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Thread: bendable plywood any good for cabs?

  1. #1
    scorpio
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    bendable plywood any good for cabs?

    I'm building new bass enclosures and would like to give them a rounded shape similar to the B&W 800 series type. I would plan to use 3 or 4 layers of bendable plywood (sorry, I don't know if this is the correct technical term in English, it's direct translation from French). I would glue the sheets together using a very strong adhesive for floorboards that maintin some elastomeric quality when dried. Thing is, I don't know if this would make a 'good' cab or not, I don't see why it should not, but has anyone here attempted to make sharply curved cabinets, and if so, what did you use?

    Thanks,

  2. #2
    Senior Member richluvsound's Avatar
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    Hi Scorpio,

    the only flex ply I would use is designed for boat building . 3 x 6mm layers. Use epoxy or polyester resin.Use a cotton based filler powder with the resin to create a gap filling paste. You don't want any flex to the cabinet , too hard to tune ! . You will need stiffeners every 150mm , 200mm max.

    I will start making curved panels next week .I will start a thread. I dont think there is one yet. A JIG is a must.

    Rich

  3. #3
    Senior Member Hoerninger's Avatar
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    Quote Originally Posted by scorpio View Post
    ... , but has anyone here attempted to make sharply curved cabinets, and if so, what did you use?
    My local dealer has MDF with cuts from the back which can be bend easily.
    ___________
    Peter

  4. #4
    scorpio
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    Hi Hoerninger, I can get this type of MDF as well, do you know how sharp a radius you can make with this material? The plywood can make an 80 mm radius minimum, it's really very flexible. I was wondering if the MDF would not break along the kerf if bent too tight?

    It's going to be applied as several skins over a matrix-type frame, I have little concern about flex in the cabinet when done. I'll shoot pics as I go along, maybe someday will post them

    Cheers

  5. #5
    Administrator Robh3606's Avatar
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    You might want to PM Widget. He has used a similar material and may be able to help you out.

    Rob

  6. #6
    Senior Member grumpy's Avatar
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    some good reading here too:

    http://www.neatconcepts.com/

    4-6" minimum radius (1/4" Neatform) - MDF
    6-8" min rad (3/8" Neatform) - MDF
    12" min radius (3/4 Neatflex) MDF + bending birch plywood

  7. #7
    Moderator hjames's Avatar
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    Buncha folks have done work with this concept in the past -
    John W, Widget and a couple of other projects I read about but can't find right away ...

    Search this site for "bondo", "kerf", and other similar keywords to see what floats up from a few years ago!

    Some of the work looks similar to the danish style TiK series - very cool!


    http://audioheritage.org/vbulletin/s...t=bondo&page=3
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    And some information on how a commercial product with curved sides was made can be read on the TAD / Pioneer website (M1 reference monitor) and in the owners manual / literature cut sheet for Pass Labs "Rushmore" loudspeaker.

    TAD did a a very nice translam and Pass Labs a laminar bend. From the text, Nelson Pass used 17 layers of an engineering grade wood like aircraft / marine spruce in building his cabinets. TAD stacked up piles of Baltic Ply with generous through bolts and hard glue.

    From personal experience the TAD cabinet was more sonically "dead" via the knuckle test.

    Cyclotronuy

  9. #9
    Senior Member edgewound's Avatar
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    The latest TAD Reference One is made up of layers of thin MDF to build up the enclosure.

    The designer, Andrew Jones, told me that they had problems with the stacked laminated plywood.
    Edgewound...JBL Pro Authorized...since 1988
    Upland Loudspeaker Service, Upland, CA

  10. #10
    RIP 2011 Zilch's Avatar
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    The key to making the kerfed MDF work is filling in the voids. That's what I concluded from Mr. Widget's experiments with building curved cabinets.

    My own approach would be to fill them with structural adhesive as part of the forming process.

    I agree its elastomeric properties would be a significant resonance-dampening element in this.

  11. #11
    RE: Member when? subwoof's Avatar
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    bend me, shake me, anyway you...

    There is a type of plywood that is Luan ( generic mahogany ) that all the layers are grained in the *same* direction. I used some for a customers project and even the 3/4 inch stuff was bendable within reason.

    But it was a real pain to transport + shuffle around the shop ( floppy ) and that stuff smells like a wet fart when sawed......you would need to seal both sides very well..



    sub

  12. #12
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    Quote Originally Posted by edgewound View Post
    The latest TAD Reference One is made up of layers of thin MDF to build up the enclosure.

    The designer, Andrew Jones, told me that they had problems with the stacked laminated plywood.
    Hi Edgewound,

    do you know if they are still building up from the ground using CNC'ed sections or have they gone to a more conventional construction following the delamination issues?

  13. #13
    Senior Member Storm's Avatar
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    Reading this thread made me think of something.

    Isn't there veneer that I could get to re-do the 250TI's in like a rosewood or something?

    Would it be difficult, seeing that the corners are smooth?



    FWIW: The 250TIs are listed for one more go around. Offers are more than welcome.

    Thank you.

    -Storm.

  14. #14
    Senior Member edgewound's Avatar
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    Quote Originally Posted by merlin View Post
    Hi Edgewound,

    do you know if they are still building up from the ground using CNC'ed sections or have they gone to a more conventional construction following the delamination issues?

    Hi Merlin,

    They are using thin layers of MDF to build up the curved back and side profile.

    The MDF layers are glue laminated together. A result of stressed panels(bent) is that they don't resonate. That's some science used by old aeroplane builders...curved wing surfaces makes a more rigid airfoil.
    Edgewound...JBL Pro Authorized...since 1988
    Upland Loudspeaker Service, Upland, CA

  15. #15
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    TAD M1

    I've spent quite a bit of time with the original TAD M1's, most of the US pairs (no commercial affiliation or interest, just friends with the major US seller)... they did not delaminate.

    When you have end-grain, and not, hard glue and not then sanding for a perfectly smooth finish across all the different surfaces is difficult at best. Sanding wears away the softer wood quickly and affects the hard glue least. As one might easily imagine this quickly leads to a washboard finish unless one is very, very careful.

    OK, lets presume Andrew got the finish perfect at the factory... and I'm pretty sure he did. Now you take that cabinet, cycle it through hot and cold, damp and dry (think wood and up to 18% growth possible on something like cherry with extremes of climate, most of it in one direction btw). What you quickly discover is that the "perfect finish" is only perfect under one enviornmental condition.

    Out in the real world the finish began to show stresses and the differences in enviornmental expanison could be seen... the cabinets failed in a cosmetic sense, not to the best of my knowledge a physical sense.

    Cyclotronguy

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