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bgavin/pm - Ply vs MDF question

Discussion in 'Amps and Cabs [BG]' started by patrickj, Apr 2, 2003.


  1. patrickj

    patrickj

    Aug 13, 2001
    Baltimore, MD
    I tried to send this to you via PM, but you have that disabled.

    --

    Hey, I've got a question that is probably suited to your expertise in cabinet construction.

    I'm in the thinking stages of building something equivalent to 2 SWR Triads (1x15+1x10+tweet) in one enclosure (properly tuned, seperate compartments per 'triad', etc).

    My first stage quality cabinets i built were 3/4" ply with a serious amount of (1.5x3 studs) bracing. You've mentioned that you have used MDF for some of your cabinets, and wondering if you would suggest MDF for my project.

    I'm not concerned about weight as I don't forsee this being carried anywhere. The enclosure will include tilt-back casters & handles (much like 810s now, etc) so it can be used like a dolly. MDF seems like a very dull/dead material in distributing vibrations as opposed to ply - unless you reinforce nearly the entire cab (bringing it to the weight of MDF) it'll buzz & vibrate.

    Would you recommend 3/4" MDF for this project? If so, do you have any tips on working with it (glues, screws, etc)?

    --

    That being said, does anyone here have any suggestions/comments?
     
  2. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    I have used Plywood on all my projects, despite it being less sonically stable than MDF, purely because weight is a big part of my design criteria.

    However, if weight is not an issue, than MDF is probably the way to go.

    Simple butt joints work fine. Use plenty of timber advesive and screws to hold it all together. I also use a few long clamps to hold it all tight while it's drying to create an airtight join.

    MDf and plywood both chip away when you accidentally bump them into things, so a protective covering is also a good idea.
     
  3. MDF is heavy, dimensionally stable, and sonically inert. Void-free plywood (Baltic Birch, Apple-Ply) is lighter and more prone to vibration.

    All the commercial cabs are plywood. Properly braced plywood should do the job for you just fine. I understand Eden makes their cabs out of 5/8" plywood, but the XLT series is heavily braced. The top and bottom ports are ingenious in the way they brace those two cabinet walls.

    A simple 3/4" square cleat or two on a panel will go a long way toward reducing buzzing. You can run a brace between these cleats on opposite walls for extra rigidity. I do an X-Y-Z plane bracing system that connects all opposite walls to a common junction in the center of the cab. This is anal and labor intensive.

    I cannot sit on my 3/4" MDF sub cabinets at full volume. The vibration numbs my butt cheeks in a few minutes. Very uncomfortable.

    :D

    I use butt joints reinforced with 3/4" square cleating that runs the full length of each joint. This is a labor intensive technique but it provides significant glue + screw area for each panel. Joints are glued with TiteBond-II and caulked with Silicone-II sealant. I use iridium coated wood screws and counter-sink every screw hole. I clamp the entire cabinet together dry, then drill all the screw pilot holes and install the screws. This is extra work, but makes the job go much easier when assembling the joints with glue.

    I use a 3/4" round router bit to round all corners. My two subwoofer cabs are uncovered MDF and have taken a beating consistent with two full years of 2x weekly gigging. I left them uncovered so I could see how the joints held up over time. Nothing has come loose.

    Pickup truck bed liner is reputed to be the hot thing in coverings. It is pretty indestructible, but is expensive to apply in small quantities. If you have many cabs to shoot at once, the price is better.

    I would not build this project as a single cabinet. The panels will be very large and prone to significant vibration. You didn't mention which 15" driver, but nearly all of them require a good amount of cabinet volume for proper tuning.

    I go the other way and build everything as separates for smaller individual size, ease of handling, and more rigid structure. I'd put the 15" in a separate cab, and the 10" + Tweeter in a second cab that sits on top. Put the crossover network in the 10" cab and provide for an interconnect between the two cabs. I use Speakon cables for this. I also use a two-jack dish for double Speakon input connectors so I can daisy chain to a second set of cabs.
     
  4. bino

    bino

    Jun 27, 2002
    Orange County
    Anyone with experience using 1/2" MDF? I ask only because that is what is used in the Rx Dr. Bass cabs and actually weighs less than their birch ply cabs. And does "sonically inert" refer to something good when building bass cabs?
     
  5. patrickj

    patrickj

    Aug 13, 2001
    Baltimore, MD
    Opps nm! :ninja:
     
  6. Sonically inert is desirable. Those who tell you the panels produce musical vibrations are blowing smoke up your ass. This is cabinet coloration and very unwanted. Worse, it absorbs and wastes acoustic power that is better used for making bass.

    Buzzing for cabs is a bad thing. Use buzzing for marital aids.

    I use MDF for everything because it is dimensionally stable. Plywood (non marine) generally sux. I make racks, micro cabs, and horn enclosures from 1/2" MDF and it works fine. Heavier than 1/2" baltic birch ply, but nowhere close to as expensive. For built-ins, such as club subwoofers, 1" MDF is worthwhile.

    I use regular ol' TiteBond glue. There are some exotics also, but this works great for me. I hauled my subs all over everywhere and the joints stay put. I use butt joints, with full cleating, glued + screwed on 6 to 12 inch centers. Cleats are MDF cut as 3/4 x 3/4 and run the length of the joint. Be sure to silicone seal after building, and BEFORE installing the speaker. The fumes will EAT ALIVE a foam cone surround.

    The Triad thing is going to be big, if properly enclosed and tuned. I build separates, but mine are for portable use, and I'm an old fart with a back still in good condition. Separates are much easier to negotiate stairs.
     
  7. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL
    Half is a bit too thin. You will want to stick to 3/4 and brace if need be on long panels. I mean, you can brace the 1/2, but it will be a lot of joints and screws and stuff. Sonically Inert means that it is not likely to color the sound by resonating when the speaker gets moving. And that is definitely a good thing when building bass cabs especially.
     
  8. bino

    bino

    Jun 27, 2002
    Orange County
    Would the problem of adding all the extra bracing have a negative affect on the sound? Or is the main issue with such thin MDF be with its durability?
     
  9. notanaggie

    notanaggie Guest

    Sep 30, 2003
    MDF chips like heck if thick, and shatters if thin. It is stronger than particle board, if that matters. Terrible for any kind of impact, and the thinner the worse.

    With it being heavy, impact is more likely. Someone once made powered monitors out of it, might have been the old Audio-Centron brand. Anyhow they pretty much all broke in use, and that was 3/4 inch MDF.

    But almost any plywood is far better for durability. OSB, or even some kinds of non-oriented chipboard are somewhat more durable.

    The slickest I have seen was a sandwich, with ply for strength, and MDF for sonic deadness. Never did find out how that worked, but it appeared to be a good idea.
    The folks that had it were at NAMM years ago. I think it was "Joe's Sound and Salami" , but might have been others, I don't recall for sure.

    I think whoever it was had a video of the cabinet being towed through an alley on a chain, crashing into dumpsters, etc. Came through scarred but in one piece.