Help with DIY extension cab

Discussion in 'Amps and Cabs [BG]' started by JACink, Jan 13, 2015.

  1. JACink


    Mar 9, 2011
    I have contemplated various times about building DIY extension cab for my GK MB112 combo. Mine is the older model, so it doesn't have the output for the MBP extension cab.

    As my combo was in need of a good clean, today I took it apart (for the first time in probably 3 years) and whilst doing so, checked out the insides.

    I'm not sure how many of you are familiar with the interior of this combo, but it is a very simple cab, with no dampening material, or extra bracing etc.


    After checking online the model number of the driver, I have found various places that sell them for less than 80€, so I even thought about a 212 cab, but 2x 112 would make more sense. It is a Paragon 12", although I cannot find any more specs than 200W @ 4Ohms (a couple of places say 300W, but I believe 200W makes more sense).


    I took internal measurements of the cab, and the only "strange" shape inside the cab is where the amp is located at the back.


    So my question is, if I take the overall internal volume (and port dimensions) and make an identical internal volume, just in a basic cube shape, should this sound the same as the current cab?

    Is there anything important point that I am overlooking?
  2. INTP


    Nov 28, 2003
    Dallas, TX
    Adding a second 4 ohm driver will result in 2 ohms (assuming you run parallel) and the amp probably isn't going to be stable at 2 ohms. You could run them in series and get 8 ohms, but you'll get less power from the amplifier and will roughly offset the benefit of the second driver.

    I don't see it being worth it to add a passive cabinet for this combo amp.
  3. JACink


    Mar 9, 2011
    Sorry, I didn't clarify that I would be running this cab (or 2) from another amp.
  4. vdub75


    Feb 15, 2013
    Yes, you are overlooking that your amp has a minimum load of 4 ohms so with an extension cab you will be flying it. at 2 ohms.

    get a pair of eminence basslite S2012, replace the speaker in your combo with it and build an extrension cab in similar size.
  5. INTP


    Nov 28, 2003
    Dallas, TX
    If you match the driver, internal volume, and port, and use a separate amplifier to drive it, I cannot think of a reason why it wouldn't work fine. Cube shape can cause problems, though. LxWxH shouldn't be even multiples of each other.
    T_Bone_TL likes this.
  6. JACink


    Mar 9, 2011
    Thanks @INTP, when I said cube, I should have actually said sort of rectangular, basically the same shape as the combo but without the space for the amp at the back. So taking the total volume and making it the same but a little shallower.

    However, thinking about it, the space at the back would probably be useful for storing cables etc.
  7. JACink


    Mar 9, 2011
    Bump, just to see if the evening (for me, midday/afternoon for you) crew have anything to object. :)
  8. B-string

    B-string Supporting Member

    G-K makes their own drivers, I did plot one of my 16 ohm 12s with DATS. I don't know what the Xmax or Xlim would be.
    * This data was exported from DATS the Dayton Audio Test System
    * Manufacturer: G-K
    * Model: NEO 12 16 ohm
    * Piston Diameter = 260.4 mm
    * f(s)= 51.14 Hz
    * R(e)= 13.38 Ohms
    * Z(max)= 167.7 Ohms
    * Q(ms)= 7.684
    * Q(es)= 0.6661
    * Q(ts)= 0.6129
    * V(as)= 20.84 liters (0.7359 cubic feet)
    * L(e)= 1.889 mH
    * n(0)= 0.399 %
    * SPL= 88.11 1W/1m
    * M(ms)= 185 grams
    * C(ms)= 0.052 mm/N
    * BL= 34.55
    * K(r)= 0.1548
    * X(r)= 0.4809
    * K(i)= 0.01457
    * X(i)= 0.7141

    Copying the existing cab would at least be predictable.

Share This Page