Enclosure thickness?

Discussion in 'Archived Threads 2001-2004' started by PaulDF, Sep 22, 2002.

  1. PaulDF

    PaulDF Second Unit

    Joined:
    May 17, 2002
    Messages:
    354
    Likes Received:
    0
    What is sonotube made out of? Seems to me it would just be compressed paper, like really hard cardboard. I have infinite access to sheets of this, and of varying thickness. Would 1-1.5 inches thick be good? Would that reduce the amount of bracing needed?
     
  2. JeffTodd

    JeffTodd Stunt Coordinator

    Joined:
    Jan 28, 2002
    Messages:
    200
    Likes Received:
    0
    Paul,

    I am by far not an expert in this area, but here is my $.02.

    Sonotube (concrete form) is about .25" thick from what I have seen. And from what I have read on this board it seems that the popularity of the sonotube subs comes from ease of build as opposed to box types. This ease of build is due to the cylindrical shape of the tube which naturally does not require as much bracing as a cube (the physics of this is beyond me, but the answer is easily found in searches on the topic I am sure). If you were to assemble a cube sub out of sheets of compressed paper, then I would think that you would need as much bracing or more than a traditional cube sub made from MDF.

    Hope this helps.
     
  3. Jack Gilvey

    Jack Gilvey Producer

    Joined:
    Mar 13, 1999
    Messages:
    4,948
    Likes Received:
    0
    The reason that such a seemingly insubstantial thickness of cardboard such as that in a Sonotube can work well in this purpose is precisely due to its shape. Tough to say if it would work well flat in a cube, although I'd guess anything could work if it was thick enough.
     
  4. PaulDF

    PaulDF Second Unit

    Joined:
    May 17, 2002
    Messages:
    354
    Likes Received:
    0
    I understand how a cylindrical shape is sturdier than a box made out of flat panels. No problem there. Let me clarify my question into two parts....
    1. Would an enclosure made of highly compressed paper (my best guess as to the construction of this stuff) be suited well enough for a sub? I am not sure how sound waves interact with the walls. Do they bounce around or go straight through? (This is probably a severely stupid question, sorry).
    2. Would a thicker walled enclosure require less bracing? Would for example, MDF 1.5 inches thick require less bracing than .75 thick?
     
  5. Jon Torres

    Jon Torres Second Unit

    Joined:
    Dec 30, 2001
    Messages:
    288
    Likes Received:
    0
    My .02 regarding number 2. Yes, I believe thicker walls would require less bracing. Although, the enclosure might get heavy. My next sub will just be single walled w/ bracing.
     
  6. Greg Monfort

    Greg Monfort Supporting Actor

    Joined:
    May 30, 2000
    Messages:
    884
    Likes Received:
    0
    In a round pipe, the pressure is everywhere equally, ergo no bracing required. Wall thickness/bracing isn't an issue beyond being able to hold its shape, grabbing it, dropping it, compressing it top to bottom, etc.. Since sonotube, quikcrete, etc., tubes are designed to withstand the pressure of wet concrete, the acoustic pressures of LF reproduction is inconsequential by comparison.

    Now if the tube is big around and/or long enough, then standing waves will develop within the intended BW, so in these cases care must be taken to deal with them in the design stage for best performance.

    WRT sheets of compressed paper (wood pulp), anyone who has messed with those flat gray treated cardboard filing systems knows how rigid they can be, so if sealed up would make good speaker/sub cabs also with minimal bracing, but why bother, since wood looks better, etc..

    While acoustic ouput can go through transparent materials, normally what happens with a sub, etc., is the AC pressure of a WL makes the cab 'breathe', so it actually reproduces the WL in parallel, and out of phase to the driver's output, and why you want the cab's physical properties to keep this from happening in the speaker's intended BW. Also, if some the electrical power is driving the cab, then obviously it's not being converted into acoustic power, so efficiency suffers.

    Stiffness is a function of panel thickness, among other things, so all else being equal, yes, the thicker panel will require less bracing.

    GM
     
  7. Hank Frankenberg

    Hank Frankenberg Cinematographer

    Joined:
    Oct 13, 1998
    Messages:
    2,573
    Likes Received:
    0
    Yes, strength of a cylinder far greater than a box. Some people attach a brace between the inside end caps of their sonosubs, which makes a lot of sense to me since the ends are, in reality, panels like the sides of a box.
    I'll stir things up a bit and say that IMHO, panel dimensions are a much larger factor than panel thickness in determining the need for bracing. I build very small enclosures for 3" full-range drivers with 1/2" MDF and they don't need/benefit from bracing. But a large cabinet with 1 1/2" thick ply/MDF walls needs bracing. Note that I'm not saying that thickness isn't a factor.
     
  8. Greg Monfort

    Greg Monfort Supporting Actor

    Joined:
    May 30, 2000
    Messages:
    884
    Likes Received:
    0
    >Some people attach a brace between the inside end caps of their sonosubs, which makes a lot of sense to me since the ends are, in reality, panels like the sides of a box.
    ====
    If the dims are I'll stir things up a bit and say that IMHO, panel dimensions are a much larger factor than panel thickness in determining the need for bracing.
    ====
    Agreed, as is the panel material, just to step it up a notch. [​IMG]
    ====
    > I build very small enclosures for 3" full-range drivers with 1/2" MDF and they don't need/benefit from bracing.
    ====
    Hmm, actually, assuming Fb is >several hundred Hz, then in theory either a different material or thicker MDF needs to be used for best performance. Or liberally damp the inside of the cab, which is ~the same as using thicker material. A way to find out is to make an identical cab with no driver/vent opening, but one installed, and drive it with sine waves at whatever voltage peaks the speaker would normally see to hear how audible they are and to find out where any resonances are. Not a completely accurate test if the design is vented, but close enough to find the worst resonances, if any.
    ====
    > But a large cabinet with 1 1/2" thick ply/MDF walls needs bracing. Note that I'm not saying that thickness isn't a factor.
    ====
    Right, simple box design cabs that are acoustically large WRT their intended BW need to either be inches thick or liberally braced in all dimensions for best performance. Being relatively weak, lazy, and always having plenty of scrap laying around, I use the thinnest, stiffest practical material available and liberally brace it.
    I even built a prototype decades ago using aircraft construction techniques out of balsa wood scraps left over from my model airplane building days after seeing the then new Lotus 25 monocoque GP racer perform so well, just to satisfy my curiosity. The concept was so obvious, it took an 'inventor' to see it. Performance was only as good as the amount of bracing used, and when finally done looked ~like a Lotus chassis on steroids, but performed right up there with the stainless steel cabs I did in later on.
    GM
     

Share This Page