MCM 55-2421 8” driver VS everything

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ACUA
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MCM 55-2421 8” driver VS everything

#1 Post by ACUA » Tue Jan 11, 2022 6:16 pm

I am trying to think, :wall: I have had good luck with this little $35.00 driver. I had one in an auto tuba that I thought I had properly abused. I tried to remove it from the enclosure to reuse in my table tuba but I ripped the surround out in the process. I subsequently disassembled the thing to reveal that the coil was still like new. The driver in my new table tuba is impressing me.

Why are these little drivers not applied to the titans or pa tuba series subs? Is the driver just not that reliable? If the eminence lab12 costs $220 a unit and you fit that into a 24” wide cab let’s say it’s in something like a tuba 45 horn. At $35.00 each I could buy 5 units and enclose them in 10” wide horns. For a 50” total width, would that not outperform a single 24” horn loaded with the 12” driver?

Every time I have to move my lab12 loaded 24” wide t45 cabs I can hear the echos of so many on this forum warning me that I would regret it. I do, I wish I had built twice as many that were half as heavy. In my thinking :wall: I had essentially resolved to opt for the budget driver in the future and just build twice as many narrower cabs. Today I am looking at this little 8” driver that could and thinking for the price I could have built 20 t45s between 10-16” wide for what I paid to build my current subwoofer rig. Now I know that would have cost more in wood and materials and been more labor but not by that much. And I could have done it slowly over time. Today I dread moving my tuba 45 subs. Getting weak or old or smart, I guess.

Would I get equally sick of moving all 20 of those smaller but still arguably large subs around am I just being a sissy?
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Re: MCM 55-2421 8” driver VS everything

#2 Post by daveO » Tue Jan 11, 2022 6:30 pm

When you need less speaker, you will also need less amp- double benefit for your back!

Bruce Weldy
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Re: MCM 55-2421 8” driver VS everything

#3 Post by Bruce Weldy » Tue Jan 11, 2022 6:51 pm

ACUA wrote:
Tue Jan 11, 2022 6:16 pm

Why are these little drivers not applied to the titans or pa tuba series subs? Is the driver just not that reliable?
For one thing, they aren't Pro Sound drivers. The specs are within the parameters although Qts is a little low. But, the sensitivity is only 87db with the power rating of 120 watts at 4 ohms. It's take a bunch of those to equal one Lab or 3012LF.

And who knows how they would perform in a horn......can they take the pressure of a sealed box?

Give up a little extension and build T39s. They are easy to move with casters. But, I just can't see spending all the time and money it takes to build these boxes and put a $30 driver in 'em.

6 - T39 4-25" 2-22" 3012LF
4 - OT12 2512 Melded/NSD2005
1 - T24
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

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Seth
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Re: MCM 55-2421 8” driver VS everything

#4 Post by Seth » Tue Jan 11, 2022 8:26 pm

Strictly a function of an obviously relaxing daydream, I've had the same line of curiosity. I bet they'd do quite well in any of the pro sub designs.

I've got to imagine the biggest reason the option isn't talked about much has something to do with the "public image" of the designs. It's hard enough to get the average Joe to believe the "hype" while promoting the use of well known and trusted drivers, let alone trying to sell the validity a $35 off brand eight inch driver loaded cab to a serious gigging professional.

I'd still love to do it, just because. I'd imagine 32 cabs loaded with 8's would likely handle a county fair size gig with ease and headroom to spare. That's still less than $1200 in drivers. 4 cabs series/parallel wired is 4ohms and would take about 50v to drive. Could easily power the whole herd with 4 fairly low cost amps.

And now I'm not gonna be able to stop thinking about it for days! LOL

I do love the thought.
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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Re: MCM 55-2421 8” driver VS everything

#5 Post by ACUA » Wed Jan 12, 2022 9:02 am

Seth, that makes two of us. Silly as it may be, I wish I could sell my four t45s and buy/build an army of narrow cabs. Even if they are not quite as efficient, or the drivers are not as reliable for the cost it still looks logical. If you could build the horns narrow enough no internal bracing would be needed, it would make building much easier.

Surely 4 cabs that are 8” wide, with 8” drivers equalling 28” of horn opening width and 180sqin driver displacement rivals a 24” wide single horn with 120sqin driver displacement of equal excursion capabilities both handling 50v input signal. Lighter cabs to move, it’s a win right!!!

Man I wanna do it!
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Re: MCM 55-2421 8” driver VS everything

#6 Post by Bruce Weldy » Wed Jan 12, 2022 9:31 am

ACUA wrote:
Wed Jan 12, 2022 9:02 am
handling 50v input signal.
While it has a huge xMax, the problem is the thermal handling. With 50 volts at 4 ohms - that's 625 watts. Way more than the max of this driver. You might not blow it up from excursion, but you'll burn it up from heat.

Everything is a trade off. The good xMax is great for lower volume going low. But, it ain't gonna handle much power that you need for PA work. Remember, all of the designs that Bill suggested that driver for are to be used inside - meaning cabin gain. You don't get that very often in a PA.

The other thing to remember is that the volume of the driver box in horns is a very important part of the design. Not sure how well the MCM would play in a box designed for 12 or 15 inch drivers.

But hey, it's a DIY world here - so, give it a shot if that's what you want to do......but, I think just dreaming about it would yield better results. :mrgreen:

6 - T39 4-25" 2-22" 3012LF
4 - OT12 2512 Melded/NSD2005
1 - T24
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

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Re: MCM 55-2421 8” driver VS everything

#7 Post by Seth » Wed Jan 12, 2022 10:52 am

Bruce Weldy wrote:
Wed Jan 12, 2022 9:31 am
ACUA wrote:
Wed Jan 12, 2022 9:02 am
handling 50v input signal.
...With 50 volts at 4 ohms - that's 625 watts....
I'm pretty sure the context is 4 cabs series/parallel wired, yielding +/- 150 per driver.
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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Re: MCM 55-2421 8” driver VS everything

#8 Post by Seth » Wed Jan 12, 2022 11:10 am

ACUA wrote:
Wed Jan 12, 2022 9:02 am
Seth, that makes two of us. Silly as it may be, I wish I could sell my four t45s and buy/build an army of narrow cabs. Even if they are not quite as efficient, or the drivers are not as reliable for the cost it still looks logical. If you could build the horns narrow enough no internal bracing would be needed, it would make building much easier.

Surely 4 cabs that are 8” wide, with 8” drivers equalling 28” of horn opening width and 180sqin driver displacement rivals a 24” wide single horn with 120sqin driver displacement of equal excursion capabilities both handling 50v input signal. Lighter cabs to move, it’s a win right!!!

Man I wanna do it!
Personally, I'd want to build them as wide as possible to take advantage of the horn and let it do as much work as possible. In an effort to lighten the load, I'd be more inclined to see if I could get away with 3/8" ply construction and 1/4" bracing.

I wanna say I recall someone (Harley perhaps?) building a T39 out of 3/8". IIRC, it performed without any sort of deficit. I'll see if I can dig it up.
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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Re: MCM 55-2421 8” driver VS everything

#9 Post by AntonZ » Wed Jan 12, 2022 12:03 pm

Seth wrote:
Tue Jan 11, 2022 8:26 pm
I've got to imagine the biggest reason the option isn't talked about much has something to do with the "public image" of the designs. It's hard enough to get the average Joe to believe the "hype" while promoting the use of well known and trusted drivers, let alone trying to sell the validity a $35 off brand eight inch driver loaded cab to a serious gigging professional.
Bill has designed his PA tops with piezo drivers, which are widely frowned upon yet they perform well. I am pretty sure from that point of view he would not hesitate to use the cheaper drivers for PA subs if they were a viable option. I think they are OK for home use with occasional peaks, but a PA that has them running balls to the wall with hard voltage limiting makes for more thermal and mechanical stress on the drivers. They would not be reliable enough for pro sound use. That is just my uneducated guess though.
Seth wrote:
Wed Jan 12, 2022 11:10 am
I wanna say I recall someone (Harley perhaps?) building a T39 out of 3/8". IIRC, it performed without any sort of deficit. I'll see if I can dig it up.
While not a pro sound sub, I have built my T18 from 3/8" ply (we say 9mm). It was a bit more work to make it fit together due to smaller tolerances. And you need more braces because the thinner ply flexes more under pressure. Standard T18 has single braces straight through the middle. I made mine with double braces. Definitely more time consuming to build. Doing one was fun, I can't imagine doing like 16 of these. If you are aiming for light weight, I'd rather suggest you use poplar ply instead of BB. It dents a bit easier and is not as nice to work with as BB, but it does yield a noticeable weight saving.

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Re: MCM 55-2421 8” driver VS everything

#10 Post by Bill Fitzmaurice » Wed Jan 12, 2022 12:26 pm

AntonZ wrote:
Wed Jan 12, 2022 12:03 pm
I am pretty sure from that point of view he would not hesitate to use the cheaper drivers for PA subs if they were a viable option. I think they are OK for home use with occasional peaks, but a PA that has them running balls to the wall with hard voltage limiting makes for more thermal and mechanical stress on the drivers. They would not be reliable enough for pro sound use. That is just my uneducated guess though.
It's a good guess. In some of the plans for pro subs I mention that it's possible to find consumer grade drivers with T/S specs that are within tolerance but that they should not be used, for this reason.

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Re: MCM 55-2421 8” driver VS everything

#11 Post by Seth » Wed Jan 12, 2022 12:35 pm

Ah! Found it... T39 Lite - worth the gamble? - maybe

A couple excerpts from the thread:
Harley wrote:
Sat Aug 04, 2012 11:35 pm
So, the T39 is 20" wide external. 9mm ( 3/8" ) Italian poplar sides, tops back and panels, 1/2" Australian Hoop Pine woofer baffle and step off, braces from 4mm ply ( the stiffest I could find o the ply store ), 3 braces per width dadoed into panels and staggered.

The ply is a bitch to work worth I must say and controlling warp is a nightmare - BUT - it's real solid construction so far and once the glue sets there's absolutely no movement in the cab.
Bill Fitzmaurice wrote:
Sun Aug 05, 2012 4:16 pm
I wouldn't hesitate to build any of our cabs from 3/8" myself, I just don't recommend it in general as it does complicate the build quite a bit.
Harley wrote:
Thu Sep 11, 2014 1:08 pm
If I was building more T39s for myself, I'd certainly go this way again. They are ridiculously light weight.
Last edited by Seth on Thu Jan 13, 2022 7:57 am, edited 1 time in total.
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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Re: MCM 55-2421 8” driver VS everything

#12 Post by Seth » Wed Jan 12, 2022 1:00 pm

When I built my TAT, I bought extra drivers, fully intending to blow some. I've never had to replace one. I'd honestly enjoy seeing the demise of one, magic smoke OR cone failure.

I do have one more MCM driver on hand and also a 16" T39 I could make a 12" to 8" driver adapter for. Seems like 16" could possibly be an appropriate width for an 8" driver in that cab.

Limited to 25v, I'm fairly certain it won't fail thermally. I put much more than that through them (likely closer to 45v) and beat the piss out of them in the car.

I assume the throat pressures in a T39 are greater than that of the TAT. I wonder if the pressures would be high enough to fail the cone?

I'm also curious to measure sensitivity. The more and more I think about this, the more intrigued I get!
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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Re: MCM 55-2421 8” driver VS everything

#13 Post by Seth » Wed Jan 12, 2022 3:03 pm

ACUA wrote:
Tue Jan 11, 2022 6:16 pm
Every time I have to move my lab12 loaded 24” wide t45 cabs I can hear the echos of so many on this forum warning me that I would regret it.
ACUA, is the typical venue for you indoors or outdoors?
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

ACUA
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Re: MCM 55-2421 8” driver VS everything

#14 Post by ACUA » Wed Jan 12, 2022 8:04 pm

About 50/50 indoor and out. I just received the order for my MCM8” from Newark. So I may just build up a narrow tuba45. Just to play with it. You say 16” wide, any other thoughts on optimum width? I put enough power to my auto tuba to hear audible distortion through the horn often as I would search for the absolute limits of what I could get out of it. I was doing 20-25v long and hard I was shocked when I disassembled the one I mentioned and the coil was not burnt in the least. No coil smell what so ever.

I have half a sheet of plywood left over from my table tuba,one more sheet may be enough for a narrow tuba 45 or should I try a titan48?

Bill recommends the Eminence BP102 10” driver as the least expensive driver in widths of 13-18” and voltages limited to 28v for the tuba45. That driver costs $92.00 on Partsexpress.com. If I build an 18” wide cab and manage to squeeze two MCM55-2421 8” drivers in it it would only run me $80.00 on drivers. Would not this beat a single 10” driver for output quality. I get that we could go wider with dual 8” drivers easily 24-28 inches but for apples to apples being same size cab and less expensive drivers and being better bass for your buck. It really makes me wanna do it.
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Re: MCM 55-2421 8” driver VS everything

#15 Post by Seth » Wed Jan 12, 2022 11:55 pm

I only mentioned 16" wide because it's what I have (T39). Comparing the min/max widths for 10 and 12 inch drivers, it seems 16" would be roughly appropriate for an eight... at least for a test just to see what happens. I wouldn't have to build anything except an adapter ring. However, the cab's at my dads house 350 miles away. So, it's not like I can give it a go in the morning. I'll grab it next time I'm down there.

The Tuba or Titan question... always some great opinions come out of that conversation and all of them seem valid. It seems to me, we have 3-4 things going on in considering the MCM for big boy duty;
Cost, size, weight, and curiosity. Pretty much the same as usual, just different :D

For me it's mostly curiosity. I love small drivers doing big things.

For size and weight, the argument could be made that the 3010LF would be a strong avenue to pursue.

Size and cost is where it seems your interest resides. Which, if you go the route of putting two drivers in a cab, it starts to diminish the size benefit. Although, it does offer in-box series wiring for an 8ohm cab.

I have pretty much come to the conclusion for myself that any indoor only system is Tuba territory and a system that will see any outdoor duty is automatically Titan territory... unless I'm able and willing to potentially double the cab and amplifier count. If I were to build a cab to test the MCM driver, I'm pretty sure I'd choose a Titan in favor of it's overall increased sensitivity. Especially since I'd be interested in maximizing the available output from a small driver. But, that's not to say that I'm not thoroughly curious how well it would perform in every cab design. I completely am. It just feels like the Titan is the right place to start.

On the other hand, since you already have 4 T45's, it might make sense to make a T45 in a size that could take a 12" driver so you could make use of the cab if the test didn't pan out to be a viable option in the end.

Neither is clearly the hands down way to go. Flip a coin?

Do you have casters on your T45's? If not, you may want to add some. They should wheel around effortlessly. Maybe put some 3012LF's in them to help with the weight a little?
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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