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Adding Port Tubes to a GK MB150s/112 Microbass combo. Thoughts?

Discussion in 'Amps and Cabs [BG]' started by miamigroove, Mar 28, 2016.

  1. miamigroove


    Apr 21, 2005
    Have a great little combo amp, the GK MB150S/112. Long since out of warranty, Ive been thinking about modding it by adding some bass port tubes to it.
    First, I changed the 12" speaker out from the stock model to a cast iron frame EV Black Shadow 200W.

    Next, was thinking about adding 1 or 2 bass port tubes to the bottom, rear corners. Probably would only be able to have them between 1-3" length to fit inside. Not sure about port diameter, length, etc.

    Before I cut holes in the aluminum & destroy the stock enclosure, was wondering if anyone could share their thoughts as to why I should / should not do this.

    BTW, I used to have an older MB200 combo from the 80's with a similar aluminum enclosure and I added a bass port to the back. As I recall it did improve the bass response significantly...

    One last note, I nearly always use this combo in conjunction with a Markbass NYC Randy Jackson 15" cab. Together they sound great as-is at home but ive tried to do some medium size club dates & I still cant "feel" the bass onstage. So thats the main reason im considering doing this mod, to get a bit more "air" & low end out of it.
  2. You need to find out the replacement speaker's requirements for cab volume (interior WxHXD) for a ported enclosure is met by the existing "box". If it is too small no porting will make up for the miss-match and the speaker may be damaged by over excursion even at low power levels with ports stuck in there. Diameter and length of ports is determined after the enclosure meets the specific speaker's needs (T/S parameters).
    alaskaleftybass likes this.
  3. alaskaleftybass

    alaskaleftybass Will Hanbury, Jr. Supporting Member

    Mar 21, 2012
    Sitka, Alaska
    Yeah, like B-string said! :laugh:

    The cab was designed optimally as a small enclosure and only so much volume would ever come out of the cab, due to the internal volume. I've seen the back port modifications in the past, and while that might be cab suicide I'd do that before drilling holes in the front.

    If finances permitted, you might consider getting a newer more powerful head to run on top of your Randy Jackson Markbass cab. I'll bet 300-500 modern Class D Watts would really double or triple the output of that cab compared to the older 150 watts you're pumping into it. And that would save your GK combo for smaller gigs and leave it intact as it was meant to be.

    Good luck!
  4. basscooker

    basscooker Commercial User

    Apr 11, 2010
    cincy ky
    Owner, Chopshopamps.com
    Why did you "swap out" the speaker? Was the speaker you put in it suggested? If not, why did you choose it? Bass cabs aren't as friendly with "rolling" as guitar cabs. You can make a great box crap, or make an amazing speaker suck.... Just by popping in speakers willy nilly without the proper research. You can luck out on rare occasions, but typically not. I suggest a decent higher powered head for the 115 and put the orig speaker back in the combo.. Then leave it alone. You didn't mention if your speaker change made an improvement. But you did mention that when used together with the other cab it isn't very full. Are they in phase with each other?
  5. The best reason I can think of for you to do this is that you are better at designing cabs than GK.
  6. do not port this thing
  7. BogeyBass


    Sep 14, 2010
    ts parameters don't have a thing to do with port length. all you need to know is internal volume and port size.

    likewise the benefit would be extended bass response and power handling just like any other reflex/ported cab.

    as long as the enclosure is 1.5 to 2.5 cubic feet I don't know why everyone is so worked up. the bigger concern is the replacement driver might require a ported cab and could /would perform better. likewise cabinets are not very driver specific lol. certain volumes and port tunings work fine with hundreds of drivers. and manufacturers even recommend volumes that vary. going to big volume wise and tuning to high would only mistake. not problem here.
    measure volume and tune to 50Hz...done
    Last edited: Mar 28, 2016
  8. basscooker

    basscooker Commercial User

    Apr 11, 2010
    cincy ky
    Owner, Chopshopamps.com
    The question isn't as much about whether or not it will work, but if it will be an improvement worth the cost and effort to you.

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