The right subwoofer for this 2.0 cu/ft box - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 23 Old 04-09-2020, 09:01 AM - Thread Starter
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The right subwoofer for this 2.0 cu/ft box

Hello everyone,

I have two sealed sub boxes that I purchased from DIY SoundGroup several years ago. I assembled them but ended up building 18" subs instead. Now I'm looking to finish them for another secondary room. They are these 2 Cu/ft boxes:

https://www.diysoundgroup.com/flat-p...-flatpack.html

The problem is when I look at the Dayton RS-HF 12" subs, they look like they want a box that is much smaller-- 0.71cu/ft. If I put a port in the cabinet, this sub would work well. But there isn't room on the front baffle for a port, so I'm trying to stay sealed.

And when I look at the 12" Ultimax subs, they want a box that is bigger-- 2.8cu/ft. (Also, that sub is only available in 2 ohms--not sure if I should only be sticking to 4 ohms. I'm building a pair.) The box they package with this sub has two more inches of depth than my DIY Soundgroup box.

Would the Ultimax do okay in a smaller than optimal box? Is 4 ohms vs 2 ohms a factor? (Not exactly sure what it means. I think it has to do with wiring the subs in parallel--but I'm unclear on that.)

Is there another 12" driver you would recommend I look at?

Thanks for any help!
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post #2 of 23 Old 04-09-2020, 09:05 AM
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post #3 of 23 Old 04-09-2020, 09:15 AM
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Quote:
Originally Posted by dftkell View Post
Hello everyone,

I have two sealed sub boxes that I purchased from DIY SoundGroup several years ago. I assembled them but ended up building 18" subs instead. Now I'm looking to finish them for another secondary room. They are these 2 Cu/ft boxes:

https://www.diysoundgroup.com/flat-p...-flatpack.html

The problem is when I look at the Dayton RS-HF 12" subs, they look like they want a box that is much smaller-- 0.71cu/ft. If I put a port in the cabinet, this sub would work well. But there isn't room on the front baffle for a port, so I'm trying to stay sealed.

And when I look at the 12" Ultimax subs, they want a box that is bigger-- 2.8cu/ft. (Also, that sub is only available in 2 ohms--not sure if I should only be sticking to 4 ohms. I'm building a pair.) The box they package with this sub has two more inches of depth than my DIY Soundgroup box.

Would the Ultimax do okay in a smaller than optimal box? Is 4 ohms vs 2 ohms a factor? (Not exactly sure what it means. I think it has to do with wiring the subs in parallel--but I'm unclear on that.)

Is there another 12" driver you would recommend I look at?

Thanks for any help!
Firstly, the UM 12-22 is a 2 ohm dual voice coil sub. This means the sub can be wired in series to present a 4 ohm load and Parallel to present a 1 ohm load. As you pointed out, PE suggests a 2.8 ft.³ enclosure for the UM 12-22, but I believe you would be ok using your 2 cuft cab Actually, I think you'd be ok with either of the drivers you have mentioned.

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post #4 of 23 Old 04-09-2020, 09:58 AM
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You could use the UM10 and build it ported.

edit: I totally missed that the box is already cut for a 12.

Last edited by Samps; 04-09-2020 at 01:31 PM.
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post #5 of 23 Old 04-09-2020, 10:10 AM
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I second the UM12. You'll have a higher Q system, but it won't change the F3 much. Just use lots of fill.

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post #6 of 23 Old 04-09-2020, 12:27 PM - Thread Starter
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Quote:
Originally Posted by Vergiliusm View Post
I second the UM12. You'll have a higher Q system, but it won't change the F3 much. Just use lots of fill.
Okay, thanks. So instead of two lbs of fill, maybe four lbs?
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post #7 of 23 Old 04-09-2020, 01:23 PM
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No, I'd stay around 2.

I had an old Infinity sub a little larger than your box. The driver and amp were sh*t, but the enclosure was solid. I was too busy (sounds better than lazy) to build a box, so I dropped in a UM12, sealed it up, and ran a bridged Behringer 1000DSP. It worked like a champ for its size, until I had some free time ( to build a larger ported box.

I wouldn't have any hesitation at all, and you already got the boxes. They'd be great for a smaller room that doesn't need a lot of output.

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post #8 of 23 Old 04-09-2020, 01:32 PM - Thread Starter
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Quote:
Originally Posted by Vergiliusm View Post
No, I'd stay around 2.

I had an old Infinity sub a little larger than your box. The driver and amp were sh*t, but the enclosure was solid. I was too busy (sounds better than lazy) to build a box, so I dropped in a UM12, sealed it up, and ran a bridged Behringer 1000DSP. It worked like a champ for its size, until I had some free time ( to build a larger ported box.

I wouldn't have any hesitation at all, and you already got the boxes. They'd be great for a smaller room that doesn't need a lot of output.

Sounds great and thanks for the help. It is for a smaller room and I'll have two subs so I doubt they would ever be pushed to anything close to hard.

I've built several subs in the past but always used plate amps. If I were to try to power both subs with a Behringer, can they interface with a Mac to set up the high pass filters, etc? I've avoided using pro amps because it just seemed more complicated.

Thanks!
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post #9 of 23 Old 04-09-2020, 02:32 PM
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I haven't had a Mac for 8 years or so, but I can't imagine a "pro" product that isn't compatible. The big advantage and why they're so popular is watt per dollar. Since it doesn't sound like you're going to push them that hard, you could run them off a NX3000D. One of the nice things about the Ultimaxes is their mechanical stoutness.

I think you'll be pleasantly surprised with the performance for the intended application.
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post #10 of 23 Old 04-10-2020, 05:32 AM
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And watch out for the rabbit hole. You'll be thinking about upgrading to the UM18-22 before you know it

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post #11 of 23 Old 04-10-2020, 09:11 AM
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The only thing a bigger box will do is increase low end efficiency and reduce power handling (because there’s less air spring acting on the suspension).

Depending on the actual size of the cutout, the ScanSpeak Discovery 12 (basically Peerless XLS gen 2) is another to consider.

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post #12 of 23 Old 04-10-2020, 11:06 AM - Thread Starter
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The only thing a bigger box will do is increase low end efficiency and reduce power handling (because there’s less air spring acting on the suspension).

Depending on the actual size of the cutout, the ScanSpeak Discovery 12 (basically Peerless XLS gen 2) is another to consider.
It looks like the ScanSpeak/Peerless 12 does well in basically a 1 cu/ft box. So in this case, my box (2cu/ft) is too big. Whereas in the case of the Ultimax, my box is a bit too small. Do you think it's better for the box to be a bit too big or small?

The cutout = Outer Cutout: 12.4", Inner Cutout 11.2"

Thanks
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post #13 of 23 Old 04-10-2020, 11:16 AM
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Quote:
Originally Posted by dftkell View Post
It looks like the ScanSpeak/Peerless 12 does well in basically a 1 cu/ft box. So in this case, my box (2cu/ft) is too big. Whereas in the case of the Ultimax, my box is a bit too small. Do you think it's better for the box to be a bit too big or small?

The cutout = Outer Cutout: 12.4", Inner Cutout 11.2"

Thanks

Modeling the various driver options in that enclosure will give you much better data than looking at manufacturers box recommendations.

Chris
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post #14 of 23 Old 04-10-2020, 12:36 PM
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The SQL-12 will beat the UM12 by ~4.4dB <20Hz, well worth considering for this 2cf sealed application.

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post #15 of 23 Old 04-10-2020, 12:49 PM
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I can't remember if it was fixed or not but I think PE has the wrong dimensions on the 2cuft subwoofer cabinet page. I think the depth was off a bit but would need to double check that.

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post #16 of 23 Old 04-10-2020, 01:52 PM
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Quote:
Originally Posted by Erich H View Post
I can't remember if it was fixed or not but I think PE has the wrong dimensions on the 2cuft subwoofer cabinet page. I think the depth was off a bit but would need to double check that.

They do on the 4cu as well.

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post #17 of 23 Old 04-10-2020, 06:23 PM
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Originally Posted by dftkell View Post
It looks like the ScanSpeak/Peerless 12 does well in basically a 1 cu/ft box.
They'll do fine in bigger boxes, too. They'll just be more efficient down low.

For example, the late Siegfried Linkwitz's XLS12 based "Thor" sub was about 2 cubic feet.

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Originally Posted by dftkell View Post
So in this case, my box (2cu/ft) is too big.
That's not really a thing.

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Originally Posted by dftkell View Post
Whereas in the case of the Ultimax, my box is a bit too small.
All that means is you'll need to set the EQ differently.

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Originally Posted by dftkell View Post
Do you think it's better for the box to be a bit too big or small?
Box models don't matter if you have electronic manipulation.

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post #18 of 23 Old 04-10-2020, 06:32 PM
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The right subwoofer for this 2.0 cu/ft box

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Originally Posted by DS-21 View Post
Box models don't matter if you have electronic manipulation.
Disagree.

Eq allows you to match the shape of the response, but doesn’t necessarily allow you to match the magnitude.

If your box is small enough, you will either run out of amp or cook your coil trying to push the driver to the same low-frequency output as you can achieve in a larger box

The inverse is not true, you will be able to match the upper end output of a small box with a large box by eq-ing the lower end down to allow the driver to take more power.

My recommendation for box design: Make the box just large enough for the driver to achieve desired excursion on the available amplifier power. Shape the response from there with dsp.
Of course, many people want/need to run a smaller box for a given amp/driver combo. This is fine, just be aware that you’re leaving low frequency output on the table.

Chris
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Last edited by a77cj7; 04-10-2020 at 09:33 PM.
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post #19 of 23 Old 04-10-2020, 07:00 PM
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Originally Posted by dftkell View Post
Would the Ultimax do okay in a smaller than optimal box? Is 4 ohms vs 2 ohms a factor? (Not exactly sure what it means. I think it has to do with wiring the subs in parallel--but I'm unclear on that.)
If you mean this one https://www.parts-express.com/pedocs...ifications.pdf
then it has two 2 ohm coils. Wire in series for 4 ohms. But what amp do you have? And what are its power ratings? Because 2 woofers would make 2 ohms, which is a hard load on any amp, even if the amp is rated for it. Losses/heat in the amp go up much more at low impedances, and it's a long lecture but I believe few amps deliver more actual dynamic power at clipping when loaded down (in part since amps specs are into resistors and speakers are NOT resistors)

Anyway those Ultimax would be fine in 2 cubic feet, the Q would be like 0.8 using a crude online calculator. I'd feel fine using your boxes and just stuffing them well. However, there is nothing wrong with using the other woofer and having a lower Q, it can make a very tight extended response which sometimes meshes better with the room gain. And yes, simulations will show a higher -3 dB point, but Dick Small just chose that for mathematical convenience while writing his thesis. The -6 or even -10 point is more meaningful in a room. I agree you can't port those enclosures effectively, even with rear ports. Not enough depth to tune low.
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You can put a 4" Precision port on the top, bottom, or either side towards the rear of the cabinet. I'm pretty sure you should have depth for the port to be tuned to at least 32hz, and you won't hit xmax until about 26hz.You could even add a little bit of boost at port tuning to extend the bass f3 a little bit lower, that if you have a dsp.
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post #21 of 23 Old 04-14-2020, 07:37 AM - Thread Starter
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Originally Posted by Erich H View Post
I can't remember if it was fixed or not but I think PE has the wrong dimensions on the 2cuft subwoofer cabinet page. I think the depth was off a bit but would need to double check that.
I suspected that might be the case since the picture they show looks exactly like the subs I bought from you several years ago.
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post #22 of 23 Old 04-14-2020, 11:55 AM - Thread Starter
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Originally Posted by head_unit View Post
Anyway those Ultimax would be fine in 2 cubic feet, the Q would be like 0.8 using a crude online calculator. I'd feel fine using your boxes and just stuffing them well. However, there is nothing wrong with using the other woofer and having a lower Q, it can make a very tight extended response which sometimes meshes better with the room gain. And yes, simulations will show a higher -3 dB point, but Dick Small just chose that for mathematical convenience while writing his thesis. The -6 or even -10 point is more meaningful in a room. I agree you can't port those enclosures effectively, even with rear ports. Not enough depth to tune low.
So I'm most likely going to use the 12" Ultimax and stuff it well like you said. But when you say the other woofer would work but have a lower Q, you're referring to the Dayton RS-HF, right? And if you don't mind me asking, what does having a lower Q mean?

Thanks!
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post #23 of 23 Old 04-16-2020, 09:12 PM
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Quote:
Originally Posted by dftkell View Post
So I'm most likely going to use the 12" Ultimax and stuff it well like you said. But when you say the other woofer would work but have a lower Q, you're referring to the Dayton RS-HF, right? And if you don't mind me asking, what does having a lower Q mean?
Yes, the RS-HF has a lower Q by itself, lending itself to lower Q sealed box designs. Q comes from (way back in the day) "Quality factor" and it's a measure of damping I guess you could say. It's kinda how much control the magnet/coil system have over the cone motion, fighting the mass and the springiness of suspension. A lower Q means more control, meaning in particular better ability to stop the cone motion when the audio signal stops. Another way to think of it is as a measure of how sharp or strong the resonance of the speaker is.

Here you can see some tone burst results-the audio voltage on the bottom looks perfect, but the acoustic output (related to the cone motion) does not start nor stop instantly.
https://www.har-bal.com/1052/loudspe...sign-criticism
Too much ringing is heard as a looseness and/or boominess of the sound.

Many sealed box designers shoot for a final Q in the box of 0.707, because this gives the lowest -3 dB point. That's rather misguided, since Dick Small only chose -3 dB for mathematical convenience while writing his thesis. In real rooms, the -6 or even -10 decibel points may be more important. On the other hand, very low Qs start to require a huge box, since the stiffness of the air in the box drives the Q up. The Ultimax Q was I think 0.58, so even a big box pushes the Q higher really fast. The HS' Q is...0.39?? Anyway much lower, so even a smaller box doesn't push the final Q too high.

All this vaguely applies to ported boxes. Those are much more complex than sealed boxes, however we can generally apply a rule of thumb that smooth gradual rolloffs should sound good but responses with peaks will tend to sound boomy. This is not actually because of the frequency response, it is because of the TIME response (ringing).
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