MCM 55-2421 8” driver VS everything

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Tom Smit
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Re: MCM 55-2421 8” driver VS everything

#61 Post by Tom Smit »

Seth wrote: Tue Feb 22, 2022 8:26 pm I've also become a fan of handles. Specifically, handles cut into and fashioned from the native material. Of all the mass produced, manufactured screw on type handles I've had my hands on, none have matched the robustness and comfortable feel in the hand of the one's I've made by following Bill's plans.
Ah, shoot! Where did that "like" button go? :lol: I usually come here after I do a quick scan on FB, and I might hit the like button there a few times.LOL.
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ACUA
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Re: MCM 55-2421 8” driver VS everything

#62 Post by ACUA »

Making progress, slowly but surely. At this point I will be really sad if these MCM drivers prove too low quality or the 8” dia size compromises the design. I have been pouring blood and money into this. I wish I had a better shop and some pro grade tooling to use. Between the $55.00 per sheet bowed and flawed plywood and all my hand tool limitations, these builds are hard.

Wild hair, I put some bracing into the sealed portion of the driver chamber for fun, not sure I needed to just found my self wanting to!!! :fruit:
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Seth
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Re: MCM 55-2421 8” driver VS everything

#63 Post by Seth »

Is it me, or is that a day or two away from making noise? Looking darn good :thumbsup:
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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AntonZ
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Re: MCM 55-2421 8” driver VS everything

#64 Post by AntonZ »

Looking good indeed ACUA :cowboy:
ACUA wrote: Thu Mar 10, 2022 11:45 amWild hair, I put some bracing into the sealed portion of the driver chamber for fun, not sure I needed to just found my self wanting to!!! :fruit:
There is no such thing as too much bracing. From that point of view, I'd say well done. I don't think your cab will fall apart anytime soon and that is an understatement.

Just for any future endeavours: bracing in general is meant to prevent the panels from flexing when pressure increases/decreases on one side of the panel relative to the other side. The flexing tends to max out right in the middle of your panels. Your braces are mostly in the corners, where there is less flexing going on. This style of bracing is not useless: it strengthens the connection between the panels. However it would have been even more effective right in the middle of each panel.



Nitpicking session is over. Normal service will now resume :fruit:

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Bill Fitzmaurice
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Re: MCM 55-2421 8” driver VS everything

#65 Post by Bill Fitzmaurice »

Those braces won't have any effect, as they're so close to the corner joints, the strongest place in the cab. A compression strut brace would be useful if it was at least 6 inches out from the corner, and if there was no bracing on the opposite side of the panels being braced.

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Re: MCM 55-2421 8” driver VS everything

#66 Post by ACUA »

I see your point.
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Re: MCM 55-2421 8” driver VS everything

#67 Post by ACUA »

Final side installed, all handles cut in. I wanted the handles as wide as possible, I did not account for the plastic cabinet corners. I may have placed the handles so wide that the corner protectors overlap. Darn, was not thinking about it. At this point I am saving my money for the drivers and some duratex!
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ACUA
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Re: MCM 55-2421 8” driver VS everything

#68 Post by ACUA »

I saved my monies up and purchased some MCM 8” drivers. I am putting a lot of faith in these super cheap little drivers. I bought 8 of them. At $30 ea I only spent what one Lab12 driver costs, crazy! I also ordered the parts to complete the cab, corners, connectors, gasket tape and a gallon of duratex, roller grade.

When I used to be all into car audio I would use Herculiner bed liner. I really liked the durability and ability to cover blemishes. It was $10 more so I optioned for the official duratex.

I finally put the door flanges on today, tomorrow I will make the door. My progress is little by little, bit by bit. I find that a $12 pair of rustler jeans from Walmart is worth the cost as I can just wipe the PL on my pants and then when they get really nasty just toss them!
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Tom Smit
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Re: MCM 55-2421 8” driver VS everything

#69 Post by Tom Smit »

ACUA wrote: Sun Apr 03, 2022 7:42 pm little by little, bit by bit.
That sounds so familiar, but, I can't place it.
ACUA wrote: Sun Apr 03, 2022 7:42 pmI find that a $12 pair of rustler jeans from Walmart is worth the cost as I can just wipe the PL on my pants and then when they get really nasty just toss them!
:lol:
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Rich4349
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Re: MCM 55-2421 8” driver VS everything

#70 Post by Rich4349 »

2 DR250s, 2 27" Lab15 T-60s, 2 30" Neo Titan 39s, 1 Autotuba...and looking for more!

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

#71 Post by Seth »

My intuition has proven itself to be about as reliable as "the truth" from a teenager... but it keeps telling me this is going to work out quite well and I really really hope it's right this time!

I'm very anxious to hear of the final results :thumbsup:
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

#72 Post by ACUA »

Built the door today, got an email saying my drivers shipped
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Re: MCM 55-2421 8” driver VS everything

#73 Post by ACUA »

They came, they finally came!

I wanted to show you the tool I use to install my drivers into the enclosures, little ratchet thingy. I’m going to build the horn up with no finishing effort and demo it out and see how it goes. More to follow.
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ACUA
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Re: MCM 55-2421 8” driver VS everything

#74 Post by ACUA »

Partsexpress specifies a 506.7cm^2 Sd for the Eminence Lab12. Calculating the Sd myself of the MCM 55-2421 I get 213.8cm^2 and two drivers is 427.6cm^2. This means the two 8” drivers has 84% the Sd of the 12” driver. Calculating the exit area for a 24” wide tuba45 576sqin and my cab is 18.5in wide for 444sqin is 77% the surface area.
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Re: MCM 55-2421 8” driver VS everything

#75 Post by ACUA »

So today I did some initial testing of my 18.5” tuba45 dual MCM55-2421 8” subwoofer. I set up one of my 24”wide tuba45 loaded with lab12. Both cabs were placed facing my back wall outside about 12” off the wall as seen in the picture. I was about 8 ft back from the cabs with my meter. The meter I used to do these initial tests is an old RadioShack spl meter. I started with the 24” wide cab, set the voltage output to 2.83v and ran some tones through the rig. I ran sweeps today between 35-48hz only. At one watt about one meter wall loaded but outside the 24” cab put 91dbspl on my meter with a peak at 48hz of 96dbspl.

Now help me out on this one, if the driver is 6ohm and the cab adds 2ohm for a 8ohm nominal, (2.83v/8)x(2.83)=1watt. So with my dual MCM8”s in series I have 8ohm plus 2 from cab for nominal of10ohms, right? Then (3.165/10)x(3.165)=1watt. so in order to try and match power to spl I ran my 18.5in wide cab at 3.165v.

At 35hz on 3.165v same setup as before yielded 91dbspl at the meter. Then peaked on 48hz at 97dbspl same 3.165v. This excited me sweeping across this 35-48hz range had similar response between the two cabs just going off my hand held spl meter.

For today I ended my little session on some peaks. My limiter is set to stop at 47-48v, I tapped out my 24” lab12 cab on 35hz at a peak 114dbspl at 47.5v and then hit it again at 60hz same 47.5v for a peak 122dbspl on my meter. Then I did the same thing with my 18.5” MCM sub, on 35hz at 47.5v I measured 112dbspl and at 60hz same 47.5v 118dbspl. I realize that my meter is not the most accurate unit but I am pretty confident with it plus or minus a db.

I would like to set up my room eq wizard tool and measure the sweeps and over lay them graphically. That will take me a few days to sort out.

So far this cab I built does exactly what I hoped it would. I ran the cab a far bit at 45v sweeping around 35-50hz. I have not blown a driver as of yet. The next test will be to see how long those drivers hold up to abuse over time.

Thanks to everyone for the support, more to follow!!!
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