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Custom cab design questions

Discussion in 'Amps [BG]' started by Precisionb87, Jan 23, 2014.


  1. Precisionb87

    Precisionb87

    Joined:
    Dec 15, 2010
    Location:
    Philadelphia, PA
    Hello everyone.
    I am planing on building a custom 2-12 bass cab. I am an experienced cabinet maker, so I not worried there. I just need to figure out what volume (cubic feet) and port dimensions I will need to make it for best (or close to best) performance.

    The drivers I am using are these:
    http://www.tubesandmore.com/products/P-A-S12K3-8

    I have tried using a couple different free cab calculator programs, but they are giving me a cab volume of about 50 cubic feet, and port lengths of 1000 feet :eek: That can't be right...right?

    Could somebody with a little more brains help me out? :help:
    I though I just had to "tune" the cab to the free air resonance of the drivers. That should be a piece of cake, but again, I have managed to confuse myself.
    Any help is greatly appreciated.
     
  2. Stumbo

    Stumbo Wherever you go, there you are.

    Joined:
    Feb 11, 2008
    Location:
    Los Angeles
    Based on other cab plans or builds I've read about, usually the speaker manufacturer has some design specs you can get and work from.
     
  3. Mr. Foxen

    Mr. Foxen

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    Jul 24, 2009
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    Amp tinkerer at Ampstack
    Eminence speakers have cab plans on the website.
     
  4. swamp_bass

    swamp_bass I love it when a groove comes together Supporting Member

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    The box size I came up with was a wee smaller. I suspect your walk-in closet results were due to an English/Metric mistype in one of the parameters.

    [​IMG]
     
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  6. Precisionb87

    Precisionb87

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    Thanks Swamp. Is this for a 2-12? 1.24 cubic feet seems a little small.
     
  7. will33

    will33

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    That should be for a single 12, so, double it for 2 of them.
     
  8. will33

    will33

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    The curve looks nice, and I wouldn't want to raise tuning above 50hz if you play a 5-string, or even a downtuned 4-string, at least tuned down more than a half-step.

    1.24 cu.ft. ( 35 L ) per driver is already extremely small for a 12. Might have an issue trying to cram enough port in there to get the tuning low enough while keeping enough port area and still not letting it "unload".

    See what it does in something more like 1.5-2 cu.ft. per driver. Watch raising the tuning too high and/or letting the LF powerhandling get too low.

    You sure this thing shouldn't be in a sealed box going low like that in such a small space? Or is it something other than a Musical instrument or Pro Sound driver?
     
  9. will33

    will33

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    Ok, forget the sealed box thing. Medium Qts and EBP of 135.

    Is this an MI or PS driver?

    Something is just weird, assuming the above model & specs are correct.
     
  10. Precisionb87

    Precisionb87

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    I'm not sure I know what this means...
     
  11. Precisionb87

    Precisionb87

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    ...Ok, I'm just going to make the cab about 4 cubic feet unless anybody has any objections. Any advice on port dimension?
     
  12. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Gold Supporting Member

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    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    That's a nice woofer.

    I suggest four 4" diameter ports, each 12" long. This will tune the cab to the upper 40's and give you plenty of cross-sectional area for good airflow.

    If those ports are too long, an alternative would be three 4" diameter ports, each about 7.5" long. You should still be in good shape as far as airflow.

    If for whatever reason those ports are too long, you can do two 4" diameter ports, but cut the ends that go inside the cab at a 45 degree angle. Length should be 3.5", measured on the centerline. By cutting the inner end on an angle like that we increase the cross-sectional area at the opening, which facilitates good airflow (the front end doesn't need this sort of help because it will be flush-mounted, and that geometry facilitates airflow). Here's a thread where this port geometry is illustrated:

    http://www.talkbass.com/forum/f15/general-rule-2x12-sealed-cab-1034379/ -> I know it says "sealed" but it turned into a vented cab; see photos at bottom of second page.

    All of these port lengths assume 4.0 cubic feet internal volume before subtracting for the volume occupied by woofers and ports. In other words, they're based on 4.0 cubic feet gross internal volume.
     
  13. Precisionb87

    Precisionb87

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    Thanks for the input DukeLeJeune!
    How about just two ports? What port dimensions would I need?
     
  14. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Gold Supporting Member

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    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    You're quite welcome. Let me know if this is unclear:

     
  15. Precisionb87

    Precisionb87

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    Sorry, I read that wrong. Got it! I'll post pics when it's finished.
     
  16. Precisionb87

    Precisionb87

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    Dec 15, 2010
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    A quick pick of front view. Ports look a little big, but I guess I'll put it together and see how it sounds...
     

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