Build 15" or 18" sub... or stand pat? - Page 2 - AVS Forum | Home Theater Discussions And Reviews
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post #31 of 40 Old 01-23-2019, 08:17 AM - Thread Starter
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Originally Posted by markg35 View Post
It's not necessarily a mistake.Lots of us have sealed.If space is the main issue it make sense.As others have said,you could build a Martycube.It's very slightly larger than the sealed flatpacks.I'm not sure how much of a difference it would make compared to a 4-5 cu sealed version.I'm curious as that would be my upgrade path(if it is much of an upgrade).

Sealed will need more power though.Get an iNuke 6000 or something with similar power.Especially if you have any thoughts of ever building a second sub.
OK, thanks. I think I'm OK then. I've got a Crown 2502 on order and I *do* plan to add a 2nd UM-18
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post #32 of 40 Old 01-23-2019, 08:41 AM
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Originally Posted by kennethav View Post
I was planning to do a sealed box. Is that a mistake? My understanding is that I'll get a smoother response curve with sealed, and can always add more if I want more output. Maybe the sealed will require more power to drive?
Sealed is fine (I have two sealed 18"s). It's just that you said your builder was going to make a "front-ported" 4cuft enclosure so I thought it would be ported. That's too small for a ported 18" but perfect for sealed. I think you meant "front-firing"; just a misunderstanding.
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post #33 of 40 Old 01-23-2019, 08:44 AM - Thread Starter
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Originally Posted by jcmccorm View Post
Sealed is fine (I have two sealed 18"s). It's just that you said your builder was going to make a "front-ported" 4cuft enclosure so I thought it would be ported. That's too small for a ported 18" but perfect for sealed. I think you meant "front-firing"; just a misunderstanding.
Ah yeah, my mistake. Front-firing, not front-ported.
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post #34 of 40 Old 01-23-2019, 09:27 AM
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Originally Posted by kennethav View Post
I was planning to do a sealed box. Is that a mistake? My understanding is that I'll get a smoother response curve with sealed, and can always add more if I want more output. Maybe the sealed will require more power to drive?


Driver dependent really. Also depends a lot on your room and EQ.


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post #35 of 40 Old 02-11-2019, 05:36 PM - Thread Starter
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OK, so I went ahead with a pair of sealed (pine plywood), 4 ft^3 cabs for my UM-18s. They sound pretty good, but I'm getting a sharp dropoff under 40hz (see attached graph). I don't think it's a problem with placement, since the graph shows both subs with the same pattern.

Did I make a mistake going with sealed? I've seen others getting strong response in the 20-40hz with the same setup. Or maybe Audyssey is doing something to limit 20-40hz?
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post #36 of 40 Old 02-11-2019, 06:07 PM
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Quote:
Originally Posted by kennethav View Post
OK, so I went ahead with a pair of sealed (pine plywood), 4 ft^3 cabs for my UM-18s. They sound pretty good, but I'm getting a sharp dropoff under 40hz (see attached graph). I don't think it's a problem with placement, since the graph shows both subs with the same pattern.

Did I make a mistake going with sealed? I've seen others getting strong response in the 20-40hz with the same setup. Or maybe Audyssey is doing something to limit 20-40hz?
A few thoughts:

Disable Audyssey when taking measurements.

For subwoofer-only measurements, you want to run from 10 - ~200Hz. The Hz axis is fine at 5Hz increments.

Are your measurements from the MLP or nearfield? Try measuring from 3 ft, with the mic pointing straight at the center of the cone, with the subwoofer sitting in the middle of whatever room you're measuring them in.

What mic are you using?

Are the cabs 4ft^3 net? Subtracting for bracing, driver displacement, etc.
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Sub builds: Yet another Infinity 1260 build | Twins! | Modified V.B.S.S. build | UM12-22 builds | AV stand and sealed UM18s

Speaker builds: DIYSG HTM-10 build | DIYSG Volt-6 build | DIYSG Fusion-8 builds
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post #37 of 40 Old 02-11-2019, 06:12 PM
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Do you have any high pass filters enabled (check the XLS2502)?
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post #38 of 40 Old 02-11-2019, 07:05 PM - Thread Starter
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Quote:
Originally Posted by smcmillan2 View Post
A few thoughts:

Disable Audyssey when taking measurements.

For subwoofer-only measurements, you want to run from 10 - ~200Hz. The Hz axis is fine at 5Hz increments.

Are your measurements from the MLP or nearfield? Try measuring from 3 ft, with the mic pointing straight at the center of the cone, with the subwoofer sitting in the middle of whatever room you're measuring them in.

What mic are you using?

Are the cabs 4ft^3 net? Subtracting for bracing, driver displacement, etc.
Original measurements were at the MLP with a UMIK-1. Sub is 4ft^3 minus driver displacement... maybe they should be a bit bigger? I've got 4 lbs of polyfill contained in some pillow cases inside. Seems pretty full to me... maybe that's a problem?

I re-ran the measurements nearfield as you suggested, without Audyssey. And.... the big problem is my couch

Did I mention the subs are directly behind the couch?

Just for yuks, I also re-ran it the same way, but with the couch between the mic and the sub. Looks like I'm losing 10db in the 20-40hz range.

This is great stuff... thanks! The bad news is that there's no other good place to put two monster subs.
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post #39 of 40 Old 02-17-2019, 11:27 AM
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Quote:
Originally Posted by kennethav View Post
I was planning to do a sealed box. Is that a mistake? My understanding is that I'll get a smoother response curve with sealed,
Depends on what you want. Sealed gives smoother rolloff. Ported will go a little lower all else being equal and then rolloff quicker. Sealed boxes also tend to be smaller.

If bad sound were Faital, good sound would be almost impossible
Killed two Mach5 21s and three UM-18s (and counting?)
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post #40 of 40 Old 02-17-2019, 11:30 AM
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Originally Posted by jcmccorm View Post
Is this for an 18" driver? 4cuft seems too small for a ported box.
Depends on the driver and T/S params.

If bad sound were Faital, good sound would be almost impossible
Killed two Mach5 21s and three UM-18s (and counting?)
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