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Discussion Starter #1 (Edited)
Hi all,
First off, I haven't built any speaker projects for over 20 years. So I'm waaay behind the curve on the new advances and tricks of speaker building.
PLEASE - I am more then open to build recommendations and insight.

Don't know why, but I got the urge to build a subwoofer project.
I tried to talk myself out of it, ...but here I am.


I dove in and did a lot of reading on what other people were recommending, and I decided to use the UM18-22 driver.
During my research I read countless threads of people buying the 4.0 cu ft cabinet from PE, and claim they're ecstatic with the results.
Although, when I plug the driver into WinISD with a 4.0 sealed cabinet - the graph doesn't seem impressive - when compared to vented.


Vented enclosures provide a large advantage in the bottom end.
See the WinISD SPL model for my point:

Blue is the 4.0 cu ft sealed box.
Red is 14 cu ft vented, and the green is various sizes of vented cabinets for comparison.
(All are powered at 500W. All vented cabinets have a high-pass 13hz filter)

The 14 cu ft vented cabinet (red line) has a 9db advantage over the 4.0 cu ft sealed cabinet (blue line) at 20 hz.
A 9 db advantage at 20 hz!!!!!! That's huge!!! And the F3 drop-off goes from (28 hz, sealed) down to (15 hz, vented).
And that's *without* any amplifier low-end boost compensation.


The cone excursion is fine, and port velocity stays within the 110 ft/s recommended limit (for 14 cu ft cabinet - or smaller).



So what gives?

Based on the WinISD outputs, why would someone choose sealed over vented?
I understand the PE flat-pack cabinet is easy to assemble and relatively small. (Easy, Simple, and good WAF)
The downside to vented cabinets are that they are much larger. Is the cabinet size the only reason?


How do the sealed cabinet folks compensate for such a drastic disadvantage?





Thanks in advance.
 

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So what gives?

Based on the WinISD outputs, why would someone choose sealed over vented?
I understand the PE flat-pack cabinet is easy to assemble and relatively small. (Easy, Simple, and good WAF)
The downside to vented cabinets are that they are much larger. Is the cabinet size the only reason?


How do the sealed cabinet folks compensate for such a drastic disadvantage?
Thanks in advance.
Sealed will almost always be smaller than ported and that may be needed in a given space. EQ and power as well as careful placement, using multiples etc can make up for it. Typically sealed speakers roll of in the LF at a slower rate, 12dB/oct and cabin gain in smaller rooms will bring up the low end so less EQ and power is needed.


Ported have an advantage in the fairly narrow bandwidth of the Helmholtz resonance; they are NOT more efficient than sealed, except in this narrow BW. They're larger physically, roll off at a faster rate, 24dB/oct and they really need an electrical 2nd order filter below tune to ensure that the driver does not go into over excursion with loud signal below the tune of the enclosure. Do this and you have an effective 36dB/oct roll off, so can have a narrower useful bandwidth. There's lots below 20Hz in a lot of mainly action movies.
 

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Sealed will almost always be smaller than ported and that may be needed in a given space. EQ and power as well as careful placement, using multiples etc can make up for it. Typically sealed speakers roll of in the LF at a slower rate, 12dB/oct and cabin gain in smaller rooms will bring up the low end so less EQ and power is needed.


Ported have an advantage in the fairly narrow bandwidth of the Helmholtz resonance; they are NOT more efficient than sealed, except in this narrow BW. They're larger physically, roll off at a faster rate, 24dB/oct and they really need an electrical 2nd order filter below tune to ensure that the driver does not go into over excursion with loud signal below the tune of the enclosure. Do this and you have an effective 36dB/oct roll off, so can have a narrower useful bandwidth. There's lots below 20Hz in a lot of mainly action movies.
The frequency where the different slopes meet is around 11hz. The ported wins everywhere it really matters.

I built a UM18 sealed for an 1800 cu ft space, and between AccuEQ room correction and manual EQ, I was able to get a pretty flat response down to around 10hz at 105db at the MLP.

I have to shove a lot of power into the sub at the low end though, and I suspect I'd get a lot more output from 15ish hz on up if I went ported. Do I need that? Questionable.
Do I want that? Yes.

Another consideration is bass shakers, and the boss platform which is discussed over at the hideaway theater thread.

Those can pick up where a ported drops off around 20 Hertz and provide tactile response to your seat down to like 5 hz.

You can't hear below 20 Hertz anyway so energizing the room with those frequencies doesn't make much sense to me.

If your room is much larger than 2000 cubft, or has many openings, it behooves you to do the ported sub.

Sealed subs quickly become ineffective in larger spaces.









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Based on the WinISD outputs, why would someone choose sealed over vented?
I understand the PE flat-pack cabinet is easy to assemble and relatively small. (Easy, Simple, and good WAF)
The downside to vented cabinets are that they are much larger. Is the cabinet size the only reason?
You answered your own questions:)
 
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You're on the right track with your modeling and comparisons, OP.

FYI, not that it really matters, but I'd switch your units to mm for excursion and m/s for port velocity, just because that's more standard.

You can use the Max SPL graph to quickly compare max output between alignments, accounting for xmax and max power. That becomes the max headroom graph, essentially, as you can EQ the responses to anything below that, but not above. What it doesn't account for is port compression, which is very important.

To me, the absolute biggest key to ported sub design is maximizing port size, which also means maximizing port length for a given box size and tune. So decide the longest port you're comfortable with from a first port resonance perspective (for me that's about 48"), and make sure you are using all of that length to maximize your port area. Ideally, you can get max port velocity down to 20 m/s or below and then port compression will be a very minor issue and the Max SPL graph for the ported will be quite accurate around tune. Otherwise, the advantage that ported appears to have over sealed becomes partially an illusion, as port compression will not allow the ported sub to hit the SPL levels that the model shows.

Using your example of 14cf and 16.5Hz tune, using a 10" port @ 48" long, max port velocity is only 15m/s at 15.6Hz while producing 113dB natively. At that size box you can easily lower tune even further while maintaining healthy port velocity. For example, drop the port size to 8" @ 48" and tune drops down to 13.4Hz while keeping max port velocity still at only 18 m/s at 12.3Hz while producing 108dB. That's a very compelling option IMO if you value that extra extension. At that point ported is able to match sealed even down at 9Hz while having its huge advantage between 10-30Hz. Note: I am using round ports for these examples but you can just as easily do a slot port or square ports and do the same port area and make putting bends in the port much easier.
 

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Something else to consider when reading another persons impressions about a particular driver. You have no idea what that person has listened to. If they are used to a 10" Polk subwoofer, a simple 15" ported DIY will blow their mind. If they are used to HS24s, they will be thoroughly unimpressed with a sealed 18". (in general) My personal opinion, if you're looking for over the top output, like most of this community, go as large of a driver in as large a cabinet that you can fit in your space. Have fun!
 

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I 100% agree with the above post:)
 

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Yeah, the 4cf sealed UM18 flatpacks (and other sealed subs) are a great option in smaller rooms with good gain, where the native in-room response ends up pretty flat or rising without much low-end boost. In other rooms, like mine, I'd need 8 or 16 of them to get any kind of good output down at 10Hz. The two flatpacks I added to my system added next to nothing because my ported monsters have way more output down low and I need every bit of it in my room. The flatpack subs are essentially speaker stands that look like subwoofers. :)
 

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Something else to consider when reading another persons impressions about a particular driver. You have no idea what that person has listened to. If they are used to a 10" Polk subwoofer, a simple 15" ported DIY will blow their mind. If they are used to HS24s, they will be thoroughly unimpressed with a sealed 18". (in general) My personal opinion, if you're looking for over the top output, like most of this community, go as large of a driver in as large a cabinet that you can fit in your space. Have fun!
What I find when others give listening impressions is they normally describe their room modes. You'll hear terms like boom and quick and what ever else that is more so do with their room than the sub.


I understand that a majority of the DIY community won't be measuring their room or applying DSP (or both) to their set up, but most times an opinion on a sub is characterized by their lack of understanding with how it interacts with their given space.


OP - as others have said you are on the right track and also have the right assumptions.


I'd also mention that sealed is the safest way to build a sub and is the best for a person who is less interested in the details. Take the UM18 for example, it'll be really hard to break it on a standard 15amp circuit in a 4.0 cu/ft sealed box. Its response is also incredible in that alignment too.
 

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I'd also mention that sealed is the safest way to build a sub and is the best for a person who is less interested in the details. Take the UM18 for example, it'll be really hard to break it on a standard 15amp circuit in a 4.0 cu/ft sealed box. Its response is also incredible in that alignment too.
Actually, I'd argue that sealed often requires more paying attention to the details rather than simply running room correction, because it may require low-end boost to properly utilize the sub's capabilities, which room correction isn't going to apply. And once we start adding low-end boost, we need to really know what we're doing to make sure we aren't using up too much headroom for a user's particular listening levels.

Sure, ported needs a proper HPF, but that's really simple to add, and then it's pretty much just as safe and hard to break as a sealed UM18. Then someone just running room correction has a much better change of getting a good EQed response with the extension the sub is capable of. And the additional headroom of the ported serves as additional protection.

The 4cf sealed response is "incredible"? What's incredible about it? It's a standard sealed response, it's pretty much the bottom of the barrel response. Sure, it can work out well in the right room, but there's nothing incredible about it IMO.
 

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Actually, I'd argue that sealed often requires more paying attention to the details rather than simply running room correction, because it may require low-end boost to properly utilize the sub's capabilities, which room correction isn't going to apply. And once we start adding low-end boost, we need to really know what we're doing to make sure we aren't using up too much headroom for a user's particular listening levels.

Sure, ported needs a proper HPF, but that's really simple to add, and then it's pretty much just as safe and hard to break as a sealed UM18. Then someone just running room correction has a much better change of getting a good EQed response with the extension the sub is capable of. And the additional headroom of the ported serves as additional protection.

The 4cf sealed response is "incredible"? What's incredible about it? It's a standard sealed response, it's pretty much the bottom of the barrel response. Sure, it can work out well in the right room, but there's nothing incredible about it IMO.

Show me another sub that is $300 that presents a flat response down to the 30’s with the same sensitivity to ULF in a similar sized box.

We can nitpick everything down to a specific and say something is more dangerous. The fact is, by itself, on a 15amp circuit and a typical amp you won’t destroy a sealed UM18. If you start including boost, the most dangerous thing to do would be to overly boost mid bass frequencies on the UM as that’ll blow the voice before excursion ever would.


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Show me another sub that is $300 that presents a flat response down to the 30’s with the same sensitivity to ULF in a similar sized box.
We aren't talking about the UM18 vs another driver. I love the UM18 for the money in any alignment. We're talking about the UM18 sealed vs ported. You said the response sealed was incredible, I questioned why you would say that, it's a pretty standard sealed response, nothing special. If you are just talking about the UM18 in general, then I think we both agree it's great for the money.

We can nitpick everything down to a specific and say something is more dangerous. The fact is, by itself, on a 15amp circuit and a typical amp you won’t destroy a sealed UM18. If you start including boost, the most dangerous thing to do would be to overly boost mid bass frequencies on the UM as that’ll blow the voice before excursion ever would.
Right, and the same exact points stand with a ported UM18, as long as it has a proper HPF (which I consider simple enough for anyone building a sub), but with even more headroom/safety factor where it has an advantage over sealed. You said you think sealed is a simpler option and gave some reasons why. I responded that I actually think ported is simpler and gave the reasons why.

I think it's an often overlooked drawback of trying to use sealed subs in the simplest room correction only case, it's very dependent on the in-room native response shape being flat enough that room correction will do its thing with it. And then if not, even if the user is willing and able to give it some low-end boost to flatten it out before running room correction, there are some important headroom considerations to make there, it becomes more of an advanced exercise that requires balancing extension, capabilities, listening level. As opposed to a ported scenario where the native in-room response is far more likely to be flat or rising, and simply running room correction more often results in a nice flat response with full extension. It's not necessarily a deal maker or breaker, but like I said, I think it's an often overlooked part of running room correction only with sealed subs.
 

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You said the response sealed was incredible, I questioned why you would say that, it's a pretty standard sealed response, nothing special.
This is where I disagree. For sealed that is.

It’s special because there aren’t a whole mass of sub drivers available that show a good native response in a sealed box, normally they have a huge arc. In the case of the UM, you don’t start the drop off till the mid 30’s, in a box where the QTC isn’t .707 either. Technically the driver does doesn’t need the technical .707 to function properly but that’s another discussion.

Either way, my praise for it is that it doesn’t show typical early sealed roll off, still maintains great great ULF sensitivity and has a balanced box size. I also do not think this typical of sealed sub drivers either, but I could be wrong!


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Snipped in many places.
The ported wins everywhere it really matters.
No, as I said, it depends on what you're trying to accomplish and the limitations such as enclosure size etc you may be able to live with.
My comments you quoted, were general in mature and not specific to the UM18


Another consideration is bass shakers
Those can pick up where a ported drops off around 20 Hertz and provide tactile response to your seat down to like 5 hz.
See next comment.

You can't hear below 20 Hertz anyway so energizing the room with those frequencies doesn't make much sense to me.
You've obviously never felt it; it's not the same as shakers. I have Crowsons.

If your room is much larger than 2000 cubft, or has many openings, it behooves you to do the ported sub.
My current room is 1830cf and my four sealed FTW21s go deep and loud, and the room has to large non sealable openings.

Sealed subs quickly become ineffective in larger spaces.
Meh. Try nearfield.
 

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Show me another sub that is $300 that presents a flat response down to the 30’s with the same sensitivity to ULF in a similar sized box.
It’s special because there aren’t a whole mass of sub drivers available that show a good native response in a sealed box, normally they have a huge arc. In the case of the UM, you don’t start the drop off till the mid 30’s, in a box where the QTC isn’t .707 either. Technically the driver does doesn’t need the technical .707 to function properly but that’s another discussion.

Either way, my praise for it is that it doesn’t show typical early sealed roll off, still maintains great great ULF sensitivity and has a balanced box size. I also do not think this typical of sealed sub drivers either, but I could be wrong!
Well, there aren't many $300 drivers in general, but here are some in that range off the top of my head that work well in 4cf sealed or smaller:
UM18 $325
Fi HT-1 $299
SI SQL-15 $320
SI SQL-12 $290

In any case, to be clear, I'm a HUGE fan of the UM18 for the money, in any alignment, including sealed. I recommend it first to everyone I design a sub for, for that reason. I just don't see anything special or magical about its sealed response. It's a pretty typical low-sensitivity high-excursion driver sealed response. Are you comparing it to high-sensitivity PA drivers? Well, that's a different animal. The Fi HT-1 is probably its closest competition on the market, with it being $299 and being an 18, and it has a very similar response.
 

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Snipped in many places.No, as I said, it depends on what you're trying to accomplish and the limitations such as enclosure size etc you may be able to live with.
My comments you quoted, were general in mature and not specific to the UM18


See next comment.

You've obviously never felt it; it's not the same as shakers. I have Crowsons.

My current room is 1830cf and my four sealed FTW21s go deep and loud, and the room has to large non sealable openings.

Meh. Try nearfield.
Oh you sure got me good!

Ill be more specific.

The ported box with a um18 will win in SPL output at every *frequency* that really matters, over the sealed.
The modeled response demonstrates that.
They are equal at about 11 Hertz.
Above that the ported has more output.

I understand there are other considerations, I was strictly talking frequency response.

I said one option is adding tactile to supplement ported subs, and it is. If that's not your preference that's fine. Many sealed subs or running nearfield is not an option for many, including myself.

It doesn't make sense to me to load a room with many sealed subs and immense amounts of power when you can replace that with a single ported sub and some tactile response.

Maybe it makes sense for you but not for me, and not for most other people.

The OP is asking about a single sub, and in a larger room, sealed subs placed anywhere EXCEPT nearfield is going to yield completely inadequate performance.

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the HT-1 does have more output than the UM18 above 35ish hertz but does drop off earlier(still ends up with the same low end output)
Thanks, that graph proves my point. There's nothing special about the response, they are almost identical, the HT-1 just looks to be about 1dB more sensitive up top.
 

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Well, there aren't many $300 drivers in general, but here are some in that range off the top of my head that work well in 4cf sealed or smaller:
UM18 $325
Fi HT-1 $299
SI SQL-15 $320
SI SQL-12 $290

In any case, to be clear, I'm a HUGE fan of the UM18 for the money, in any alignment, including sealed. I recommend it first to everyone I design a sub for, for that reason. I just don't see anything special or magical about its sealed response. It's a pretty typical low-sensitivity high-excursion driver sealed response. Are you comparing it to high-sensitivity PA drivers? Well, that's a different animal. The Fi HT-1 is probably its closest competition on the market, with it being $299 and being an 18, and it has a very similar response.
The SQL-15 doesn't sim as well, but this is kind of what I'm talking about drivers in sealed alignment. It drops off early in the 80's and has a shallow slope to eventually catch up to the 18's. There are Klippel floating around though that pretty much confirms the T/S they posted. To be clear, I'm really excited about this driver, very excited. It has the headroom to boost down low and really kickass.

I admit I did forget about the Fi, but the Fi rocks a relatively weak motor with no shorting rings, still if it does measure similar to the sims then it does indeed beat the UM18. So theres 2 drivers with similar responses in smaller boxes, unless I am forgetting anymore. To me that is a pretty awesome response. Remember you are challenging my opinion that the UM18 has an 'incredible' response in a sealed alignment, I never said it was unique or better than a ported alignment. We have come to find out that Fi has a similar looking driver, and if I remember correctly that was their intent. It also bothers me that Fi Doesn't post Le either and their CMS numbers are commonly different then whats found ….

I did consider PA drivers in sealed boxes but there are only two that I know of that has a decent response in sealed boxes and they aren't exactly priced in the ranges we are discussing so no, I'm not considering those.

I was going to buy the SQL-15, it is in my future but I am deploying … yet again so that's a plan I have to hold off on. I was hoping to measure it in a fairly massive sealed box to see how it would handle north of 1000w and hit xmax. This would eventually go into my Wrangler as I don't need to upgrade from my 21's at home.

Also don't forget, the Fi has the SSD's (great driver), PSI has … something … I'll remember it I'm sure and there is of course Sundown. Now I never said specifically 18" but I wanted it compared to a driver that is $300 (or similar) in a similar sealed box. To me it is very nice response.
 

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Discussion Starter #20 (Edited)
Wow,

What an awesome community! Lots of great insight and experiences.
So, just to clarify - yes, this is for home theater purposes - in a open large (800-1000) sq ft room with typical 8' ceilings.

Given the discussion, each design is appropriate for difference scenarios. ( correct me if I'm wrong )

Sealed subs are more appropriate when:
1) Smaller boxes are required, 2) Used in smaller rooms, 3) Sealed cabinets helps to limit cone over-excursion, 4) Sealed unfortunately constricts the (SPL) output of lower frequencies.
***The constricted lower frequencies can be compensated partially by amplifier boost, or by having (more) speakers.

Ported subs are more appropriate when:
1) Larger boxes are acceptable, 2) Used in larger rooms, 3) More output at lower frequencies, 4) Ported cabinets must be managed to avoid cone over-excursion.
***Cone-excursion can be managed via HPF or reducing amplifier size (less wattage).




Different people have different goals regarding "Sub-woofers".
I consider the entire purpose of a sub-woofer is to maximize the production of lower frequencies (below 35-40 hz) at sufficient SPL levels with a flat response.

If the goal is 35-40hz and up - then (in my opinion) any box-store subwoofer is the easy 80% solution.
So when I see the UM18 in a 4.0 cu ft sealed box, with a F3 roll-off of 30 hz - I'd consider that mostly equivalent to store-bought sub-woofer performance.
To clarify - If you're happy with sealed subs - then more power to you.
Maybe there's more to it. I just don't get it.


Looks like I'll be trying a ported design.
Ok - more questions......


-Can you please discuss more about 'port-compression'?
I have the understanding that the port does 2 things. 1) It's TUNED to a certain frequency, and 2) it's for air intake/exhaust due to the driver displacement.
The port air-velocity should try to be minimized - or you'll hear 'chugging'. (110 ft/s or less?) You can reduce air-velocity with more vents - or larger diameter vents.
I've never seen 'port-compression' referenced.



-I could also use some insight regarding 'room-gain'.
My room is large and open, ...although the theater (big screen) is in a corner of the room - not the whole thing.
I have (0) knowledge on this, but seen it discussed a lot - and it seems important.
How do I understand this, and how does it impact sub-woofer designs?
Please use small words. : )


-My 14 cu ft ported design has an inherently flat response down to 16 hz (+/- 3db).
I am mostly new to DSP's. Is there any point in a DSP?
I understand them as 'digital equalizers' to custom set for unique rooms interactions. Yes?
Good/bad/unnecessary?


Thanks.
 
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