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DIY cab to as extension for GK MB150

Discussion in 'Amps and Cabs [BG]' started by snowdan, May 15, 2006.

  1. snowdan


    Feb 27, 2006
    sorry for the screwed thread title! can't change it.

    so there's my question: i want to bulid an extension cab for my GK MB150.

    i want it to be quite compact, low budget but good quality. the GK obviously lacks lows in the longer range, so it will have to be a fair bit bigger than the GK. i was thinking about the size of a SWR WM10 cab but wider, then put on it's side. the result would be a rather high cab, a tad wider than the GK and way deeper.

    my questions:

    sealed vs. ported? my intuition says sealed.

    speaker? it'll have to be a single speaker or two cheap ones. cost is an issue.

    i was thinking 1x10, 2x10 or 1x12. leaning towards 1x12.

    i will use it for DB on bigger stages and in th elong run for GB (6 string) in medium loud settings.

    from the eminence range, which 12 ist the best buy?

    i can ie get a beta 12 for 55 euros. it seems to have a good Xmax.

    i don't need extreme power handling, it will only have to cope with 100 watts or so from the GK.

    will a beta 12 in a sealed box sound good?

    are there as cheap or cheaper speakers i should take into consideration?
  2. snowdan


    Feb 27, 2006
    also of interest: which cabs are the MB users here using as extensions?
  3. snowdan


    Feb 27, 2006
  4. Eric Cioe

    Eric Cioe

    Jun 4, 2001
    Missoula, MT
    I'm getting a Low Down Sound neo 1x8 3-way on Friday, and I'll be using it with my GK 200MB (same amp but older). I'll let you know how it goes.

    And bump!
  5. 62bass


    Apr 3, 2005
    I used the MB 150 with an Eden 1-10 once. It added quite a bit to the output and bottom end. i didn't care for the horn tweeter on the Eden and turned it way down. However, I think i'd go with a sealed 1-12 to more closely match the characteristics of the existing combo amp's speaker.

    Probably Eminence is your best bet because they have such a wide range of models. Someone here should be able to give you the best choice and cabinet size.
  6. In my opinion, if you're looking for low end extension, build a front-ported 1x12 using an Eminence Neodymium 12" speaker. Lightweight, and you'll be able to make it a reasonable size.
  7. Petebass


    Dec 22, 2002
    QLD Australia
    The trouble is the Eminence Neo 12 doesn't go all that low. Tonally you'd be happier with a Delta 12LF which is widely regarded as quite deep for a 12.
  8. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Check my web page for the response curve of the MB150, then model the new Eminence neo 12 into a 30 liter box with 45 Hz port. Very nearly the same curve, but considerably higher sensitivity.

    Otherwise, for more low end, like Petebass says, the Delta 12LF is a good choice.
  9. snowdan


    Feb 27, 2006
    i just looked for the delta 12LF. seems to have low sensitivity, uh?

    94,5 as stated by an ebay seller.

    but i think the lower my speaker sounds, th eless bass EQ i need in the GK, which the internal will thank for.
  10. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    That figure is meaningless, as it's a broadband spec that doesn't tell you what the driver does down low where it counts. The way to get a meaningful comparison is to download WinISD (linearteam.org) and run comparison simulations to see what different drivers do in the box size you're considering, and with the Alpha version also compare xmax/power considerations. If you do so you'll find that the Delta 12LF is one of the best choices available, not only with regard to sensitivity below 100 Hz, where it counts, but also for having adequate xmax for high output.
  11. I would do the Delta 12LF in Flat (3.97 cubic feet, Fb=43, F3=41).

    You can get a smaller cab with BB4 (2.43 cubic feet, Fb=51, F3=49), but you lose some bass extension.

    I would also build a modest high pass filter into the Delta 12LF box, so you can use it to power the other cab, but keep the lows confined to the Delta. Otherwise, you will most likely get bass cancellation between the cabs that produce the bass range.
  12. snowdan


    Feb 27, 2006

    the other cab is my combo. no way to feed the signal back into it.

    i don't understand why there should occur bass cancellation. ???
  13. snowdan


    Feb 27, 2006
    how about 50 liters, sealed, delta 12LF? looks sensible in Win ISD.

    what's missing: a tweeter? i need one, for sure. suggestions?
  14. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    When two sources reproduce the same information their outputs can meet in an out of phase condition, and they can cancel each others output.
  15. The Delta 12LF has an EBP of 100. It is designed for a vented cab.

    Yes, you can always put it in a sealed cab.
    Yes, it will drop at least 3dB in loudness level.
    Yes, it will have less bass extension.
  16. snowdan


    Feb 27, 2006

    i know.

    but why should the speakers be out of phase? the speaker of the cab and the one in my combo will be in one plane.
  17. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Their phase relationships are based on how far apart they are, not the plane that they're located on. Their outputs will only non-destructively couple when the distances between their radiating planes is less than a quarter wave length. This is more problematic in the midrange than in the bass when the cabs are in close proximity, a low pass filter on the Delta LF would keep it's midrange output from interfering with that of the combo, while a high pass filter on the combo would prevent it wasting power on low frequencies that it cannot reproduce.
  18. Would this be an issue in a stack with a 4x10 and a 2x10, or 4x10 and 2x12?
  19. Here's how it works in vented boxes:

    1) At the tuning frequency (Fb), virtually all the output comes from the vent, not the speaker cone.

    This remains essentially additive up to about 90-degrees, after which point it subtracts from the bass output. The additive range is narrow and straddles the tuning frequency. As the frequency moves below Fb there is a point where the output from the vent is 180-degrees out of phase with the cone motion. The cone goes in, the vent goes out...

    2) At the tuning frequency, the vent is 90 degrees out of phase with the cone. There is a time period required to excite the cabinet to resonance, which is why the vent output is delayed behind the cone motion. Since all the output comes from the vent, it is a non-issue, and non-cancelling.

    Knowing the above, if we have two different cabs tuned at different frequencies, their vent outputs are out of phase with each other, and with the cone in the other cabinet. This can result in a suckout from phase cancellation.

    The pro sound guys learned this pitfall a long time ago. Never mix subs of different types/tunings, and never mix reflex subs with bass horns.

    [ edit ]

    If you want to use multiple cabs, use a crossover to keep the bass range confined to one. Use the 4x10 for the bottom, and the 2x10 for the top. Or, use two 4x10 or a pair of 2x10, etc. Just don't mix 'n match different bass cabs that are producing the bass range.
  20. snowdan


    Feb 27, 2006
    so how can a 8x10 work while my combo+extension is a worry?

    i mean if you are right then all our stacks must sound crap.

    my resulting 2 12" drivers would be about 12 inches apart.

    oh yes and both my combo and the extension are (respectivley will) be sealed.

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