the MB212 "kit-built" project (intro.).......

[fdeck]

Amp tone is mainly determined by:

1. Overall volume
2. Frequency response curve, on and off axis
3. Distortion
4. Possibly other minor effects

Overall volume is whatever your amp can produce. I think Step 1 is to measure the response curve of the amp and speaker, to know what you are dealing with, at least in broad terms.

 

[DTM]

There is a real shortage of nice 4 ohm or 16 ohm woofers. The 3012HOs only come in 8 ohms, and are so much better in small boxes than anything else that I wouldn't consider many other drivers an upgrade.

When it comes to eliminating boom in severely undersized enclosures the 3012HO is the boss of 12" woofers. Extremely loud as well.

Needing more volume than 500 watts into two 3012HOs is extremely unlikely, especially if your normal one is enough.

Guess I won't be needing an extension cab capability if I have to ultimately use the 3012HOs (I was looking forward to doing that little job)!

Re the 3012HOs versus the current MB212 speakers..........
Could there be THAT much difference between these two speakers?

I presume that the (MB212) speakers are custom-built for GK - you will not find them on the Eminence website. Interestingly you won't find them on the GK website (Store/Speakers) either!
Thus I cannot find any specs or T-S parameters on these speakers (for those of you who could compare them).

Perhaps Mr. G would be kind enough to provide them for us?

 

[DTM]

Also true, provided the baffle is thick enough. I consider 3/4 inch adequate with lightweight drivers.

The MB212 has a 1/2"baffle.
I understand that 3/4" would provide more "meat" for the screws to grip on.
As rpsands does, I could always add small squares of wood to take care of that problem (currently the screws protrude into the cabinet - maybe 1/4").
However, would you consider 1/2" to be "inadequate" for the baffle itself?
If so, what would the best fix be?

 

[billfitzmaurice]

However, would you consider 1/2" to be "inadequate" for the baffle itself?

1/2" is fine for the baffle, just as it's fine for the rest of the cab, if the cab is properly constructed and braced. In my designs if the baffle is 1/2" I specify Tnuts and bolts, if it's 3/4" or more I specify screws.

 

[ClassicJazz]

Sounds like a fun project, good luck with it! Just curious, what kind of bass are you using with it? Reason I ask is I've found the MB212 to be the total opposite of what you described. Mine has a very tight clean punchy tone. You are able to hear all my notes very clearly and still move some low end air. Granted, almost any amp will sound great when you plug a Sadowsky into it! Out of all the bass rigs I've, I have gotten the most complements from this one, and from other bass players. I know for me, muddy and boomy would not describe the tone I get.

 

[rpsands]

It's highly improbable that the 3012HOs would be a *massive* upgrade, but it's distinctly possible they'll be a significant upgrade.

There is a loudspeaker measurement suite you can get from parts express for around 100 dollars, I believe, that will give you many if not all of the TS parameters of the speaker. Bill could possibly hook you up with a link to that if you're really curious.

I would only consider replacing the woofers if the batting and bracing does not fix the issue. You want to do this incrementally so you know what actually makes the difference.

 

[Stompin Tom]

An observation I made on my attempts to rebuild my MB115 is that there was nothing but raw butted joints on all the inside seams on the cabinet. I sealed all the seams with PL construction adhesive and added insulation. I also mounted the speaker properly with t-nuts and hex bolts.

I've been considering this cab (cause I like 15s and the size and weight seem amazing), and I'm pretty handy with this sort of stuff. HOw's it sound now with your mods?

 

[greenboy]

There is a loudspeaker measurement suite you can get from parts express for around 100 dollars, I believe, that will give you many if not all of the TS parameters of the speaker.

It was developed by these Invalid Link Removed guys, but in spite of its higher number the Parts Express / Dayton unit is not considered as nice as Invalid Link Removed by guys who've used both, guys who also have used high-end stuff... Though I think Dayton has recently had a minor upgrade that may address some areas.

Anyway, I've had Invalid Link Removed on my fEARful links page for about a gazillion years. They are the real deal, and a lot of loudpseaker gurus are doing serious development using their products, guys that also have the expensive stuff.

 

[DTM]

Go buy some 3/4" poplar round dowels from Lowes. Brace so that no area of panel greater than 6" is unbraced (e.g. space your dowels out 6" apart) as nearly as you can achieve.

No Lowes or Home Depot where I am, but I can access dowels.
1\2" is the largest diameter I can find so far.

Regarding palcement;
are you suggesting bracing in all 3 axis (i.e. side to side, front to back, AND top to bottom)?

The cabinet has only one factory brace - 2" x 3/4" placed (horizontally) between the center of the front baffle and the center of the rear wall.
I had already made 2 similar pieces to "T bone" this existing brace in the middle, going from side to side (not yet installed).

 

[DTM]

[Invalid or Expired Link Removed]

Great stuff on your site!

Re damping material - have noted the 1 1/2" "egg crate"foam.

Had previously seen another also on the PE site, "Sonic barrier" in 3/4" and 1 1/2" sizes (a lot more expensive than the foam).
Wondered if this would be any better than just the "egg crate" foam - or is this just a lot of hype and extra cash for another acoustic "wonder product"?
If it really IS any better then I don't mind paying the extra cash!

Because I'm overseas and not in the US it takes a lot longer for me to get the "special" bits I need to complete this project.
So I am trying to compile a list of everything I need for a "one time" shipment.

 

[billfitzmaurice]

Wondered if this would be any better than just the "egg crate" foam -

No. It's better if what you're lining is a sheet metal enclosure, i.e., a car door.

 

[DTM]

No. It's better if what you're lining is a sheet metal enclosure, i.e., a car door.

Noted, with thanks.

The money saved on acoustic foam will be the start of my new "Jack 12 Fund"!

 

[michaeln]

I think the speakers in all of the new MB combos are "Paragon" speakers, which are Chinese and made for GK.

 

[DTM]

Not sure if this attachment will work - first time I have done it!

Attached is (should be) a preliminary drawing of how I plan to attack the bracing problem.

Greenboy, I have taken the liberty of looking at your 1212sub and used a somewhat similar layout for the MB212.
Please have a look at it and make any suggestions you feel are appropriate.

The area behind the port is of particular interest - I'm not sure if I am "allowed" to intrude into the airspace between the port and the back plate.
If "NO", then I have already made some errors.
If "Yes", then I need to know if the intrusion I have IS acceptable? (this would be the lower, left corner of the "pillar girdle", viewed from the front).

Perhaps I have gone a little "overboard" in my efforts to (over) brace the cab.
Whatever the case, your feedback is very much appreciated.

Just hope you can make sense of the drawings!!

Thanks.

 

[DTM]

Forgot to add this drawing of the baffle - added a couple of braces there as well.

 

[rpsands]

I think you'd be better off with dowels in that box. Just my two pence. Easier, takes up less interior space, etc. Bill made a good diagram of how to do it.

 

[billfitzmaurice]

Just hope you can make sense of the drawings!!

Thanks.

I can't, 2D doesn't cut it. This is what you want to do:

 

[rpsands]

If you need a source for the dowels, Lowes makes a very nice poplar dowel that's pretty reasonably priced.

 

[BurningSkies]

If you need a source for the dowels, Lowes makes a very nice poplar dowel that's pretty reasonably priced.

Probably not too many Lowes in the "Middle East".

 

[rpsands]

I just figured he was referring to the area north of Alabama but south of New Jersey