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Designing a bass cab - looking for input

Discussion in 'Amps [BG]' started by M0ses, Feb 6, 2014.


  1. M0ses

    M0ses

    Joined:
    Sep 11, 2009
    Location:
    Eastern Wisconsin
    I'm not an expert by any means, but I have done a lot of reading research, I know the basics, and hopefully I'm not wildly off base here. Experts, please chime in and tell me how wrong I am.

    Goals
    - Small size: I'm going on tour and the smaller I can make my gear loadout, the better.
    - Lightweight. This should come with the small size and neo drivers.
    - Widest dispersion of mid and hi range frequencies as possible. This cab will essentially only serve as a bass monitor for the drummer and I. I will be going through a sufficient PA at all venues on tour. I use a VERY mid heavy tone.
    - Minimize problems like comb filtering and beaming.

    Things that are not goals
    - ALL THE BASS MUD
    - ALL THE SPL


    So. Here's what I'm thinking. (Please note, I haven't drawn anything to scale yet.)
    The cab will be a prism, with this shape as the base.
    [​IMG]
    It will be 36 inches tall, bringing the internal volume to 3752.6 in cubed.

    It will be loaded with twelve of THESE in a 2x6 line array. Modeling those drivers in WinISD with that volume gives me this:[​IMG]
    Which looks like bass response I can live with. I use a HPF set somewhere around 50Hz.

    They'll be crossfiring, 50 degrees off-axis. Assuming a 1/8in protrusion (I don't have the drivers in hand yet), if I've calculated everything correctly, I can mount them .06in away from the corner. This number seems ridiculously small but if I've made an error, I can't find it.
    Now, I'm not entirely sure which point on the speaker I need to calculate point source spacing from when the drivers are not on the same plane. I used the plane of the baffle at the center of the driver for these calculations, leaving me with a horizontal spacing of 4.66in.
    [​IMG]

    There will be 3 inches at the bottom for ports. I've been unable to find really helpful information for figuring out how to do them. WinISD tells me I could do four 2in diameter ports .69in long for that tuning. Those would end up being cross fired as well, of course. ANY advice on this particular subject would be much appreciate.

    The cab will be wired to 5.33 ohm and will be able to handle 300W RMS, which is just about what my amp is going to throw at it.

    So again, please, tell me all the ways this is a terrible idea. I'm too worried that I'm actually totally clueless to drop the money on the drivers.
     
  2. rogypop

    rogypop

    Joined:
    Jan 10, 2009
    Location:
    Croatia
    Those drivers have less than 2mm xmax so what you are going to get is largish cab with zero lows. Not to forget to mention is some kind of high pass filter you would have to use,without it you would toast your drivers, especially with 80 hz tuning.
    if you like loads of mids bill fitzmaurice's jack 12might be the right cab for you. Check it out.
     
  3. M0ses

    M0ses

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    Sep 11, 2009
    Location:
    Eastern Wisconsin
    They're spec'd to 95Hz, and are -3db at 80Hz with that tuning. They're supposed to be full range. I don't have the exact figures for cone surface area but a quick approximation shows significantly more surface area than a single fifteen.

    I wouldn't classify a cab that fits into a 12x12x36 box as largish. Kinda tall but very thin, easy to lay down in the back of your car.
     
  4. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Gold Supporting Member

    Joined:
    Nov 24, 2008
    Location:
    Preston, Idaho
    Disclosures:
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    So M0ses, you go up on the mountain, and that's what you come down with?

    Who you been talkin' to??

    Seriously, that's a very interesting design. Mike Arnopol uses cross-firing drivers in most of his Big E cabs, and in the room behind me as I type is a halfway-finished cab that combines cross-firing mids with a big woofer.

    You asked about how to calculate point source spacing... a splayed array does not act like a point source. The radiation patterns criss-cross, giving you a considerably wider pattern up to short enough wavelengths where the array elements are beaming considerably, at which point the net pattern becomes two-pronged with a hole in the middle. In this case, the hole in the middle won't develop until we get to about 8 kHz. Your effective net pattern width up to 6 kHz is about 100 degrees.

    So in other words, very nice job on the box design.

    Now, you mentioned that you use a VERY mid-heavy tone. Eyeballing the curve, I wouldn't call that speaker "mid heavy" - its region of emphasis is from 2 kHz to just north of 10 kHz, and I'd call all of that "treble". Unfortunately I don't know of a lightweight alternative offhand. So anyway if you use that speaker, might have to do some aggressive EQ-ing to reach your tone goals.

    I'm less concerned about the modest x-max because you already specified that high SPL isn't among your criteria, but a protective highpass filter would be a good idea.
     
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  6. M0ses

    M0ses

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    Thanks, guys, for the kind words and your evaluation. I'm just a crackpot with just enough engineering training to be dangerous who has read a lot on here and on the BFM forum and any articles I can find online. I probably need to be brought back down to earth. I see what you mean about the driver being pretty treble heavy. It's so hard to find the perfect driver for your needs. Why can't everyone just publish honest SPL charts?
    In your opinion, would these really need to be paired with a larger woofer and crossover to truly be a functional full range cab?
     
  7. will33

    will33

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    Playing with a middy tone and not needing to fill a room with the rig alone, I'd say no need for the sub. I would double-check your excursion chart just to see what it does just below the 80hz tuning frequency down to where your HPF cuts it off, just to be sure you can add some "oomph" via eq if you felt the need.

    Way cool cab, man.
     
  8. will33

    will33

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    I also haven't done the math as to where vertical dispersion might start to narrow considerably with 6 of those lined up, but a little tiltback wedge or leg might be in order if you're standing close to it.
     
  9. rogypop

    rogypop

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    Surface of the cone is just one part of the equation, what matters is displacement and you get it by multiplying xmax with surface of the cone. There are some ten, or even eights that displace more volume than 15. Mo displacement, mo lows! :) Thats just one parameter but important one though, especially for bass guitar. If you wish to roll your own, vertical 4x10 would do the trick, with enough dispersion and oomph which you can eq in or out, as the gig requires.
     
  10. M0ses

    M0ses

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    That does make a lot of sense.
     
  11. M0ses

    M0ses

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    I haven't found an excursion chart for this driver. Or basically any drivers.
     
  12. will33

    will33

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  13. M0ses

    M0ses

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    I've been using the basic version of WinISD. Downloading now...
    Also those Dayton drivers looks pretty powerful, but more than twice as heavy. I'll model them and see if they're amazing enough to outweigh ;)
     
  14. Cirk

    Cirk

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    Just brainstorming, but how about a ported cab using a nice 10 or 12 inch neo woofer crossed over with 2 cross firing mids? Think that might work for you?
     
  15. M0ses

    M0ses

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    I'm having trouble plotting the Dayton driver because WinISD is telling me the Q values listed are inconsistent.

    I have avoided mixing driver sizes for a few reasons. The big ones end up taking up a LOT of space; if this cab gets any bigger, I'm going to have to split it in two. Which would be pretty necessary anyway because a larger driver or two aren't going to be crossfired so would need a box with a flat front face. I have no idea how to design crossovers, so that's a ton of added complexity, expense, etc. It's also a whole 'nother can of worms to get two speakers that match each other well, in terms of sensitivity, impedance, etc.

    I believe in the idea. If Phil Jones can pull off small cones, I don't see why I can't. The specifics are most certainly up for debate, though.
     
  16. M0ses

    M0ses

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    Plus, the more I look at this model, the more I like it.


    [​IMG]
    The blue is my cab, the grey is a 4x10 loaded with Eminence Kapplites. The graph is (theoretical) SPL, not gain. Which means that, yes, the 5 cab is lagging behind in deep bass, but I don't like that sound anyway, and it's got this beautiful bump in the 100-250Hz that puts it ahead of the 10s, and is exactly what I'm looking for. Then, according to the driver's data sheet, it's got a pretty flat mid response and lots of treble, which is super easy to roll off.

    Still having trouble figuring out how to use the excursion chart though. It's just showing me a flatline 0, is that because I don't have enough relevant parameters entered?
     
  17. will33

    will33

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    Under the tab labeled "Signal", the power input defaults to 1 watt. Enter, say, 200 watts there and the excursion chart will jump up, reflecting the power increase. Fish around with the power input until the excursion reaches the drivers xmax. That is theoretically how much clean bass output it could make, IF we were playing sinewaves. At that point, I like to make sure the port air velocity is 20 m/sec or less. If not, increase port area, or at least use flared ports, they can get away with a little higher air velocity without chuffing, say somewhere in the high 20's m/sec. Those are just general guidlines, not hard and fast rules. More like how small of port area you can get away with.

    If you're using Alpha Pro, you can also set eq curves, to see how it behaves with your more rolled off bass..
     
  18. M0ses

    M0ses

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  19. M0ses

    M0ses

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    The cone excursion graph is working for other cabinets.
     
  20. will33

    will33

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    You must be missing some specs or have a bug in the program.

    If you click on "parameters" at the bottom of the small driver window that is overlayed on the graph, it'll give you a drop down list of the driver specs. Double-click on each individual spec and you can edit them or enter missing ones. I'd just do that and enter all the specs as they are on Celestions datasheet for that driver.
     
  21. M0ses

    M0ses

    Joined:
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    Well I got the excursion chart to work. What a super handy little graph. It looks like rogypop was right. I can put 60W into this thing before it hits Xmax at 123Hz, so even the HPF at 70Hz doesn't solve that problem.

    Box design: cool.
    Driver: not up to the task.
    I'll look around for something that might work, but it might have to be back to the drawing board.
     

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