Where to find 1.5" thick MDF?

Discussion in 'Archived Threads 2001-2004' started by Mark Hayenga, Mar 25, 2001.

  1. Mark Hayenga

    Mark Hayenga Supporting Actor

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    Hey guys,
    I'm starting to think about a new sub for myself. The last one I built I made with two 3/4" layers laminated together, but it was a pain to do the lamination. Does anybody know of a good source for 1.5" thick MDF? TIA,
    Mark
     
  2. Jeff Rosz

    Jeff Rosz Second Unit

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    hello mark,
    that would save alot of time. but, i have never seen it anywhere nor have i seen 1" stuff. but the 1" exsists because im sure you've seen kits using 1". but think about this...it kinda goes without saying but, how would you handle a 1.5" sheet of this stuff?....it would weigh a ton.
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    *why build one when you can build two for twice the price*
    jeff
     
  3. Bob Sorel

    Bob Sorel Stunt Coordinator

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    I had the same problem. The solution for me was to buy 3/4" sheets at Home Depot for $15.95 each, and have them cut it into quarter sheets right there (which they did for free, and it is a lot cheaper than buying their ready made quarter sheets [​IMG] ). Then I laminated the quarter sheets at home, which was not a problem at all, and only required 6 C-clamps. This left me with units that were easily manageable, yet very solidly constructed. Of course, if you need pieces that are bigger than ~24"X48", then my idea goes out the window.
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  4. Chris Christensen

    Chris Christensen Auditioning

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    Mark: You might try some "Hardwood" retailers in your area. If you have a Paxton's, I know they carry 1". The thickest I have seen and used is 30mm (1-1/4") while I was in Iceland, but 1" is the thickest I've seen here. I agree with Bob, go to Home Depot, the 1" stuff through Paxton's is $48. Good luck!
     
  5. Pete Mazz

    Pete Mazz Supporting Actor

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    Mark,
    I've never seen MDF offered more than 1 1/4", and that was wholesale.
    As far as laminating 3/4" panels, you would get stiffer finished product than single 1 1/2". Easiest way I do it is to pre-cut manageable size pieces. Find a flat area of concrete floor. Get a foam roller cover and lay sheet down, pour some wood glue around and then roll out. Lay your top piece on and then the next bottom piece and keep stacking this way until you have them all glued. Then simply weigh down the whole pile with whatevers handy and heavy.
    One question though, I keep reading about using 3/4" baltic birch plywood for subs. Obviously you have a different take?
    Pete
     
  6. Jack Gilvey

    Jack Gilvey Producer

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  7. Greg Monfort

    Greg Monfort Supporting Actor

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    The goal in building a sub box is rigidity. The reason is twofold, first for best mechanical to acoustic transfer efficiency, and second, to raise its resonance beyond the sub's -24dB BW.
    Well braced 3/4" void free, or thicker, plywood such as Baltic Birch/Appleply/marine grade are the best cost-to-weight-to ease of construction performers IMO.
    There's more than one way to meet the goals though. 10ga cold rolled steel, or 1.25" thick MDF are ~functional equivalents.
    WRT bracing, an ME once told me that large panel areas of 3/4" marine ply should be broken up by triangulation until the various areas were < ~1ft^2. This would sufficiently raise and attenuate their resonance to the point where only a layer of R-19 fiberglass on one side wall, back, and top would be sufficient. He also noted that all sides should be coupled together, whether by horiz/vert shelf braces, or 2x4's, hardwood closet poles, whatever, for good acoustic efficiency. Since joints raise the resonance at that point, damping them can be problematic, so edge braces made from no-void ply, or metal angles (no MDF or softwoods!) should have gaps at junction points. Where edge, shelf, whatever bracing isn't practical, then doubling up ply panels is best.
    My experience has been that he was spot on.
    GM
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    Loud is beautiful, if it's clean
     
  8. Robin Smith

    Robin Smith Stunt Coordinator

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    I was at Home Depot today (in Canada) and they had 1" MDF. The price was good too (I thought). A 48" * 48" piece was CAN$19.34 (about US$12). They had smaller lengths too.
    So my obvious next question is, would one piece of 1" MDF on each end be enough for a 20" sonosub?
    Mark, what was such a pain about the lamination? I thought it was simply a well spread layer of wood glue and lots of pressure til it dries/sets???
    Did you cut the holes before or after laminating? I am getting ready to begin my Sonosub and am gathering info.
     
  9. Mark Hayenga

    Mark Hayenga Supporting Actor

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    Hi guys,
    Thanks for all the rec's. The only downside to the baltic birch is the price, I've only been able to find it in small sheets at the local WoodCraft, and it was outrageously priced. Looked great for subs, though...
    The problem I have with the lamination is that MDF is rarely perfectly flat, and I'm always worried about the lamination in the center (where I can't clamp large sheets). On the last sub I built I ended up using screws every 3" in both directions on the panel (ie lotsa screws). It worked very well (I routed the driver and port cutouts after lamination and there was a perfectly uniform, very thin glue line inbetween the boards with glue penetration shown in the cross section). But it was really time consuming...
    Oh well. I will let you guys know how the search goes. Thanks again,
    Mark
     
  10. Hank Frankenberg

    Hank Frankenberg Cinematographer

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    Mark, if you are glueing 4' x 4' pieces, why not do this: take two, spread your glue uniformly over one, slap the second on top, line them up and set aside. Glue two more together, line up, then line each glued pair up with a front wheel of your car. Lay large scrap pieces on top of each glued pair to aid weight distribution, then drive your car up on them. That should be enough weight on the center of each sandwich, plus some weight distribution. After 15 minutes or so, drive the car back off them. The glue will be fairly well set and you could then stack your sandwiches together and distribute weights around a top scrap board. Weights: barbell weights, concrete sacks, kitty litter sacks, gallon cans of paint, spare paper clips, etc.
    I've never tried this, but have thought about it and if I ever get rushed to prepare MDF or plywood sandwiches, I will try it. I've not had a problem with final-sized MDF panels. I've rarely seen a piece of plywood that was flat.
    BTW, did you go to the local meet Saturday? I was out of town. [​IMG]
     
  11. Christian Sonntag

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    Just a thought, but I would suspect you would want to laminate the 3/4" sheets using "glue" that would remain somewhat flexible, rather than hard drying. This would help in a couple of ways.
    First off, the differences in density and acoustic resonance would really aid in dampening internal vibrations.
    Also, the resulting structure would be less likely to vibrate apart or crack apart due to the glue cracking. This might result in a longer lasting, more stable unit.
    Hope this helps.
    Chris
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    Christian A. Sonntag
    "The world owes you nothing. Take responsibility for your own actions!"
     
  12. Jones_Rush

    Jones_Rush Stunt Coordinator

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    I can get my hands on a 1.2" thick MDF board for a great price. Do you think that 1.2" MDF all around is thick enough for a sub ?, Will it be better to use 2 3/4" MDF boards for the front baffle instead of only 1.2" ?
     
  13. Mark Hayenga

    Mark Hayenga Supporting Actor

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    Hey Hank!
    Nope, I didn't get to make it - school has me busy these days, and any free moment I get I spend speakerbuilding [​IMG] I've got my bookshelf speakers to +/- 1dB across most of their bandwidth now (predicted response). I plan on dragging one of the completed sets to a future meet so's I can get some opinions.
    Mark
    PS - I like the car idea
     
  14. Hank Frankenberg

    Hank Frankenberg Cinematographer

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    Mark: Picking up on Christian's thought about the glue acting is an interlayer vibration damper, you could sandwich a sheet of loaded vinyl damping material (the stuff that is sold to the custom car speaker installation folks - expensive, but Parts Express sells a generic version for far less$) between two layers of MDF. I use the damping material to line inside cabinet walls and have been thinking of doing the sandwich thing.
    BTW, I'd like to hear your new speakers and experience that +/- 1dB [​IMG]
     
  15. Mark Hayenga

    Mark Hayenga Supporting Actor

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    Interesting... what types of adhesives would be required with the sandwiched layer construction(ie MDF/loaded vinyl/MDF) ? Would contact cement do the trick? Scott has used Moyen damper to laminate MDF for midrange sub enclosures (which works really well) but I'm hesitant to use it on anything as large as a sub panel (and it'd be costly). The vinyl might just do the trick though...
    BTW, I'm in the labs on campus right now, but I'll email you a screenshot of the predicted response for the bookshelf speakers when I get home tonight. I'm using 6th order acoustic slopes on both tweeter & midbass, it's amazingly flat save for the crummy test cabinet's resonance at 330Hz, a diffraction effect at 3.5-4kHz, and this null thing that all Morel tweeters seem to do at 13.5kHz. Even with those it still fits in a +/-1dB window from 200Hz on up to 13.5kHz (haven't hassled Scott into measuring the nearfield woofer + port and summing them into the midbass response yet, but they f3 around 60Hz).
    Mark
     
  16. Hank Frankenberg

    Hank Frankenberg Cinematographer

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    The new polyurethane (expensive) glue might work, but I would do test pieces with good old, obnoxious (use in well-ventilated area) contact cement. Keep in mind that some of the old-timers (ThomasW for one, if memory serves me) say that you don't need the density of MDF for subs - they recommend void-free plywood (I know, lots more expensive than MDF). Also, the pros at Northcreek Music recommend for mains speaker cabinets, a sandwich of MDF outer layer and void-free plywood inner layer, with their proprietary glue, which doesn't dry rock-hard, as a sort of inter-layer resonance-difraction medium. I have some of their glue and it resembles and smells a lot like white craft glue. It would be a great project for someone to do some definitive (for us D-I-Yers) cabinet materials sandwich construction experiments/testing to determine the best method for mains and subwoofer wood cabinet construction. I bet there have been such articles in Speaker Builder (like the recent one on cabinet SHAPE experiments).
    6th order? What's the parts count on those puppies?
     

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