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Some speakerbuilding Q´s

Discussion in 'Amps and Cabs [BG]' started by jock, Mar 12, 2005.


  1. jock

    jock

    Jun 7, 2000
    Stockholm, Sweden
    1. If you where to build a 2x12" box would it be any advantage to make it into two separate 1x12" cabs inside the box? I´ve read somewhere that the drivers would affect eachother negatively if they where in the same box.
    This box within a box would probably make the cab really stable and more bracing might not be necesary.

    2. Is there a thumb rule for how shallow a cab can be made? HiFi cabs are often really deep compared to the baffle width.

    3. Is there any negative effect if using pine plywood instead of birch ply? The pine is much lighter and would be great on my back. Does the pine ply have to be thicker and therefore weigh as much as the thinner birch to be as stable?
     
  2. The Clap

    The Clap

    Jan 5, 2004
    Scottsdale, AZ
    It doesn't hurt to have them in the same airspace, but the bracing effect can be useful.

    You may be tempted to build a shallow cab, but for a 2x12 you're probably going to need a relatively deep width for optimum box volume, but that depends. Standing waves are the issue, but that's something I don't know much about, and you can find a ton of information on if you look it up.


    Well, are you asking about different types of plywood materia or thicker wood?

    If A) Lighter wood is usually the sort of wood you're after, unless it's lighter for a reason that would make it weaker, such as a 1/2" width or bad wood. I don't know much about different kinds of wood though, so I can't say for certain.

    If B) Use 3/4" wood for speaker enclosures that do bassy duties (a no brainer for bassists, essentially).
     
  3. jock

    jock

    Jun 7, 2000
    Stockholm, Sweden
    Thanks.

    The question about the plywood was if it´s much better to use birch ply than pine ply? The pine is much lighter but I dont know if it´s less stable. :meh:
     
  4. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Q1:- Provided the speakers are the same, and therefore producing the same frequencies, there's no reason to give each speaker it's own cab. Indeed a single cab is often easier because you don't have to port each cab, so one port will do.

    Q2:- Try to avoid anything that resembles a cube. I've found that the cab dimensions are largely determined by the phiysical size of the components, especially height and width. The cab has to be at least as wide as the 12" driver right. It also has to be as high as the 2x12" + horn combined right? The only thing left is depth. Adjust the depth until the box has the right internal volume for that speaker.

    Q3:- I used Pine Ply on most of my cabs! In theory it's not as dense as Birch or MDF but, Birch ply is not readily available over here and MDF is like wooden condrete, it weighs a tonne.

    Brace the front baffle every time. If you have any longer panels which might flex under load, use bracing to stiffen them. I test this by standing on the cab and seeing if my weight can cause any of the panels to bend. If so, I brace - easy.
     
  5. I've found a few advantages for 2x specifically for slot porting.

    Let use an example of the Omega Pro 12. The SBB4 volume for this driver is net 1.23 cubic feet tuned at 39 Hz.

    I use full width slot ports with a baffle panel width of about 13" based on the diameter of the 12" driver. The required slot (inches) is 0.96H x 13.0W. The aspect ratio is 13.48 to 1, which is much higher than my personal limit of 8:1. This makes for a skinny, wide slot. These are reported to have turbulence problems, etc, so I avoid them entirely. Ratios up to 12:1 are supposed to work, but I use a self-imposed limit of 8:1 just to be sure.

    Using two drivers in a 2x cab requires doubling the internal volume of the cab. The tuning stays the same, but due to the increased volume, the required slot is now 1.9H x 13.0W, or an aspect ratio of 6.84 to 1.

    The downside to the 2x12 arrangement is the increased weight. Each Omega Pro 12 is just under 25 pounds, so you are lugging 50 pounds in drivers alone. Add in wood, screws, grille, dish, jack, handles, and it is a heavy beast.

    Another advantage of a 2x arrangement is series/parallel switching. Using a heavy duty switch in the jack plate, the 2x can be impedance-switched easily. A pair of 1x requires an external device to handle switching.
     
  6. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Bruce I agree about the portabiity of 2 small cabs, but sometimes you want to do one less trip to the car. I'm thinking in particular about my regular Sunday gig which is on the 3rd floor of a building with no lifts. And Sydney if full of venues with crappy load in/out setups.

    Get 12's with neo magnets, and use pine ply to save weight. Jock If you're patient, maybe wait and see if my 2x12 Beyma neo cab turns out. On paper it should be a small, lightweight, and very capable 2x12. It's a shame the first 12" arrive damaged - I would probably be close to finishing it by now if all went accoring to plan................oh well :(
     
  7. Bigwan

    Bigwan

    Feb 22, 2002
    Ballymena (hey)
    I remember asking Joris this question a few years back (where did he go to, by the way? Anybody hear from him lately?). The only really negative thing about having 2 drivers in the same space, other than what bgavin has pointed out, is that if you shag one of them the other will not operate correctly as it'll effectively be in a box twice the size that it likes...
     
  8. jock

    jock

    Jun 7, 2000
    Stockholm, Sweden
    Thanks guys.
    This project will probably have to wait as I´ve got some bills to pay.
    Please let us know how your 2x12 Beyma project goes, Petebass! Beyma is no 1 on my list right now. I´ve been looking at borh the 12LW30/N and the 112NdW

    (I remember Joris. I learnt a lot from him. Haven´t seen him onboard here for quite some time. Damn, I´ve been registered here for almoust 5 years now. Time flies. :eek: )
     
  9. SirPoonga

    SirPoonga

    Jan 18, 2005
    Q2) Play around with WinISD. A box with dimension according to the golden ratio is usually the best. Also if you cut the volume exactly in half you generally get good responses.

    However, I have to point out, avatar speaker cabinets cost not much more than what you could build them for. Once you price out the carpet, screws, edge protectors, jack plate, handles, wood, driver, tweeter, crossover...

    Another option is to build one of the Tuba24 or DR250
    http://www.billfitzmaurice.com/plan..._id/3?osCsid=d0e2eb1f990922f0c30a9087d97cddb1
    The creator of that runs his bass through the DR250a if I remember reading the forums correctly.
     
  10. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Avatar don't ship outside the USA. And even if they did, where's the fun in that :)
     
  11. jock

    jock

    Jun 7, 2000
    Stockholm, Sweden
    I´ve bought the plans for both the Tuba 24 and the DR250.
    The tuba is too big for me and the DR250 is too complicated for me to build. I got quoted $600 to have one built by a local carpenter. I don´t think so. :spit:
     
  12. I bought the plans for the AutoTuba, Tuba24, Tuba30/36, and will be building a set of Tuba36 Slim shortly.

    I have a number of 15" drivers laying around in boxes right now, and they are looking for homes in Tuba36 horns. I'll run some of my Rockford subs there too, just to see how they work out.

    I also scored (4) Alpha 6 drivers from an eBay firesale. They are going into a 4x vertical array and paired with Omega Pro 12s.

    My contract at Intel is up 3/31/05, so I'm cutting back to 40 hours a week, and will have free time for house repairs and cabinet building again. Building weather has arrived again here in Sacramento.
     
  13. jock

    jock

    Jun 7, 2000
    Stockholm, Sweden
    Cool. Let us know how it turns out!
    No DR250 for you then?
     
  14. I have more pressing needs for PA subs right now.

    I figure three Tuba36 Slims with a 24" width will have sufficient mouth area to produce dead flat to 55 Hz. This will cover the kick drum, and most of the 4-string bass range.

    We are currently running two JBL 1x15 + horn for mains. If I have spare time, the DR250a could be another project. I really need the PA boost in the 125 to 800 Hz range, which is below where the JBL 2345 horns cut in.