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Double Bass G-K MB150 Speaker Replacement?

eadg57

eadg57

Gold Supporting Member
Sep 7, 2005
144
15
SF Bay Area
#1
Anyone have any experience replacing the 12" speaker in one of these combos? Specifically, I am looking for guidance regarding the assembly which connects the back of the aluminum cabinet (with a machine screw) to the back plate of the speaker (with a rubber bumper.)

The back plate of my old speaker is flush, but the new driver I received from G-K has a ~1" hole in the center.

Any shared experience appreciated.
 
#2
There are several players here on TB that have done the replacement. I do know that GK switched from using Pyle to I think Eminence sometime in the 90’s. Those cabinets are known to be difficult to reseal, but it can be done. Hopefully, someone who has experience with this will chime in. Francis Deck FDeck here on Talkbass may have done the replacement.
 
#6
dylanjohnson said:
There should be a rubber spacer that is screwed in from the back of the cabinet that keeps the back of the amp from vibrating. This may have changed in different ways in different generations of the amplifier.
Click to expand...
Thanks, Dylan. Yes, that rubber spacer, and how it seats against the back of the magnet, is the area of my concern.

When I placed in the new speaker and gasket (with the unit on its back), I could feel that the speaker was contacting the rubber spacer, but could not see the point of contact.

Do you have any thoughts on how snug that fit needs to be? My rubber spacer was a little deformed from the previous years of use, so I wonder if an adjustment is indicated.
 
#7
I don't believe it is dead center on the magnet of the driver, more on the upper half, so if there is a hole in the middle, it should still be ok. I'd spin the spacer so that the maximum pressure is placed on the back panel. Again, there are multiple models of this amp and the cabs are built differently, so my experience may be different than yours. If the speaker is front mounted then you might even want to put something else in between the spacer and the speaker, as shrinkage may have occurred along with the deformity you speak of. The issues with putting these back together mainly consist of getting an airtight seal with the gasket and making sure that back panel doesn't rattle. Is this a series III?
 
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#8
dylanjohnson said:
I don't believe it is dead center on the magnet of the driver, more on the upper half, so if there is a hole in the middle, it should still be ok. I'd spin the spacer so that the maximum pressure is placed on the back panel. Again, there are multiple models of this amp and the cabs are built differently, so my experience may be different than yours. If the speaker is front mounted then you might even want to put something else in between the spacer and the speaker, as shrinkage may have occurred along with the deformity you speak of. The issues with putting these back together mainly consist of getting an airtight seal with the gasket and making sure that back panel doesn't rattle. Is this a series III?
Click to expand...
Only spin the spacer if the screw from the back that holds it in place is right in the middle, otherwise it might miss the back of the driver.
 
#9
dylanjohnson said:
Only spin the spacer if the screw from the back that holds it in place is right in the middle, otherwise it might miss the back of the driver.
Click to expand...
Thank you for your helpful replies. I now have a much better understanding of what I'm working with.

Yes, this is a Series III, with a 2008 serial number (I believe). I am currently away from the amp, but will add some pictures to help others in the future.
 
#10
I believe the Series III has a welded chassis, which is easier to seal than the earlier versions unless it's damaged. It also uses thicker metal, which will be less prone to vibration. Make sure you have a really great seal when you put on the gaskets and the speaker. What I would do is go ahead and try to put the thing together if you can feel the rubber spacer hitting the back of the speaker. If the back is vibrating, then go in and try to shim it with more rubber somehow.
Also, be VERY careful not to strip out the screws. All it takes is a little too much torque in your wrist and those things strip straight through the aluminum. Never use an electric screwdriver on those.
 
#13
Here are some pics showing the parts we have been discussing: 1) The old (Eminence) speaker w/ black magnet back, 2) New speaker (GK) with silver back and hole, 3) the rubber spacer mounted to the back of the cabinet, 4) a thin rubber washer I stacked on the existing spacer before carefully reassembling.

Based on some quick measurements and the smudge on the back of the old speaker, it appears that the rubber spacer meets the speaker at just about center.
Old Speaker.jpg
New Speaker.jpg
Rubber Spacer.jpg
Rubber Washer.jpg
 
#15
The issues with putting these back together mainly consist of getting an airtight seal with the gasket and making sure the box doesn't rattle or buzz.
I've had my little GK for many years. The absolute hardest part of taking the MB150 apart is getting ALL the gaskets seated correctly so there is an airtight seal with no "cabinet "buzz", which is HORRIBLE!!! Good luck
 
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#16
I think that may be the reason GK has totally abandoned the Microbass Combos with sealed enclosures (infinite baffle). They work great
until you have to venture inside the cabinet replace the speaker. At the time they were designed, those light weight metal boxes were
a revelation, not so much anymore. I would think that it's much easier to build speaker enclosures out of wood. Just my take. Hope
your experience works out.
 
#17
Just to wrap this up...
My discussion with GK confirmed that the addition of a small piece of rubber (Thanks, Dylan!) will work fine to address the misshapen rubber spacer. They also suggested--and have used--a blob of silicone to make sure there is good contact. The are no thermal or mechanical concerns if the spacer covers the hole on the back of the magnet.

I put everything together and played a gig last night. No issues. Done.
 
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#20
Yes. Words to the effect of: "If you can tell where there is a gap, put some silicone on the spacer before putting the speaker back in. Or just put a blob on there."

I asked if he meant I should let the silicone cure before putting in the speaker. He checked with a colleague, and said, no, the wet silicone will assure there is good contact between the pieces.
 

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