Nearfield Subwoofer (under couch): need advice! - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 22 Old 10-21-2017, 03:06 PM - Thread Starter
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Nearfield Subwoofer (under couch): need advice!

Hey

I recently got the idea of building a platform to raise my couch (cant lower the tv) for a better viewing angle. This gives me the opportunity to use it as a nearfield subwoofer enclosure. It would measure 200 cm x 30cm x 120cm, but I could adjust that if necessary. Would this be a decent size? Could I achieve sub 20hz frequencies with 2 18" (or 21") woofers? Would use it up to 35hz and cross over to my other sub. If so, how would I calculate the correct measurements. What kind speaker specs should I look for? Things like Qes and Xmax or?

Thanks in advance!
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post #2 of 22 Old 10-21-2017, 05:03 PM - Thread Starter
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Those look like some pretty badass drivers, would my setup work better than the one described there? To be precise, would I be in the advantage because of my much larger volume (18 ft^3 vs 5.5 ft^3)?
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post #3 of 22 Old 10-21-2017, 05:25 PM
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I replied to you here. https://www.avsforum.com/forum/155-di...l#post54994464

Maybe someone else will know some good drivers that you can get. You said you cant get Dayton Ultimax, correct?

"Cool, I have thought about doing this but with a nearfield behind me, I don't need it right now in this room.

Do you want to go sealed or ported? It looks like you will have around 18cf to work with. So far I found 2 of the brands that you can get and both are pretty close output wise in either sealed or ported. Faital 18xl1800 and Radian 2218. The only thing is depth wise they might be pushing the depth/height of 30cm with the 18x1800(dept of 23cm approx).

Rough external enclosure dimensions. Putting this here for my reference. 18cf internal rough.
Width 78"
Box Height 11"
Box Depth 47"

I have to look into it more when I have the energy. Also reading about the Radian it sounds like it doesn't meet the specs in real-world use from the little I read on it. I would lean towards the Faital as of now from what I read it is highly regarded. I'll try and look into it more another time.

But you have plenty of space to go ported but sealed would work well if you want to output into the single digits. Being right under you, you should feel the sealed into the single digits. I have a UM18 behind me and I am on a suspended floor and I get feel from the sub down to 6-7hz and you should get similar output with the 18x1800 from what I am seeing. So I think you could expect something similar but is dependent on many factors like the construction of the seating. Each person sensitivity to bass etc.

Brands @Droogne can get. https://www.avsforum.com/forum/attach...2&d=1507982821 "

HTPC, Sony 40es, 120" Silver Ticket, 7702mkii, Sunfire Amp 225w, JBL 590, JBL 520

PSA XS30, Seaton Submersive, 2 Um-18 8cf sealed, Outlaw Ultra x 12, Kappa Pro 18LF, BFM Tuba 60 horn, B&C 18TBW100 6cf 41hz, 34hz, 28hz tune

iNuke 3000 & 6000 DSP's, Crowson Motion Actuator

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post #4 of 22 Old 10-21-2017, 05:47 PM
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The Stereo Integrity ht18 would be perfect for this in 4 cubes sealed firing right up into the bottom of the couch. @Scott Simonian will be so proud to hear about this...
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post #5 of 22 Old 10-21-2017, 06:50 PM
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Originally Posted by d_c View Post
The Stereo Integrity ht18 would be perfect for this in 4 cubes sealed firing right up into the bottom of the couch. @Scott Simonian will be so proud to hear about this...
Even better the 24" I don't think he has access to SI though. He posted in another thread that he only has access to a small number of brands in the country he is in.


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post #6 of 22 Old 10-22-2017, 03:33 AM - Thread Starter
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Originally Posted by bscool View Post
I replied to you here. https://www.avsforum.com/forum/155-di...l#post54994464

Maybe someone else will know some good drivers that you can get. You said you cant get Dayton Ultimax, correct?

"Cool, I have thought about doing this but with a nearfield behind me, I don't need it right now in this room.

Do you want to go sealed or ported? It looks like you will have around 18cf to work with. So far I found 2 of the brands that you can get and both are pretty close output wise in either sealed or ported. Faital 18xl1800 and Radian 2218. The only thing is depth wise they might be pushing the depth/height of 30cm with the 18x1800(dept of 23cm approx).

Rough external enclosure dimensions. Putting this here for my reference. 18cf internal rough.
Width 78"
Box Height 11"
Box Depth 47"

I have to look into it more when I have the energy. Also reading about the Radian it sounds like it doesn't meet the specs in real-world use from the little I read on it. I would lean towards the Faital as of now from what I read it is highly regarded. I'll try and look into it more another time.

But you have plenty of space to go ported but sealed would work well if you want to output into the single digits. Being right under you, you should feel the sealed into the single digits. I have a UM18 behind me and I am on a suspended floor and I get feel from the sub down to 6-7hz and you should get similar output with the 18x1800 from what I am seeing. So I think you could expect something similar but is dependent on many factors like the construction of the seating. Each person sensitivity to bass etc.

Brands @Droogne can get. https://www.avsforum.com/forum/attach...2&d=1507982821 "
Whoa thanks for the suggestions! I can get the Ultimax (see thumbnail), and I have found some shops in neighbouring countries that could sell me the Radian and Faital. I also have the possibility to buy the 21" B&C 21SW152 second hand.

At the moment I'm not sure if I'd wanna go ported or sealed, but both could work. Ported would look hella cool though ! Might be a lot more complicated to build I fear.. Also to save me some money at the moment, I was thinking about building the cabinet to hold 2, but only cut out 1 of the holes. Then when I save some more money I could buy the second woofer.. This would give me the opportunity to buy a really good, but expensive (too expensive for me to afford twice for example) woofer. I could maybe even try to do this with triple woofers. The ultimax does seem to perform really well for a reasonable price: "Vented (infra-sub): 12 cubic ft. (net internal, not including driver or vent) tuned to 15.5 Hz, with 3 flared vents 4" diameter by 32" long, for an f3 of 15 Hz"

In my search for woofers I was wondering what I should look for.. sometimes they sell really really cheap B-stock woofers, I just bought a RCF LF18X400 for 70% discount, and I was hoping to be able to do something like this again. What specs should I look for? I also downloaded WinISD, but I'm still figuring it out.

I also included some pics: all the 21" woofer I can get my hands on in my local store, another big store which sells a lot of 18" woofers and thirdly the list of Dayton woofers (including the Ultimax).

Thanks!
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post #7 of 22 Old 10-22-2017, 03:36 AM - Thread Starter
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Even better the 24" I don't think he has access to SI though. He posted in another thread that he only has access to a small number of brands in the country he is in.

I had already contacted them and they can ship! Will be pretty expensive though.. the driver itself is darn pricey.
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post #8 of 22 Old 10-22-2017, 03:57 AM - Thread Starter
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The Stereo Integrity ht18 would be perfect for this in 4 cubes sealed firing right up into the bottom of the couch. @Scott Simonian will be so proud to hear about this...
I think I got the idea from a post of him! Are you proposing to cut the riser in 4, like 4 separate cubes? Cause I was already thinking something like that, as it would be hell of a lot easier to move. Maybe not in 4, but in 3 or 2. I also think the platform should be a bit longer, more like 7ft. 4inches. This could give me 2x310L cubes, 3x 200L cubes or 4x 150L cubes. What would be a good combo? I wouldnt mind going with some smaller woofers to accommodate this.

Orrrrr, would I be able to make the cabinet in a way that I could easily (in a few hours) split it in 2? That way I would have 2 semi squared boxes open on 1 side. I would then glue them together, and remove the glue (with a saw) when I want to disassemble. That way I could move a lot easier. Or would I never be able to completely seal this construction?

Last edited by Droogne; 10-22-2017 at 04:08 AM.
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post #9 of 22 Old 10-22-2017, 05:14 AM
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I would build a single large box because I think it would be easier, and the 18" Ultimax sealed would be great
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post #10 of 22 Old 10-22-2017, 09:05 AM - Thread Starter
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I would build a single large box because I think it would be easier, and the 18" Ultimax sealed would be great
How realistic is to disassembly a large box like this ? The pannels by them self will be a lot more easy to move. And do you think the box size I proposed could work with both 1 or 2 (or 3) woofers? That way I could start with 1 and cut the holes for a new woofer later on.

EDIT: Would you recommend sealed above ported? The recommended volume for a vented Ultimax (f3: 15hz) is 340L, which means I could get 2 in there right? Would it matter that the box is twice as big as the recommended volume if I'd only use one (I'm guessing I'd have to modify the ports?)?

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post #11 of 22 Old 10-22-2017, 11:01 AM - Thread Starter
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Is there a rule to bracing? How would I go about doing this for this kind of project?
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post #12 of 22 Old 10-23-2017, 01:12 AM
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Originally Posted by Droogne View Post
Whoa thanks for the suggestions! I can get the Ultimax (see thumbnail), and I have found some shops in neighbouring countries that could sell me the Radian and Faital. I also have the possibility to buy the 21" B&C 21SW152 second hand.

At the moment I'm not sure if I'd wanna go ported or sealed, but both could work. Ported would look hella cool though ! Might be a lot more complicated to build I fear.. Also to save me some money at the moment, I was thinking about building the cabinet to hold 2, but only cut out 1 of the holes. Then when I save some more money I could buy the second woofer.. This would give me the opportunity to buy a really good, but expensive (too expensive for me to afford twice for example) woofer. I could maybe even try to do this with triple woofers. The ultimax does seem to perform really well for a reasonable price: "Vented (infra-sub): 12 cubic ft. (net internal, not including driver or vent) tuned to 15.5 Hz, with 3 flared vents 4" diameter by 32" long, for an f3 of 15 Hz"

In my search for woofers I was wondering what I should look for.. sometimes they sell really really cheap B-stock woofers, I just bought a RCF LF18X400 for 70% discount, and I was hoping to be able to do something like this again. What specs should I look for? I also downloaded WinISD, but I'm still figuring it out.

I also included some pics: all the 21" woofer I can get my hands on in my local store, another big store which sells a lot of 18" woofers and thirdly the list of Dayton woofers (including the Ultimax).

Thanks!
One of the main things to look for is Xmax since you want this for the low-frequency output, around 20mm or more. Also, cone area so 18" or 21" drivers but most of them will be too deep for what you want to do. I would think the UM18 or SI HT18 will be the best output for your $$ options but both are going to be tight to fit in an enclosure with the 30cm height limited you wanted, they might work but it will be close.

HTPC, Sony 40es, 120" Silver Ticket, 7702mkii, Sunfire Amp 225w, JBL 590, JBL 520

PSA XS30, Seaton Submersive, 2 Um-18 8cf sealed, Outlaw Ultra x 12, Kappa Pro 18LF, BFM Tuba 60 horn, B&C 18TBW100 6cf 41hz, 34hz, 28hz tune

iNuke 3000 & 6000 DSP's, Crowson Motion Actuator
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post #13 of 22 Old 10-23-2017, 01:27 AM - Thread Starter
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Originally Posted by bscool View Post
I replied to you here. https://www.avsforum.com/forum/155-di...l#post54994464

Maybe someone else will know some good drivers that you can get. You said you cant get Dayton Ultimax, correct?

"Cool, I have thought about doing this but with a nearfield behind me, I don't need it right now in this room.

Do you want to go sealed or ported? It looks like you will have around 18cf to work with. So far I found 2 of the brands that you can get and both are pretty close output wise in either sealed or ported. Faital 18xl1800 and Radian 2218. The only thing is depth wise they might be pushing the depth/height of 30cm with the 18x1800(dept of 23cm approx).

Rough external enclosure dimensions. Putting this here for my reference. 18cf internal rough.
Width 78"
Box Height 11"
Box Depth 47"

I have to look into it more when I have the energy. Also reading about the Radian it sounds like it doesn't meet the specs in real-world use from the little I read on it. I would lean towards the Faital as of now from what I read it is highly regarded. I'll try and look into it more another time.

But you have plenty of space to go ported but sealed would work well if you want to output into the single digits. Being right under you, you should feel the sealed into the single digits. I have a UM18 behind me and I am on a suspended floor and I get feel from the sub down to 6-7hz and you should get similar output with the 18x1800 from what I am seeing. So I think you could expect something similar but is dependent on many factors like the construction of the seating. Each person sensitivity to bass etc.

Brands @Droogne can get. https://www.avsforum.com/forum/attach...2&d=1507982821 "
Pretty expensive considering gthe Ultimax is only 420 a piece all inclusive.
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post #14 of 22 Old 10-23-2017, 03:03 AM - Thread Starter
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Originally Posted by Droogne View Post
Whoa thanks for the suggestions! I can get the Ultimax (see thumbnail), and I have found some shops in neighbouring countries that could sell me the Radian and Faital. I also have the possibility to buy the 21" B&C 21SW152 second hand.

At the moment I'm not sure if I'd wanna go ported or sealed, but both could work. Ported would look hella cool though ! Might be a lot more complicated to build I fear.. Also to save me some money at the moment, I was thinking about building the cabinet to hold 2, but only cut out 1 of the holes. Then when I save some more money I could buy the second woofer.. This would give me the opportunity to buy a really good, but expensive (too expensive for me to afford twice for example) woofer. I could maybe even try to do this with triple woofers. The ultimax does seem to perform really well for a reasonable price: "Vented (infra-sub): 12 cubic ft. (net internal, not including driver or vent) tuned to 15.5 Hz, with 3 flared vents 4" diameter by 32" long, for an f3 of 15 Hz"

In my search for woofers I was wondering what I should look for.. sometimes they sell really really cheap B-stock woofers, I just bought a RCF LF18X400 for 70% discount, and I was hoping to be able to do something like this again. What specs should I look for? I also downloaded WinISD, but I'm still figuring it out.

I also included some pics: all the 21" woofer I can get my hands on in my local store, another big store which sells a lot of 18" woofers and thirdly the list of Dayton woofers (including the Ultimax).

Thanks!
One of the main things to look for is Xmax since you want this for the low-frequency output, around 20mm or more. Also, cone area so 18" or 21" drivers but most of them will be too deep for what you want to do. I would think the UM18 or SI HT18 will be the best output for your $$ options but both are going to be tight to fit in an enclosure with the 30cm height limited you wanted, they might work but it will be close.
I can change the height if needed, how much inch would you recommend behind the driver at the least? I read 2" somewhere, could this be correct?
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post #15 of 22 Old 10-23-2017, 07:44 AM
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I can change the height if needed, how much inch would you recommend behind the driver at the least? I read 2" somewhere, could this be correct?
I have read 2" also but I think it also depends on the driver but it probably is a good estimate.

Something else you could do if you want to keep the enclosure height at 30 is to have a raised mounting flange/baffle(could be round) where the sub is attached that is raised however much you need be it .75" or 1.5". Kinda like Seaton does with the DS18-12 which is 12.5" deep. This link has pics https://www.avsforum.com/forum/113-su...l#post52913193 so it might make more sense when you see it. This way your seating would be at the height you want and you would just place the sub and flange under the seating where it is not in contact with the seating. It would depend on what your seating looks like underneath if this would work since you would need an open area the size of your flange/baffle so it doesn't contact the seating and it straddles it.

I think you could get by with less than 2"/51mm behind the driver since it doesn't look like the Seaton has 2" going by the depth of 12.5" and take it that includes the surround as you can see in the side pics it is flush with the front baffle.



The UM18 spec sheet says it is 259mm from the top of the mounting flange to the bottom of the magnet, the surround adds approximately another 20mm. Then your enclosure back will be around 19mm then if you give 20mm behind the magnet for airflow will put it at 318mm or 12.5" pretty much what Seaton DS18s depth is.

You will need to double check those numbers as I just did them quickly and also spec sheets are not always accurate/misprint so I would measure the actual driver to make verify.

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I have read 2" also but I think it also depends on the driver but it probably is a good estimate.

Something else you could do if you want to keep the enclosure height at 30 is to have a raised mounting flange/baffle(could be round) where the sub is attached that is raised however much you need be it .75" or 1.5". Kinda like Seaton does with the DS18-12 which is 12.5" deep. This link has pics https://www.avsforum.com/forum/113-su...l#post52913193 so it might make more sense when you see it. This way your seating would be at the height you want and you would just place the sub and flange under the seating where it is not in contact with the seating. It would depend on what your seating looks like underneath if this would work since you would need an open area the size of your flange/baffle so it doesn't contact the seating and it straddles it.

I think you could get by with less than 2"/51mm behind the driver since it doesn't look like the Seaton has 2" going by the depth of 12.5" and take it that includes the surround as you can see in the side pics it is flush with the front baffle.



The UM18 spec sheet says it is 259mm from the top of the mounting flange to the bottom of the magnet, the surround adds approximately another 20mm. Then your enclosure back will be around 19mm then if you give 20mm behind the magnet for airflow will put it at 318mm or 12.5" pretty much what Seaton DS18s depth is.

You will need to double check those numbers as I just did them quickly and also spec sheets are not always accurate/misprint so I would measure the actual driver to make verify.
Hmm.. I 'll definitely check with Dayton themselves to verify the minimum depth, but 320mm is not so much a difference. Those seatonsound subs look gorgeous by the way! What kind of material is that? Also, the UM18 is out of stock till january.. I can wait so it's not that big a problem, but they recommended the Dayton Audio RSS460HO-4 instead. I see the xmax is a lot lower (12 instead of 22). No go, or would this work too?
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What about using passive radiiators? I was just thinking about it as it would look cool, but wouldn't it also help with efficiency and frequency range etc? I'm knew to this kind of calculations, but I think I can manage with 2 Dayton Audio RSS460-PR 18" no? They move enough air and my more complex (although I probably will have made some mistakes) calculations put it at a required 1700g radiator weight (when using this 2x18" PR) which I can meet with the included weights. I would need somebody else to confirm all of this ofcourse if I'd go this way.

Thoughts?
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Hmm.. I 'll definitely check with Dayton themselves to verify the minimum depth, but 320mm is not so much a difference. Those seatonsound subs look gorgeous by the way! What kind of material is that? Also, the UM18 is out of stock till january.. I can wait so it's not that big a problem, but they recommended the Dayton Audio RSS460HO-4 instead. I see the xmax is a lot lower (12 instead of 22). No go, or would this work too?
I would wait for the UM18 over the RSS460 since you are wanting to use them for the low-end output. http://www.data-bass.com/data?page=s...d=116&mset=128 I don't know if you know about databass but they have tested both and the UM18 has more output across the frequency range.

I have never messed with passive radiators. The little I know about them I don't think you would want to use them in this application.

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post #19 of 22 Old 10-23-2017, 11:39 AM
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Not super familiar with them but I "think" they are mainly intended for use when you want a smaller sealed box to behave like a ported box and you are unable to either: make the box bigger, or fit the appropriate size port into your box.

Most here would just build a slot port as its much cheaper to do that then buy multiple passives. IIRC you normally want a passive cone area that is 2 times the surface area of your active driver.

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post #20 of 22 Old 10-23-2017, 01:43 PM - Thread Starter
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Originally Posted by bscool View Post
I would wait for the UM18 over the RSS460 since you are wanting to use them for the low-end output. http://www.data-bass.com/data?page=s...d=116&mset=128 I don't know if you know about databass but they have tested both and the UM18 has more output across the frequency range.

I have never messed with passive radiators. The little I know about them I don't think you would want to use them in this application.
The guys who would sell me the Dayton woofers told me that as I'm not looking for incredibly high output levels (100-110db is ok) I could easily use the other one he suggested. A 15hz F3 @100db . ... buuuut I'm more than happy to wait a few months for the better suited Ultimax. (EDIT: I think I also found a shop that has them still in store!)

What little do you know about passive radiators? What I read, and what those guys told me, is that it would allow a lot lower F3 because it is ported in a way. Pros against ported is that there is a lot less port noise. Cons: it is more expensive (240 euro to be precise).

Last edited by Droogne; 10-23-2017 at 03:09 PM.
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post #21 of 22 Old 10-23-2017, 04:46 PM
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Quote:
Originally Posted by Droogne View Post
The guys who would sell me the Dayton woofers told me that as I'm not looking for incredibly high output levels (100-110db is ok) I could easily use the other one he suggested. A 15hz F3 @100db . ... buuuut I'm more than happy to wait a few months for the better suited Ultimax. (EDIT: I think I also found a shop that has them still in store!)

What little do you know about passive radiators? What I read, and what those guys told me, is that it would allow a lot lower F3 because it is ported in a way. Pros against ported is that there is a lot less port noise. Cons: it is more expensive (240 euro to be precise).
The main reason I do not think the PR is good here is the RSS460 driver doesn't have enough Xmax for higher output(you need to move a lot of air) like the UM18 can give you at 10-15hz and below. Even to hit 100dB at 10hz is no small feat and the RSS460 is not the driver that would be my first choice when for a little more money I could get the UM18 that has more Xmax and has around 3dB more output down low.

@SBuger has both sealed and ported so he can tell you how they compare for NF use. As far as I know, he is not using his ported 18" or 15" NF he uses his sealed for his NF subs. Maybe he has another reason for not using the ported NF.

And it depends on what you want. If you are ok with just getting "feel" from the NF subs into the teens that ok. I like the fact I can feel the sealed NF into the single digits. Like I mention I have a Crowson and I haven't used it in months because the sealed 18" NF gives me enough that I don't really miss the Crowson. It is nice to have the Crowson because it does add to the experience but a sealed sub NF can be really impressive all by itself. Granted there is not a lot of content at 10hz or below but it is nice to be able to feel it if it is there.
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Last edited by bscool; 10-23-2017 at 04:54 PM.
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post #22 of 22 Old 10-25-2017, 05:07 PM
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Quote:
Originally Posted by bscool View Post
The main reason I do not think the PR is good here is the RSS460 driver doesn't have enough Xmax for higher output(you need to move a lot of air) like the UM18 can give you at 10-15hz and below. Even to hit 100dB at 10hz is no small feat and the RSS460 is not the driver that would be my first choice when for a little more money I could get the UM18 that has more Xmax and has around 3dB more output down low.

@SBuger has both sealed and ported so he can tell you how they compare for NF use. As far as I know, he is not using his ported 18" or 15" NF he uses his sealed for his NF subs. Maybe he has another reason for not using the ported NF.

And it depends on what you want. If you are ok with just getting "feel" from the NF subs into the teens that ok. I like the fact I can feel the sealed NF into the single digits. Like I mention I have a Crowson and I haven't used it in months because the sealed 18" NF gives me enough that I don't really miss the Crowson. It is nice to have the Crowson because it does add to the experience but a sealed sub NF can be really impressive all by itself. Granted there is not a lot of content at 10hz or below but it is nice to be able to feel it if it is there.
@Droogne , yep both ported or sealed work very well for Near Field. The key with sealed though IME, is that you get the driver about as close as you can to the back of your chair (VNF - Very Near Field) to get the most out of it. Ported works great this way as well, but will have a little more TR around tune than the sealed. With a ported sub, you can get away with it just a little bit further away than the sealed (at least around tune), but still needs to be really close to get the maximum effect for impact and TR.

I've used both ported and sealed VNF. I now use sealed 18's right behind my seat(s) and ported up front FF (Far Field). I do also use a small ported MBM tuned to around 50hz as well stacked on top of the sealed 18" right behind the MLP to help with mid bass chest slam.

I primarily went with sealed so I could really feel it all the way down into the single digits and not have giant sized ported boxes to get the tune that low. Sealed subs work great for this if they are positioned VNF with driver facing into you, and as close as you can get it. Like bscool, I'm a huge fan of it.
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