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

[R Baer]

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

The 3012's are going to almost certainly have a different "tone" than the MB212 stock drivers. Whether or not that's a good thing, or not, is all up to your personal tone preferences. I've seen enough post on TB with players raving about the MB212's that I don't think the cab's drivers are really the issue here.

 

[billfitzmaurice]

I've seen enough post on TB with players raving about the MB212's that I don't think the cab's drivers are really the issue here.

I'd agree with that. The drivers probably are fine, but shortcuts do seem to have been taken with the enclosure.

 

[DTM]

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

Sorry it was only 2D Bill.
But thanks for the beautiful 3D "painting"!

Seriously though, I understand the concept of what both you and rpsands are saying re the 3/4"dowels.

Problem here is that the MB212 layout is NOTHING like, or as easy as, the example you gave.
It is far more constained on the baffle and has far less space inside to be able to go from one side to the other, especially if you are looking for symetrical, or ideally 6" spacing as rpsands suggests.

I will attach another (2D -sorry again Bill) drawing - this time uncluttered and showing the approximate internal dimensions of the MB212.

Bill, I don't know if you have the time (or inclination) to transcribe this drawing into 3D?
If you do it will become obvious as to the constraints or restrictions this cab presents for "cross-dowel" bracing.

That is the reason I tried out greenboys bracing first - it is more symetrical and will cover the panels better than the dowels will IMHO!
Yes, it will be more work, and I'm not sure if it won't create other problems which at this stage I am not even aware of?

 

[billfitzmaurice]

That is the reason I tried out greenboys bracing first - it is more symetrical and will cover the panels better than the dowels will IMHO!
Yes, it will be more work, and I'm not sure if it won't create other problems which at this stage I am not even aware of?

Braces applied to the panels is better than nothing, but pales in comparison to panel to panel bracing. A single brace connecting two opposing panels in the middle is as effective in reducing vibration as doubling the panel thickness.
You only get one chance to do something the right way. By all appearances G-K missed that boat. I wouldn't repeat the error, especially when all it takes your part to get a superior result is an investment in time.

 

[DTM]

Braces applied to the panels is better than nothing, but pales in comparison to panel to panel bracing. A single brace connecting two opposing panels in the middle is as effective in reducing vibration as doubling the panel thickness.
You only get one chance to do something the right way. By all appearances G-K missed that boat. I wouldn't repeat the error, especially when all it takes your part to get a superior result is an investment in time.

Thanks Bill.
Couldn't agree with you more regarding doing things the right way!
I just don't see very many options for the placement of panel-to-panel dowels in the MB212.
Perhaps you would be kind enough to give me your idea as to the best way to position them in this cab?
Thanks.

 

[billfitzmaurice]

Thanks Bill.
Couldn't agree with you more regarding doing things the right way!
I just don't see very many options for the placement of panel-to-panel dowels in the MB212.
Perhaps you would be kind enough to give me your idea as to the best way to position them in this cab?
Thanks.

Top to bottom, side to side, front to back. There's no need to brace within six to eight inches of any corner joint, so with the size of that cab perhaps three braces connecting the sides and two the top and bottom and front and back will be adequate.

 

[DTM]

Top to bottom, side to side, front to back. There's no need to brace within six to eight inches of any corner joint, so with the size of that cab perhaps three braces connecting the sides and two the top and bottom and front and back will be adequate.

Thank You Bill.

I'll make another drawing with the dowels placed as close to your suggestion as possible, and then submit it for your approval!

Take a while.........................

 

[DTM]

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

Bill, Here's my attempt at 3D, just for you

The positioning of the dowels is not exact but reasonably close.
Your comments please?
(I gave up trying to draw speakers, hence the open holes)!

The 2 cross dowels below the speakers have about an 1/8" clearance (I imagine that is sufficient)?

I have assumed that where the dowels cross one another they should NOT touch, and have left about a 1/16" between them.

One of these dowels goes across the back of the port. Is this a problem (a "no no")?

I have not included any front-to-back bracing (other than the factory brace) - there are only a couple of places to do this and I'm not sure it would make much difference because of that?

Hopefully the drawings will reproduce acceptably!

 

[billfitzmaurice]

Bill, Here's my attempt at 3D, just for you

It looks OK, just keep the dowels as close as possible to the mid line of the panels. A couple more connecting the baffle to the back would be in order; as those are the largest panels they're the most prone to vibration.

 

[Emprov]

It looks OK, just keep the dowels as close as possible to the mid line of the panels. A couple more connecting the baffle to the back would be in order; as those are the largest panels they're the most prone to vibration.

How much will the bracing effect the internal volume and, by extension, tone of the cab?

 

[billfitzmaurice]

How much will the bracing effect the internal volume

Imperceptibly.

and, by extension, tone of the cab?

Energy expended vibrating the cab walls is energy that doesn't end up as useful output. Panel vibration also can create phase cancellation issues between the sound created by the panel flex and that of the speaker output. There are no downsides to well braced cabs, and no upsides to poorly or unbraced cabs.

 

[DTM]

How much will the bracing effect the internal volume.......

Empty volume of the cab (subtracting the port and amp box) is approimately 3.0cu ft.
Total volume of the bracing (including 2 possible front-back braces not shown in the drawing) is 0.20 cu ft.
Net volume is thus 2.80 cu ft.

 

[DTM]

A couple more connecting the baffle to the back would be in order; as those are the largest panels they're the most prone to vibration.

Thanks for your advice Bill.

I will attach a couple more (3D) drawings.

Because of the lack of suitable space for front-to-back bracing, will this work as a compromise?

I have put one dowel front-to-back, and then I have "T-boned" 2 strips of 2" x 3/4" ply between the factory brace and the sides, against the back of the Baffle (as shown).
I thought that this might be a better solution than another front-to-back dowel - there did not seem to be a really good location for a second one?

 

[DTM]

A couple more connecting the baffle to the back would be in order.....

Bill, Here's the only other solution I could come up with - perhaps better than the "T-Bone" idea?

 

[Jerry Ziarko]

With all that said, were you able to turn the XLR jack around?

 

[billfitzmaurice]

Bill, Here's the only other solution I could come up with - perhaps better than the "T-Bone" idea?

It's better than the TBone, which wouldn't do much at all. But they don't do anything to brace the largest free spans of the back. To fix that I would run a couple of braces at an angle from the joint of the factory brace and baffle to the 1/3 points in the back. By the look of it the box that the amp is in may provide adequate bracing for that area of the back, so perhaps just one angle brace to the middle of the other end of the back would do.

 

[DTM]

With all that said, were you able to turn the XLR jack around?

Nope!
The XLR is "hard-pinned" into the PC board and I didn't want to mess with that.
If it had been loose wires I could have reversed the plug with a little effort.

Not a big deal - I can live with the XLR - just a little peeved at the lack of QC and design planning!

Mr.G likes the sound of his MB212 - guess he also likes the way his XLR is installed?

 

[DTM]

.......... .so perhaps just one angle brace to the middle of the other end of the back would do.

Thanks Bill - your advice is invaluable!

I'll get working on that right away.

 

[DTM]

............so perhaps just one angle brace to the middle of the other end of the back would do.

Bill, the single rear angled brace is cut and dry-fitted (took longer to do the drawing than the actual brace)!

Attached is one more drawing showing the angled brace (in its approximate position).

If you are satisfied that the bracing is complete, I will get into the "production" phaze and start glueing it all together!

Thanks.

 

[billfitzmaurice]

If you are satisfied that the bracing is complete, I will get into the "production" phaze and start glueing it all together!

Thanks.

After installed and the glue has cured rap your knuckles on the cab. The sound should be a high pitched solid whack. If it's a low pitched hollow thud, like a drum, you need more bracing.