metal fatigue.

    I'd also be skeptical of the long-term use. Since this solution involves pulling on a wooden panel for a long period of time (probably through numerous temperature and humidity cycles), you're pretty much guaranteed that the wood will simply bend inwards over time, requiring you to retorque the system to maintain the tension.

    Also, metal tends to be good at keeping energy moving, rather than absorbing and dissipating it. If you did do this, maybe some sort of high-strength monofilament? The latest fishing lines can be had in some really high-strength designs for big-water fishing, and one of the biggest marketing claims is "Zero stretch" .
     
  7. Under what kind of circumstances might a panel flex inward during normal cab use? Not being facetious, just curious.
     
  8. If it flexes out, it flexes in. An impulse on the surface may not push the panel out, but it will still rebound in some fashion.
     
  9. Not to pick a nit, but when you say"...it flexes in", do you mean it flexes inward (concave) of it's "neutral" position of straight/flat? Or did you mean it returns to the neutral/flat state after being flexed outward (convex?)
     
  10. It doesnt matter. If an un-braced panel flexes out, then it is also flexing in. When you pluck the sting on your bass "down" it will vibrate down, but also up. If you "brace" that string in the middle by pressing it to the fret board and pluck it, you have not eliminated the vibration in any direction, only limited it on the other side of your finger.
     
  11. astack

    astack

    Nov 12, 2011
    St. Louis, MO
    Get out of my brain! I've been tinkering with the idea for a bit now, too, and I think everyone's so far hit all the same point's that came to my mind and then some.

    For me, I would consider it just for the geek factor. I'm a structural engineer, and we use "post-tensioning" like this a lot.

    It's a similar concept to a truss rod, actually. So, it's not a totally nutty idea in MI.

    This is one problem. Wood will creep under constant stress. I often see fences with 2x4's laid on their side that have sagged a bunch over time because of this, just under self-weight.

    The fishing line is what I settled on, too, after considering picture wire and threaded rod, based on weight, required strength and that damping problem.

    Yup. Those pressure waves are as much suck as they are blow. So any outward peaks are followed by inward valleys.

    Here's some fun numbers for how much it'd have to "fight:" Take a crazy loud, ear-damaging enclosure at 135dB. That converts to 2.3 lbs/sq ft. That's less pressure that another sheet of plywood laid on top of the cab. Multiply that by the area of the panel, and that's about the minimum tension you'd want to apply so that at max outward, the wire tension would be double the initial, and at max inward, it still doesn't lose tension. For a 1'x3' panel that's 7lbs.
     
  12. Astack, stop that, you're making my brain hurt.
     
  13. bobcruz

    bobcruz

    Mar 10, 2004
    CA
    Seems like filament would still have the piano string issue, except it would be more like guitar strings. The cabinet sides would make a nice sounding board to transmit the strings' vibration to the exterior, no?
     
  14. will33

    will33

    May 22, 2006
    austin,tx
    Gives a whole new meaning to tuning the cabinet.
     
  15. kraigo

    kraigo

    Jun 21, 2007
    Minneapolis, MN
    I'd say that the resonant frequency of both the string and the panel when the string is under tension would be too high to really be an issue. I think that if you used something like a T-Nut and some sort of thread lock to keep it from backing out you'd be in reasonable shape.

    As far as "only stopping the outward motion", unless you have expansion/rarification you won't have oscillation, so it makes a reasonable amount of sense. It would take up less internal volume than bracing, which means that the cab could be SLIGHTLY smaller.

    All that said, bracing doesn't take up that much volume, so the additional size that bracing requires is quite negligible with regard to the final size of the cabinet. I think a well glued in brace would be a lot less likely to be a failure point some time in the future. I will still use glued in bracing.

    KO
     
  16. barryaudio

    barryaudio

    Feb 9, 2012
    Massachusetts
    Authorized Builder: fEARful bass, greenboy designs, Bill Fitzmaurice
    Not a good idea:

    - the stress on the panels created by the tension will cause them to warp
    - you would need to continually adjust for humidity and temperature differences
    - as stated above, you would get a piano string effect--maybe give you some natural reverb??
    - bracing not only adds strength, but it also divides up panel resonances. By diving a panel in half, you double its resonance frequency and so on. Unbraced panels will resonate in the mid-bass causing a lot of distortion

    anyway, good gedanken experiment ;)
     
  17. astack

    astack

    Nov 12, 2011
    St. Louis, MO
    It'd be an interesting experiment to see. No easy/worthwhile way to figure it all out before for this application.

    A thing to note, too, is that this would add stiffness but not strength. Bracing fins (ala fearful plans) would add both. Another trade off.
     
  18. Cutty

    Cutty

    Jun 25, 2006
    U.K.
    I would think that the wire would vibrate making all sorts of humming/buzzing noises in the cab,not a good idea IMO.
     
  19. HertzWhenIPlay

    HertzWhenIPlay

    Jan 15, 2011
    I like things that go BOOM
    you could wrap the the outise of the cabinet with braided wire and call it art?
    would have lots of structual integrity...
     
  20. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Use fishing line, tune it to play a sitar-like drone note :)
     

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