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Discussion Starter #1 (Edited)
I currently have an old SVS PC12 and am looking to upgrade. I have two small areas behind my recliners, right next to my loveseat (MLP) that I would like to build two subs for.

The spaces are just big enough to fit the flatpack that PE sells for the UM18, a 4 cuft sealed box, 23x20x21. I plan to power them with an NX6000D.

I had initially thought that two 18" subs known for their low end with "3000 watts" a piece would certainly best my 10 year old in the under 30hz range (my main reason for upgrading), but I went to data-bass to make sure. From what I know, my sub's response closely mirrors that of the PB12 NSD, which does 93 db at 16hz, 103db at 20hz, and 105 at 25hz+.

If that's true, then i guess what I was hoping for was a maybe 107db flat down to 16hz? I honestly have no idea, I'm kind of a noob when it comes to all these subwoofer numbers. Then I see the UM18 "only" does 100db at 16hz, and that's out of a 6 cuft box! I know two subs will supposedly give an extra 3db, but I'll also lose some with the smaller box.

I'd love to go ported, with a tune in the 14-16 hz range, but I know it's pretty much impossible to tune a small box low, because the giant ports subtract from the available box space, right?

So I'm wondering if for my case, external ports might be the answer? Since they'll be right next to the loveseat, that has a good bit of room behind it, couldn't I extend some "bolt on" ports back there? Is there any way to model external ports in WinIDs or whatever that program is y'all use?

I'm not sure how much space is taken up by ports in say, an 8 cuft box tuned low, but I would think it'd be substantial? By having my ports outside the box, could I essentially make my 4 cuft box a 6 cuft box, if you follow my logic? Would porting this even have much of a positive effect?

Finally, if all of this is a bad idea, is there a driver that would better fit what I'm trying to achieve?
 

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I'd love to go ported, with a tune in the 14-16 hz range, but I know it's pretty much impossible to tune a small box low, because the giant ports subtract from the available box space, right?
It's not even necessarily the space taken up by the port as much as the cross-sectional port area that a certain size box can support at a given tune that becomes the major limiting factor.

So I'm wondering if for my case, external ports might be the answer? Since they'll be right next to the loveseat, that has a good bit of room behind it, couldn't I extend some "bolt on" ports back there? Is there any way to model external ports in WinIDs or whatever that program is y'all use?
WinISD models based on net volume, so it's very easy to model external ports, just ignore their volume in the volume you enter.

I'm not sure how much space is taken up by ports in say, an 8 cuft box tuned low, but I would think it'd be substantial? By having my ports outside the box, could I essentially make my 4 cuft box a 6 cuft box, if you follow my logic? Would porting this even have much of a positive effect?
By adding external ports, you are essentially making the gross volume bigger but not changing the net volume. So it's just a 4cf net box, as it was before.


At 4cf net, you could port it at, say, 20Hz with a big enough port (6") that port compression isn't a major issue, but IMO you're still not going to gain enough over sealed at that size to make it worth it. It only gets worse from there (more port limited) if we tune lower. I'm a huge fan of ported subs when their advantages can be leveraged, but this is just not one of those cases. I would absolutely go sealed at this size.
 

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External ports are modeled the same as internal ports. WinISD uses net box volume for calculation, which means it is up to you to subtract the volume of the port, bracing, driver, etc. to give it the box volume shown in the program.


Modeling an external port just means the box volume you input into WinISD is the interior volume minus bracing and driver only. It will tell you the port length needed for the tuning frequency you choose. you can change the port diameter and it will update the length accordingly to keep the tuning frequency static.


This is the conundrum of WinISD. You choose a box size, calculate the internal volume, input it and the tuning frequency into WinISD, which gives you port length required (based on diameter or port dimensions chosen). Then you have to look at the port volume and realize that the box volume you put in originally is actually too large, but reducing the box volume based on the port volume also changes your port... At some point you just have to realize that the iteration of these things does not make a ton of difference to the box tune, so as long as your box volume takes into account the approximate port volume, you'll end up pretty close for resulting tuning frequency. It gets worse as you get into very large diameter, long ports, which take up a lot of internal volume.


Ultimately, having an external port is easier to model.


Edit: I do agree with Aron's final comment though, that at 4cuft you aren't really leveraging the benefits of ported anyway. He beat me to posting, lol.
 

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I'd love to go ported, with a tune in the 14-16 hz range, but I know it's pretty much impossible to tune a small box low, because the giant ports subtract from the available box space, right?
Mainly, because it's impossible to get the length of port you need (with the diameter great enough to not suffer port compression) inside the small box. Your idea of an external port is great, but I would never put a UM18 in a ported 4cuft box. Probably wouldn't do much better than leaving it sealed.
 

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Discussion Starter #5
Thank you so much for your replies!

I'm assuming WinISD only runs on Windows? I'm limited to mobile for a while till i can rebuild my computer. If anyone is bored and wants to model any of this I'd be interested in the hard numbers.

It only gets worse from there (more port limited) if we tune lower.
Could you elaborate a bit on this? What would be required to tune at 15hz? What mechanics would likely prevent this?
 

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Discussion Starter #6
Mainly, because it's impossible to get the length of port you need (with the diameter great enough to not suffer port compression) inside the small box. Your idea of an external port is great, but I would never put a UM18 in a ported 4cuft box. Probably wouldn't do much better than leaving it sealed.
Is there possibly a better driver for the job?


How come consumer subs, say from Rythmic, PSA, or HSU, seem to be able to make ported subs with low tunings in smaller profiles than the DIY community? Why are DIY subs always so big, and under 18hz tunings seem impossible unless it's some 12 cuft monstrosity? Is there something I'm missing?
 

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If anyone is bored and wants to model any of this I'd be interested in the hard numbers.
I did as I was posting. I modeled 4cf net tuned to 20Hz with a 6" port @ 43" long, with a 15Hz HPF BW2. Port velocity was at 19-21 m/s from ~13-21Hz, and it was still +/- 1dB compared to sealed in that entire range.

Could you elaborate a bit on this? What would be required to tune at 15hz? What mechanics would likely prevent this?
If you want to tune at 15Hz, you either have to make the port much longer (you can't or you'll run into port resonance issues) or you have to make the port smaller. Now that 6" port shrinks down to 4.5" @ 44" long. The port was already getting pushed to its limits with the 6" port at 20Hz tune, it will only be worse with a smaller port and lower tune.
 

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Is there possibly a better driver for the job?
You could put a smaller, weaker, cheaper driver in a 4cf box tuned to 20Hz and make it work with reasonable port velocities as it won't push the port as hard. With that comes less output, so is it actually better at that point? You're limited on space and willing to buy a pair of UM18s and an NX6000D. You aren't really going to do any better than that as far as output in that much space for that much money.

How come consumer subs, say from Rythmic, PSA, or HSU, seem to be able to make ported subs with low tunings in smaller profiles than the DIY community? Why are DIY subs always so big, and under 18hz tunings seem impossible unless it's some 12 cuft monstrosity? Is there something I'm missing?
There's no magic going on with their designs. Go find a particular ~4cf sub from one of those companies and post it here and I'll show you that your UM18 4cf sealed option will beat it. ;)
 

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Is there possibly a better driver for the job?


How come consumer subs, say from Rythmic, PSA, or HSU, seem to be able to make ported subs with low tunings in smaller profiles than the DIY community? Why are DIY subs always so big, and under 18hz tunings seem impossible unless it's some 12 cuft monstrosity? Is there something I'm missing?

Heavy DSP with amps that will allow it. Rythmik is servo controlled which is a different beast altogether. PSA builds great subs, but looking at their designs, are also using DSP to compensate. And their lower tuned options aren't exactly small, like 8cuft internal. Hsu is well-regarded, but given the size and port area, are going to suffer port compression and chuffing issues at the levels we DIY fiends demand.

FWIW, DSP is a valid approach, but I think you'd be surprised at the output capabilities of the DIY subs designed around here compared to consumer subwoofers. Especially when additional DSP is involved.

The problem is really that the UM18, and all the UMs for that matter, need larger ported boxes per their T/S parameters.


Edit: I also have to say - I have nothing against those consumer subs - all three mentioned build very nice, capable subwoofers. They work within parameters forced by shipping dims and the general pop's usual restraints on size. If size were no issue, you can bet they'd be selling 12cuft monstrosities as well!
 

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Heavy DSP with amps that will allow it. Rythmik is servo controlled which is a different beast altogether. PSA builds great subs, but looking at their designs, are also using DSP to compensate. And their lower tuned options aren't exactly small, like 8cuft internal. Hsu is well-regarded, but given the size and port area, are going to suffer port compression and chuffing issues at the levels we DIY fiends demand.


FWIW, DSP is a valid approach, but I think you'd be surprised at the output capabilities of the DIY subs designed around here compared to consumer subwoofers. Especially when additional DSP is involved.
DSP doesn't change peak output, it can't make a port-limited sub any less port-limited. The consumer sub designs are limited in output compared to a 4cf sealed UM18 and have ports that are too small IMO. DSP is pretty much irrelevant in this comparison, it just shapes the FR but can't change headroom.


The problem is really that the UM18, and all the UMs for that matter, need larger ported boxes per their T/S parameters.
I disagree. The problem is that the limitation on a ported box is, in almost every case, the port. I see people post this all the time about the UM18, but using a smaller ported box just makes for a smaller port which is even more limited. The UM18 will max out the port in pretty much any design.
 

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Is there possibly a better driver for the job?


How come consumer subs, say from Rythmic, PSA, or HSU, seem to be able to make ported subs with low tunings in smaller profiles than the DIY community? Why are DIY subs always so big, and under 18hz tunings seem impossible unless it's some 12 cuft monstrosity? Is there something I'm missing?
You're comparing your ported 12 to a sealed 18 in a box that's basically too small. Kind of an unfair comparison. A large woofer is usually going to always need a larger enclosure.

If you haven't already bought the 18s, and are limited to that exact flat-pack box size, then you should maybe buy smaller subs and save a few bucks(15s maybe?). Find what works best in that size enclosure.

As @aron7awol has already mentioned, there's no magic going on. And a lot of manufacturer specs are false advertising. Some of them also use dynamic eq to make a pretty graph, but isn't indicative of the response at high volume levels.
 

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DSP doesn't change peak output, it can't make a port-limited sub any less port-limited. The consumer sub designs are limited in output compared to a 4cf sealed UM18 and have ports that are too small IMO. DSP is pretty much irrelevant in this comparison, it just shapes the FR but can't change headroom.
For the most part, I agree with this, however, DSP can bring up the low end to make the +/- 3dB values stated on spec sheets. Yes, I agree, that when pushed to the extremes, port compression limits this low end and input of more power results in diminishing returns or no returns at all. Port limited is still port limited. I was simply trying to explain that the frequency responses stated on spec sheets are not rated at the upper end of SPL output. In fact, most testing performed on consumer subs will definitely show this. Very well-regarded consumer subwoofers will show a reduced output in the lower octaves as the voltage input is increased. They will not remain flat to 16Hz or whatever they are rated at.


I disagree. The problem is that the limitation on a ported box is, in almost every case, the port. I see people post this all the time about the UM18, but using a smaller ported box just makes for a smaller port which is even more limited. The UM18 will max out the port in pretty much any design.

True, high excursion drivers definitely max out ports sooner. Shoot, my Avalanche 15s in 20cuft were maxing out vent velocities for a 6" port, so I was forced to move to an 8" diameter port to keep port speed within reasonable limits.



I still believe that large Vas drivers require larger boxes to maintain reasonably flat native frequency response in ported enclosures. Reducing the box volume just increases the natural roll-off and negates any increase benefit of the port output. Is that not correct?
 

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Is there possibly a better driver for the job?

How come consumer subs, say from Rythmic, PSA, or HSU, seem to be able to make ported subs with low tunings in smaller profiles than the DIY community? Why are DIY subs always so big, and under 18hz tunings seem impossible unless it's some 12 cuft monstrosity? Is there something I'm missing?
FYI: VBSS has an18" driver 15hz tune and is about half the volume you mentioned at about 6cuft. They work very well too I might add. I was happily surprised!
 

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For the most part, I agree with this, however, DSP can bring up the low end to make the +/- 3dB values stated on spec sheets. Yes, I agree, that when pushed to the extremes, port compression limits this low end and input of more power results in diminishing returns or no returns at all. Port limited is still port limited. I was simply trying to explain that the frequency responses stated on spec sheets are not rated at the upper end of SPL output. In fact, most testing performed on consumer subs will definitely show this. Very well-regarded consumer subwoofers will show a reduced output in the lower octaves as the voltage input is increased. They will not remain flat to 16Hz or whatever they are rated at.
I don't disagree with any of that, I just didn't think it was relevant to the OP's question:
How come consumer subs, say from Rythmic, PSA, or HSU, seem to be able to make ported subs with low tunings in smaller profiles than the DIY community? Why are DIY subs always so big, and under 18hz tunings seem impossible unless it's some 12 cuft monstrosity? Is there something I'm missing?
He wasn't asking how they achieve flat FR, he was asking how they make ported subs with low tunings in smaller profiles. How do they do that? Well, it's easy, they compromise on port size and output, nothing related to FR or DSP.

I still believe that large Vas drivers require larger boxes to maintain reasonably flat native frequency response in ported enclosures. Reducing the box volume just increases the natural roll-off and negates any increase benefit of the port output. Is that not correct?
Again, you're suddenly talking about flat native FR, which is not what we were talking about, but I'll go along. Put the sub in a room and you're going to EQ its response anyway by a lot more than whatever small difference there is in native response shape, so what really matters, if anything, is which sub has more headroom. The sub is port-limited down low whether you put a UM18 in it or an SQL-15 in it. So even if one driver looks technically a bit flatter in a smallish ported box on the Max SPL graph or its native response, what happens when we account for the port limitations?
 

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FYI: VBSS has an18" driver 15hz tune and is about half the volume you mentioned at about 6cuft. They work very well too I might add. I was happily surprised!
I'm a big fan of the VBSS, but a UM18 sealed 4cf beats it easily.
 

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I don't disagree with any of that, I just didn't think it was relevant to the OP's question:

Meh, I'm not trying to argue. I was not denying the small box, small port, compromised output. I'm still fairly certain they EQ the low end up on most of those, or they lower output at the upper range to produce the flat response shape, plus smoothing DSP. I never denied the max headroom issue with port compression/velocity either, and I wasn't attempting to be combative. In this manner, they can semi-overcome some of the shortcomings of smaller ported boxes. A much larger portion of the population is actually NOT bass maniacs like us, and may not ever play them loud enough for this to be a problem.

I never said it was to my liking either. If it was, I definitely wouldn't have built a 20cuft ported monster, with plans for a second 18cuft box here soon.


Also, I do believe the OP does not realize that 93dB at 16Hz versus 100dB at 16Hz is a fairly huge difference in output for a single box situation.
 

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Is there possibly a better driver for the job?

How come consumer subs, say from Rythmic, PSA, or HSU, seem to be able to make ported subs with low tunings in smaller profiles than the DIY community? Why are DIY subs always so big, and under 18hz tunings seem impossible unless it's some 12 cuft monstrosity? Is there something I'm missing?
You could put a smaller, weaker, cheaper driver in a 4cf box tuned to 20Hz and make it work with reasonable port velocities as it won't push the port as hard. With that comes less output, so is it actually better at that point? You're limited on space and willing to buy a pair of UM18s and an NX6000D. You aren't really going to do any better than that as far as output in that much space for that much money.

There's no magic going on with their designs. Go find a particular ~4cf sub from one of those companies and post it here and I'll show you that your UM18 4cf sealed option will beat it. ;)
FYI: VBSS has an18" driver 15hz tune and is about half the volume you mentioned at about 6cuft. They work very well too I might add. I was happily surprised!
I'm a big fan of the VBSS, but a UM18 sealed 4cf beats it easily.
I just threw that in there because the OP was asking about "better driver for the job". The job is undefined. 14-16hz...for HT? 2 channel music? Does he have something to fill in the MB? The UM18 is def an earthquake. From what I've read, the VBSS is more efficient at anything above 50hz and it still drops to 15hz if you make it (DSP, raw power). I'm sure the UM18 in a sealed box would beat the VBSS in the 15hz zone...if you make it. The OP does not have a UM18 or a VBSS and likely either one with a few kW would take his living room to a whole new level. :)

Personally, I have yet to hear (feel) a UM18 and would love to. Someday...

BTW: Going from 93db to 100db @ 16hz is a very significant jump and add to that a few thousand watts and see what happens.
 

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Discussion Starter #18
I did as I was posting. I modeled 4cf net tuned to 20Hz with a 6" port @ 43" long, with a 15Hz HPF BW2. Port velocity was at 19-21 m/s from ~13-21Hz, and it was still +/- 1dB compared to sealed in that entire range.


If you want to tune at 15Hz, you either have to make the port much longer (you can't or you'll run into port resonance issues) or you have to make the port smaller. Now that 6" port shrinks down to 4.5" @ 44" long. The port was already getting pushed to its limits with the 6" port at 20Hz tune, it will only be worse with a smaller port and lower tune.
Thank you, that is all very interesting, port tuning is still quite the mystery to me!

You're comparing your ported 12 to a sealed 18 in a box that's basically too small. Kind of an unfair comparison. A large woofer is usually going to always need a larger enclosure.

If you haven't already bought the 18s, and are limited to that exact flat-pack box size, then you should maybe buy smaller subs and save a few bucks(15s maybe?). Find what works best in that size enclosure.

As @aron7awol has already mentioned, there's no magic going on. And a lot of manufacturer specs are false advertising. Some of them also use dynamic eq to make a pretty graph, but isn't indicative of the response at high volume levels.
Actually, I'm mostly comparing them to subs like the the Rythmik FVX15, PSA V1512DF, and HSU VTF3-MK5. They were the "affordable" subs that were pretty close to fitting in these spaces, and all tuned in the teens, with the Rythmik being tuned at 12hz! I realize these are all 15's and I'm wanting an 18", but i figured the larger driver would only help.

For example, data-bass has the Rythmik at [email protected], from a box that measures 24x24x18! I see now that it's considered a 6.5cuft box; I thought it was much closer to the 4cuft of my 23x20x21 box. These measurements seem very close, is there some difference in the way they're being measured? Maybe my flatpack is subtracting for the bracing and subwoofer volume while the Rythmik box isn't?

I'm a big fan of the VBSS, but a UM18 sealed 4cf beats it easily.
That's interesting! I had considered the VBSS, but it seemed to be a bit too tall for what i was wanting. I'd love to see the output numbers; it's a shame the VBSS and the Marty variants aren't on data-bass, it'd be nice to see them represented as well when trying to chose a sub.

Also, I do believe the OP does not realize that 93dB at 16Hz versus 100dB at 16Hz is a fairly huge difference in output for a single box situation.
That's actually a great point. The best sub I've ever heard in my life is sitting right behind me, so I really have no idea what I "need". I know i don't need to much more in the 30-80hz region than what i currently have, but i would like to get the under 30 hz range a large boost, and also keep the subs nearfield, to maximize my enjoyment while minimizing neighbors annoyance.
 

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Discussion Starter #19
I just threw that in there because the OP was asking about "better driver for the job". The job is undefined. 14-16hz...for HT? 2 channel music? Does he have something to fill in the MB? The UM18 is def an earthquake. From what I've read, the VBSS is more efficient at anything above 50hz and it still drops to 15hz if you make it (DSP, raw power). I'm sure the UM18 in a sealed box would beat the VBSS in the 15hz zone...if you make it. The OP does not have a UM18 or a VBSS and likely either one with a few kW would take his living room to a whole new level. :)

Personally, I have yet to hear (feel) a UM18 and would love to. Someday...

BTW: Going from 93db to 100db @ 16hz is a very significant jump and add to that a few thousand watts and see what happens.
Sorry, i know I'm a bit all over the place. The "job" is a slight upgrade from 30-80hz over what i have currently (3db? who knows!) and in a perfect world, a flat response down the 13hz or so. The subs will be nearfield, in small (11.5x14') open concept living room, with vaulted ceilings that go from 8' to 11'. I currently have a full Chane 5.1 (a5.5, a2.4, a1.5) powered by an old Yamaha RX-V3800 7.1, 140wpc. The SVS PC12 is my current sub.
 

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If you have the coin to spend on drone cone(s), passive radiator boxes (with DSP) can blur the extra out put of ported boxes vs. sealed in a smaller form. No concerns about port velocity, noise, or resonances. Steeper rolloff, increased losses (vs. an optimized port, whatever that means) and extra cost are the downsides.

Chris
 
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