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Thanks for the input and suggestion, I’ll definitely look at the SDR18 from Skar.

At this point, I’m leaning heavily toward two sealed UM18-22 in 4ft3 enclosures, both powered by an NX3000D.

I know it’s slightly underpowered, but my hope is that it will be adequate, and that I can achieve -10dB from ref levels from maybe 15hZ and up.
You definitely can't go wrong with the UM18! That's a fantastic driver, you'll be very satisfied with that!
 

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Thanks for the input and suggestion, I’ll definitely look at the SDR18 from Skar.

At this point, I’m leaning heavily toward two sealed UM18-22 in 4ft3 enclosures, both powered by an NX3000D.

I know it’s slightly underpowered, but my hope is that it will be adequate, and that I can achieve -10dB from ref levels from maybe 15hZ and up.
From looking at measurements I guesstimate that dual sealed UM 18" on a 3000D would have ~3-4 dB more output at and around 20 hz tune of your current 12" ported sub. So 6-7 dB more with 6000D (which I say bite the bullet and get correct amp/driver combo from get go.) Of course much, much more output from dual 18's above and below the tune of your current sub.

In original OP you stayed
"Should have mentioned...currently I have a single 12” Monolith, that I’m very happy with, just want a bit more output, especially near 20Hz and slightly under. These will REPLACE the monolith."

So if current sub can play -13 dB from reference levels "near 20 Hz and slightly under", then dual sealed 18" UM's on 3000D will play "near 20 Hz and slightly under" at -10 to -9 dB. Then accordingly with the 6000D as powerplant would play at -7 to -6 dB from reference levels easily at and around the tune of current sub.
 

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Discussion Starter #24
Thanks Luke!

When modeling, what kind of wattage did you simulate from the 3000D? 500w per sub or so?

I would have expected more than a 3dB gain going from the single Monolith 12 to dual UM18’s, but then again, I am looking at underpowered sealed enclosures.

I may not even notice a 3dB gain “at or around tune” if my Monolith.
 

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Discussion Starter #25
I have already ordered the UM18s and the 3000D, so I need to do some thinking on what enclosure now. My plan was the qty 2 sealed 4ft3, due to size/decoration constraints in our family room, but for only 3dB, perhaps I need to get more creative.

I may be able to do something between a Johnny and Mini Marty, if I keep the base about 21” x 21”, I should be able to build it 45” tall or so, then, construct some built-in shelves around and above to help blend in/get approval.

Looking at some rough numbers, an 18Hz tune may not be doable at 21” W x 21” D x ~44” T, seems my port will be a) too low cross sectional area, which I assume will drive up velocity; or b) too long, which I assume will have some other ill effect. Looks like 20Hz tune might be easier to achieve.

I’ll keep digging and update as I work my way through this build.
 

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The ill effect of a long port is how much space it consumes, build complexity, and materials. If you're size constrained then an enormous port is going to be add to your woes, so you make a compromise on port velocity which you do by reducing the cross sectional area of the port, and the calculated length for that given tune shrinks.

Are you using round ports or slotted? With slotted you can get a lot of port area pretty quickly by folding back and forth. I just built a slotted Voxel with a whopping 25" long port for a measly little 0.370 cuft box. It works fine, even with a 180° turn.
 

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I've got 2 of the 4.3cft UM18-22's sealed in a bigger room and they rock. If it were me, and you're even a little bit of a DIY-guy (and I guess you are because you're here), I'd build the sealed first. You've already got the expensive stuff. The enclosures are cheap and easy to build. You don't even have to paint it. Build it. Set it up right. See how you like it. If it's not enough, then go figure out how much of a Marty you can squeeze in. If you like them, take them back to the garage and finish them and be happy :)
 

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Discussion Starter #28
I've got 2 of the 4.3cft UM18-22's sealed in a bigger room and they rock. If it were me, and you're even a little bit of a DIY-guy (and I guess you are because you're here), I'd build the sealed first. You've already got the expensive stuff. The enclosures are cheap and easy to build. You don't even have to paint it. Build it. Set it up right. See how you like it. If it's not enough, then go figure out how much of a Marty you can squeeze in. If you like them, take them back to the garage and finish them and be happy :)
I like your approach here. I think this is what I will do. While I can do a larger enclosure, it’s going to snowball into a wall of painted built-in shelves etc to help blend in. Sounds like a good future project.

I think I’m going to do down firing (if UM18 is okay with that) to keep my kids from beating on the woofer like a drum 😂.

Question for you, what are you powering your pair of UM18s with?
 

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I've seen people on this forum do down-firing UM18's so it should be just fine. The only thing is that you won't get to see their awesomeness. I definitely understand having to protect them though.

I'm using a 6000D but wouldn't worry about using the 3000D. The worst that'll happen is that you'll leave some headroom on the table. I'd be willing to bet that you'll like what you hear.
 

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Discussion Starter #30
I've seen people on this forum do down-firing UM18's so it should be just fine. The only thing is that you won't get to see their awesomeness. I definitely understand having to protect them though.

I'm using a 6000D but wouldn't worry about using the 3000D. The worst that'll happen is that you'll leave some headroom on the table. I'd be willing to bet that you'll like what you hear.
Oh, I want to see them, but am just too afraid my two boys will find a way to destroy them!

Thanks again for your input, and everyone’s input, much appreciated.
 

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I think I’m going to do down firing (if UM18 is okay with that) to keep my kids from beating on the woofer like a drum 😂.
I've never used a UM downfiring, but as mentioned, others have. I've never had an issue with ones I have used in that orientation. Here is the generalized formula for calculating sag. It looks fine, but doesn't take into account the long term effects.

Resources - Woofer Mount Up Down
 

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Thanks Luke!

When modeling, what kind of wattage did you simulate from the 3000D? 500w per sub or so?

I would have expected more than a 3dB gain going from the single Monolith 12 to dual UM18’s, but then again, I am looking at underpowered sealed enclosures.

I may not even notice a 3dB gain “at or around tune” if my Monolith.
No need to simulate UM 18, it has been thoroughly measured at data-bass.com in sealed enclosure. I was looking at the comparison with the HSU VTF 15H V1 (I bet within a dB or two ~20 Hz of your current sub) as well as the lms 12 driver (better driver than your monoprice) in the vmp enclosures. Also looking at audioholics reviews of your sub but different testers so measurements not easily compared.

UM 18 cea burst at 20 hz was 92.5 volts and it measured 7.44 ohm there so 1150 watts distortion limited to 104.9 dB. You will be about half that power so down ~3 dB so ~101.9 dB cea burst, with two so ~107.9 dB. Vtf 15 did 104.1 dB. So yeah ~ 3-4 dB difference.




The UM 18 needs a lot of space for ported enclosures. Its surface area is like having four of your 12's so it needs enclosure 4 times larger than your current sub to be properly ported. Look those two drivers sealed on that amp will have more output everywhere with room smoothing of duals and will be a noticeable upgrade. If you are regularly clipping the amp, get a 6000 down the road. Still not enough, easy double up and add another 6 dB.

My bother in law had lot of space behind screen and runs dual UM 18 in full marty's flat to 17 Hz on the 6000. I run quad 18 sealed flat to 10 Hz. Those UM drivers have a real tough cone, not sure if downfiring is necessary unless your kids are going to take a knife or screwdriver to the surround.:)

Good luck
 

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Discussion Starter #33
Well, I went ahead and built some front firing enclosures. Will hopefully get the drivers installed tomorrow.

9EC90CE5-1C3A-42E3-919C-706B55978423.jpeg
 

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Very Nice!!!
 

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Discussion Starter #37
Well, pretty good, overall I am happy. The output is certainly stronger than the old Monolith 12.

Ended up picking up two used Crown XLS 1500 amps, one bridged per sub, the NX-3000 fans were a rather annoying, didn’t want to mod at this time.

Saw a pretty big improvement with the new/used Crown amps, definitely more headroom.

I need to get a mic, and possibly MiniDSP HD.
 
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