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Discussion Starter #1 (Edited)
Hello all, great forum, full of good info. I am new to HT DIY subs, looking to build a new set (qty 2) of HT subwoofers. I have read alot of posts here about the different options. I think I am leaning toward 18” woofers. I have read about the VBSS, Marty(s), Johnny, Cyclops etc.

My biggest constraint is size...I would like to stick with something about 20” W x 22” D x 22” T, something close to this anyhow. I would like to be able to get solid output down to 20Hz, if possible, but I understand that my cab req’s may (will) limit my results.

My room is essentially 20’ x 20’ x 8’, fireplace closes off one corner a bit.

I have been honing in on (Qty 2) UM18-22 sealed (4ft3) units; however am wondering if an NX3000D would have an easier time powering these 2 UM18s (at lower Hz) if I built a Micro Marty for each. I have read that a 6000D is really better for two UM18s, but I think I may be willing to lose 3dB to keep the budgeted 3000D amp.

Would a vented enclosure offer much benefit, easier to drive, at this small cabinet size? I haven’t been able to locate many UM18 Micro builds.

Anyone powered two sealed (4ft3 ea.) UM18s of a single 3000D?

I would expect that the 3000Ds output rating of 900W/channel @ 4ohm is likely closer to 500w/channel @ 4ohm in the real world. But, from my limited knowledge, that’s only 3dB down from giving it the full 1000w RMS.

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.
 

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Discussion Starter #2
Well, I have now realized why I haven’t located UM18 Micro builds, the Micro is for the 390HO 15”... o_O

So I suppose the Cube is my smallest vented option for the UM18.
 

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Discussion Starter #4
No doubt I would prefer full Marty! :)

The height is difficult for the SO to accept, really stands out in the room.

It’s looking like for the NX3000D, perhaps two Marty Cubes w/ the slightly more efficient 460HO may be my best bet; that is, if I can’t convince my SO that full Marty will blend right in :ROFLMAO:.
 

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You gotta let them UM's breathe. I'd do a Johnny sub at the very least. Anything less would be uncivilized.:) The 18HO can work in a smaller box but not by that much, imo.

The SI SQL-15 is good in that size of box if when your S.O. wins. ;)
 

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Discussion Starter #6
Interesting, I’ll take a look at the SQL-15 output, hadn’t really considered a 15”, too excited for a big ol 18 lol.
 

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Discussion Starter #7 (Edited)
Would the SQL-15 work well in a Microcube?

The 390HO Micro build looks very interesting.

That’s pretty darn solid output down to 20Hz (theoretical), plus the enclosure size is exactly what I need. I would suspect I could run qty 2 (unbridged) on each channel of an NX3000D? Looks to be a pretty efficient woofer, so I would suspect that I wouldn’t miss much dB slightly underpowered?

I’m glad you suggested a 15” woofer!
 

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To answer one of the OP's original questions: Yes, you can drive dual UM18s from an NX3k. I have 2 ~5cuft sealed on one channel and a modified VBSS on the other of my NX3k. All depends on the SPL you're trying to hit.
 

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Discussion Starter #10
To answer one of the OP's original questions: Yes, you can drive dual UM18s from an NX3k. I have 2 ~5cuft sealed on one channel and a modified VBSS on the other of my NX3k. All depends on the SPL you're trying to hit.

Thanks for answering that question, I am still considering two 18” UM18-22 4ft3 sealed, run one on each channel of the NX3000D.

Now researching to see if a couple 15” 390HO Micro builds would yield better results, powered by the same amp.

Tough one for me to determine, but that’s what I’m looking into more now.

Either scenario above would be a approximately 21” cube.

I like the idea of the UM18 so I already have the drivers for “future” full Marty’s. 😁
 

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Now researching to see if a couple 15” 390HO Micro builds would yield better results, powered by the same amp.
You would have to define "better results".
What SPL are you after?
What is the goal? ULF, midbass, both?
 

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Discussion Starter #12
For me, better results is going to be typical HT LFE range. I guess I’ve never really thought about this... or never typed it out...maybe ref level from 20Hz to 80Hz?

Anything below that would be nice, but I understand that I need more cabinet volume for that.

With that, another part of better results, is being able to achieve this with an NX3K, due to budget.

I’m not sure if that’s even specific enough.
 

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Missed the 21" cube part, sorry. In that case look into the SI SQL-12 or 15. Haven't seen models/measurements for either but should produce good ULF for that box size. But realize that they probably won't produce much (if any) chest kick in that box.

Again, what are you after?
 

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Discussion Starter #14
I’m new to this addiction, sorry for my lack of clarity, I had a PC-2000, upgraded to a Monolith 12 THX, now I’m looking to upgrade to something with more output.

I want to feel the LFE more, more room pressurization I suppose, and gain more even response across the typical LFE freq range.

I imagine the chest kick you are referring to is likely more mid-bass? Maybe up in the 80Hz and up range?
 

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It’s a little bit more money but a HST-18 will do we I. That size box, maybe a little bigger. I just built four HST-18s in 24 x 24 x 20” boxes and I am getting reference output down to 15hz.


-Trevor
 

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Discussion Starter #16
The HST-18 looks great, but budget wise, couldn’t swing that, would change my amp selection as well. I’ll bet they sound great.
 

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For me, better results is going to be typical HT LFE range. I guess I’ve never really thought about this... or never typed it out...maybe ref level from 20Hz to 80Hz?

Anything below that would be nice, but I understand that I need more cabinet volume for that.

With that, another part of better results, is being able to achieve this with an NX3K, due to budget.

I’m not sure if that’s even specific enough.
LFE range is like 3HZ-120, not 20HZ. 20HZ is where most garbage subs start dying(cough svs). Your leaving a TON of content on the table ignoring under 20HZ. If you're going big with UM18, make sure you dont tune them to high. If going sealed, well enjoy the fun haha. Heres a thought- some will cry but hear me out. My friend and member here @thebudgetaudiophile runs Skar SDR 18's sealed. You can probably get two for the price of one UM18, anyway he just full sends them in his theater and they give him an awesome experience. They may have been a bit shady, but hes running his uncapped(no limiters) balls to the wall and he has zero issues and plenty of ULF to sake your eyeballs loose.
 

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I do run them pretty hard, LOL! I've recommended the SDR 18s to a few people and so far everyone who has followed that advice has been sated. I won't pretend that a $140 drvier will compete with a $500 driver but I will say, hand-on-heart, that they dig deep enough and perform well enough (especially when sealed) that you won't be in want!

I have to give the asterisk(*) caveat that the majority of my experience with the SDR 18 is in my theater, running my house curve, with my EQ, and my particular setup (8 18s and 4 15s) but I can say that the 3 or so people who have said "yeah, for $140/driver, I'll try it" have been very satisfied. I believe the trick with the SDR is running them sealed. Remy has modeled them time and again and no matter where you port-tune them, the model's response is weird (to say the least) so sealed seems to be where it's at for them.

My SDRs are the D2 (dual 2 ohm) version, but they also make a 4-ohm version if your amp is not 2-ohm stable.

I run each VC to it's OWN amp channel across 3 NX4-6000s (so each coil gets a 2-ohm push), EQ everything so 10Hz - 40Hz is pretty equal, then enjoy some movies. I make sure I watch my output lights on the amps (though they rarely go beyond the first LED, even when I'm being naughty), and pay attention to where I set my gains (as you should be doing anyway) and I've had, as Borat would say, "Many Success".

If you decide to go with the SDRs, let me know, if you have any questions about them, comments, or concerns, I'd be happy to walk you through. I'm not a brand-rep or anything, I've just had positive experience with my 18s and the company.
 

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Discussion Starter #19
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.
 

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Remy has modeled them time and again and no matter where you port-tune them, the model's response is weird (to say the least) so sealed seems to be where it's at for them.
With a Qts of .69 that's not surprising. I always considered the UM the minimum viable budget option, but $140 for an 18, if it works for you--great. That's true to your handle. :)
 
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