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

[DTM]

This series of posts was started in another thread.
However it really deserves more attention and thus, IMHO, needs its own thread.
If possible I will transfer the few relevant posts here for continuity.

[DTM]

Morning All. Newbie David here.

I have joined this forum for a single-minded and very simple reason, "To fix the sound of my new GK MB212"!

One way or another, I intend to "adjust" my combo, by whatever means necessary, to allow it to achieve its full potential and become the best sounding combo that is possible to do considering what I am starting with.

I look at this as a "personal project" and will try to remain as open-minded and constructive in my comments as possible.
I also therfore consider my MB212 as having been provided in "kit form", with 90% of the construction already completed (and very well I will add), with only the remaining 10%, the "upholstery if you will", left for me to complete!

To Mr, Gallien let me say this; "I bought your MB212 without hearing it (yes, buyer beware) based upon reviews, recommendations and your reputation for building, IMHO, possibly some of the best amps out there.
Weight and ease of transportation by a single person was high on my list of priorities, and I commend you for being at the forefront of this new line of light-weight combos.
I'm sure that you spent a lot of time and effort in tuning the sound of this combo to your specifications.
Sadly, and with all due respect, that sound is NOT to my liking, and I thus intend to modify it.
Futhermore, I have knowingly voided the warranty by dis-assembling the combo for my own modifications, and will not be requesting any support in that regard, except perhaps for advice, if you choose to provide it".

One negative comment.........

I removed the amp from the box to see if I could easily remount the XLR direct-out plug so that the "lock pin" faced outwards (toward the back).
In its current position you cannot get your thumb or finger in-between the cabinet and the plug to unlock it - my ONLY niggle with the build quality and quality control of the combo!!

Enough said.
Let the "kit-built project" begin...................................

[DTM]

For those of you out there that LOVE the sound of your 212 or 210 combos, GREAT!
However, I DON'T like the sound of my 212 - to me it is "confused, muddy, muddled and boomy" (I HATE boomy bass) - and I am here for the sole purpose of trying to improve that sound.

My ultimate goal is turn my 212 into the best sounding combo that it possibly can be, within the limitations of what I have to start with - a 3cu.ft (internal volume), 1/2", ported bass 212 speaker cabinet.

I am not constrained by time for this project - music is a hobby and not my livelyhood - and thus I am prepared to work slowly and methodcally to achieve this objective.
No disrespect to those of you who have resolved your sound issues with some form of acoustic lining and additional bracing.
I am not after a "quick fix".

I would like to start from "scratch" here - by that I mean "build the cabinet from ground up", if you will.

I have titled this a "kit-built" project for the simple reason that the cabinet lies bare - the speakers and amp have been removed - and it is awaiting whatever modifications, major or minor, are needed in this endeavour!

[DTM]

IMHO, it seems to me that in the endeavor to create a light weight combo/cabinet, we may be getting into a "tail wag the dog" situation here.

From the research I have done, and continue to do, the "standard recommended" thickness of material (ply or mdf) appears to be 3/4", for building a cabinet of this size.
Nowhere have I seen 1/2" thickness as being "recommended'!
That does NOT mean that it cannot be done or HAS not been done.

What this appears to imply to me is that, because of the lack of mass and density of the 1/2" material ( as compared with 3/4"), and the addtional bracing etc required to stiffen the cabinet, you MAY start approaching the weight of a cabinet built out of 3/4", thus defeating the "light weight" objective?

I am therefore wondering if this may not be the main reason that some of us have "issues" with the sound of these light weight combos?

For those of you who are the experts in cabinet building and acoustics, please let me ask you the following 2 questions:

1) Would YOU build a 3cu.ft bass speaker cabinet out of 1/2" ply?

2) If "Yes", then exactly how would you do it (bracing etc)?

I thank you in advance for whatever light you can shed on this subject.
As this thread continues I'm sure that many will benefit from your advice, and thus be able to modify their combos to whatever degree they choose.

Below are some approximate dimensions regarding this cabinet:

Int. Dimentions: 25 1/4"H X 17 7/8"W x 12 1/4"D
Int. Volume: 3 cu.ft (accounts for "amp box" intrusion)
Port Size: (rectangular) 9 3/8"H x 4 3/4"W ( x 4 1/2"D)

[thudfromafar]

I dont understand what else you could do besides acoustic lining and additional bracing? Maybe someone else will have another suggestion, but I'm pretty sure that is what everyone else will suggest. I mean, what do you have in mind? Dont know why you're against the damping/bracing as its goal is to fix exactly what you've described...

[greenboy]

Originally Posted by DTM

What this appears to imply to me is that, because of the lack of mass and density of the 1/2" material ( as compared with 3/4"), and the addtional bracing etc required to stiffen the cabinet, you MAY start approaching the weight of a cabinet built out of 3/4", thus defeating the "light weight" objective?

Not even close. The math is easy on which approach weighs less. You should check out the fEARful website and threads before you get too carried away with venturing guesses. And look at Bill Fitzmaurice designs, and barefaced bass and Duke LeJeune, which are some commercial leaders who use 1/2" or even 3/8" for high-performance enclosures.

3/4" is still used by most MI manufacturers because it's cheap quick construction, but oddly enough a lot (most) of those 3/4" cabs could use some bracing too. On the other hand, a lot of commercial subwoofers with considerably higher-force drivers in them use thinner ply and bracing - rather than 3/4" which if to be done right would still require bracing.

[rpsands]

You (the OP - Greenboy is dead on!) are definitely wrong as far as the bracing is concerned. A 1/2" cabinet requires a bit more bracing, but the weight difference is minimal because of the bracing.

I always build out of 1/2" or lighter ply and have never had any issues.

All of the MB cabs have insufficient bracing and damping in my experience from checking them out.

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.

Use PL premium to secure the dowels. Drilling a 1/8" hole for them to sit in with a forstner bit is good.

Then line the cabinet walls with 1" of polyester batting.

That should do it. If it doesn't, replace your woofers with Eminence 3012HOs -- the cabinet is just right for these woofers and they will almost surely be less boomy than the original.

[BurningSkies]

Originally Posted by DTM

IMHO, it seems to me that in the endeavor to create a light weight combo/cabinet, we may be getting into a "tail wag the dog" situation here.

From the research I have done, and continue to do, the "standard recommended" thickness of material (ply or mdf) appears to be 3/4", for building a cabinet of this size.
Nowhere have I seen 1/2" thickness as being "recommended'!
That does NOT mean that it cannot be done or HAS not been done.

What this appears to imply to me is that, because of the lack of mass and density of the 1/2" material ( as compared with 3/4"), and the addtional bracing etc required to stiffen the cabinet, you MAY start approaching the weight of a cabinet built out of 3/4", thus defeating the "light weight" objective?

I am therefore wondering if this may not be the main reason that some of us have "issues" with the sound of these light weight combos?

For those of you who are the experts in cabinet building and acoustics, please let me ask you the following 2 questions:

1) Would YOU build a 3cu.ft bass speaker cabinet out of 1/2" ply?

2) If "Yes", then exactly how would you do it (bracing etc)?

I thank you in advance for whatever light you can shed on this subject.
As this thread continues I'm sure that many will benefit from your advice, and thus be able to modify their combos to whatever degree they choose.

Below are some approximate dimensions regarding this cabinet:

Int. Dimentions: 25 1/4"H X 17 7/8"W x 12 1/4"D
Int. Volume: 3 cu.ft (accounts for "amp box" intrusion)
Port Size: (rectangular) 9 3/8"H x 4 3/4"W ( x 4 1/2"D)

Yes, I would use half inch. And in fact, have two tremendous sounding cabs in half inch. I would brace across the center of the panels, where they need it. Then I would line the cab appropriately with good damping material and that would probably take care of as much as you can without rebuilding from scratch.

Density of material means nothing. Stiffness of material on the other hand is a concern.

[greenboy]

http://greenboy.us/fEARful/variousit...#DampingPorted

http://greenboy.us/fEARful/bracing.htm

[DTM]

WHOA!!!!!!!!!!!!!!
Hardly finished copying and pasting before I was inundated with responses!
I thought that by posting this as a NEW thread it would garner more attention than where it was.
I certainly didn't expect so many responses so fast!
I thank you all very much.

Now that we ALL know the "D" in DTM stands for "Dumb" we can get on with finishing the cabinet.

I'm going to need a little time to digest all of this excellent information before I respond.

However, with reference to a possible change of speakers.......... if I ultimately need to do that then I might as well continue with 16 ohm versions, install a Speakon connector and enable the combo to thus run an extension speaker (like the MB210).

[DTM]

Originally Posted by thudfromafar

I dont understand what else you could do besides acoustic lining and additional bracing? Maybe someone else will have another suggestion, but I'm pretty sure that is what everyone else will suggest. I mean, what do you have in mind? Dont know why you're against the damping/bracing as its goal is to fix exactly what you've described...

Sorry thudfromafar, guess I conveyed the wrong message to you.
I am absolutely NOT against bracing and damping.
In fact exactly the opposite - I KNOW that's what this cab needs.
I am simply trying to find out what the best fix would be in both of those areas - i.e. (1) What IS the best way to brace this particular cab, and (2), when the bracing is completed, what is the best material to use for damping this particular cab?

We all know that there are quite a few people out there who are "unhappy" with the sound of their MB212s (and MB210s), and thus I am hoping that this thread will help all of those who choose to stick WITH their combos rather than sell or return them.

Along with eventually fixing my combo, that IS the sole purpose of this thread.

[rpsands]

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.

[DTM]

Originally Posted by greenboy

http://greenboy.us/fEARful/variousit...#DampingPorted

http://greenboy.us/fEARful/bracing.htm

Thanks greenboy - took a quick look and will be back to study more later. Excellent info. - sorry I did not get there before.

[BigDaddyO]

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.

[billfitzmaurice]

Originally Posted by BigDaddyO

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.

Butt joints are perfectly acceptable so long as the cab is well glued, fastened and braced. But otherwise, not so much.

[rpsands]

I'll note that decent screws are fine for holding up Neo drivers. I like the recex screws from Speakerhardware very well.

[billfitzmaurice]

Originally Posted by rpsands

I'll note that decent screws are fine for holding up Neo drivers.

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

[rpsands]

Originally Posted by billfitzmaurice

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

What I do now is glue little 1" x 1" squares of wood behind each screw hole, and then screw into that. Gets me 1" of screwing surface in each.

In the past I've run dowels front to back behind some of the screw holes, which worked out pretty well.

[StereoPlayer]

subbed, interesting!

[thudfromafar]

Sorry DTM, the misunderstanding must have come from these statements you made.

No disrespect to those of you who have resolved your sound issues with some form of acoustic lining and additional bracing.
I am not after a "quick fix".

I would like to start from "scratch" here - by that I mean "build the cabinet from ground up", if you will.

Anyways, I'm sure you will find a good solution from users here.