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Discussion Starter · #1 ·
Righteous Dudes (and Dudettes?),


First off, thanks to everyone who participates in this forum. I've learned a great deal in my few months of browsing AVS. Secondly, sorry for the redundant topic, but I can't seem to find the answer I'm looking for.


I am working on a system for mostly movies and TV. The room that its going in is quite large 18'x37'x10' (6,660 cu.ft.), and it is open to even more space. But the listening area is 18'x18'. The TV is directly above a fireplace. I spent last weekend cutting the mantle in half so I don't have to stare at the ceiling to see the TV. The floor plan can be seen here:
http://www.dsldhomes.com/CmImageDir/182__1372269911.pdf


I was initially going with dual sealed 12" or 15" subs on each side of the fireplace because of WAF. Also to help with room modes. BUT, I'm hearing that sealed subs are not the way to go in large rooms because of the loss of room gain in the lower end.


Are there any guidelines on this topic? A few people have suggested that you really need to go ported if your room is over 5000+ cu. ft. Is +/-3db down to 19Hz on a sealed sub the same as +/-3db down to 19Hz on a ported sub? Would a sealed 15" sub play as low as a ported 12" sub in a large room? The only home theater subs I have experience with have been ported.


What I really need is for someone to tell me that going with sealed subs would be a bad idea or not. Or, that I would have to spend a significant amount of money to get the same low end output as a ported sub from a sealed sub. I don't need earth shaking bass, but I do want it to sound "full" or "significant." I look forward to your comments.
 

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Discussion Starter · #3 ·

I'm not really locked down on a price. I'm pretty good at delayed gratification, so if I'm not comfortable with the amount of a purchase I can hold off until I save enough money. I find wanting and/or researching an item is almost as much fun as having it.

 

With that said, I was initially leaning toward two SVS SB-2000 at $700 (or SB12-NSD at $600 while they last). I am willing to pay $1000 for each sub; $1200 max.

 

To save some cash, I am also willing to buy a driver and plate amp kit (eg. Rythmic DS1200 or DS1500) and build my own cabinet using a proven design. I've built a few ported and sealed boxes for car audio and I am familiar with Thiel-Small parameters and cabinet tuning. Actually, that may be more fun.

 

These subs will likely have to be right up against the wall so back-ported designs are a deal-breaker. I will likely be limited by the depth of the cabinet. Hence, wanting to go with sealed subs.

 

Thanks for your help!
 
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From what I know, you won't be getting much room gain with sealed subs in that size room.  So I would suggest ported with as much output as you can get.  Your best option within your budget imo would be dual HSU VTF-15H, which should come in under $2k.  After that, it would be the Rythmik FV15HP, which offer a substantial increase in output, but will run close to 1400 each shipped.  The only other option would be dual SVS PB or PC12 Plus.

 

Since you are open to DIY, I think you could get much more bang for your buck going that route.  But premade, I don't think you will do much better than the above options.
 

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The room volume and listening space don't matter; the longest room dimension does. Where that's 1/2 wavelength (565 divided by the dimension in feet) is where cabin gain begins. Ideally you want the sub f3 no higher than that frequency, which is difficult to achieve with sealed below 40Hz. You can use sealed without cabin gain, but to get the same results you'll need at least twice as many of them, which eliminates their size advantage, and greatly increases system cost.
 
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Quote:
Originally Posted by bear123  /t/1520026/large-room-ported-sub-rule-or-rule-of-thumb#post_24414563


Your best option within your budget imo would be dual HSU VTF-15H, which should come in under $2k.  After that, it would be the Rythmik FV15HP, which offer a substantial increase in output, but will run close to 1400 each shipped.  The only other option would be dual SVS PB or PC12 Plus.

+1


That about sums it up. Your room is far too large for acoustic suspension subs, unless you get about 4 of them. A pair of the HSU or Rythmik would be your best bet, unless you went DIY.
 

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Discussion Starter · #7 ·

Quote:
Originally Posted by bear123  /t/1520026/large-room-ported-sub-rule-or-rule-of-thumb#post_24414563


From what I know, you won't be getting much room gain with sealed subs in that size room.  So I would suggest ported with as much output as you can get.  Your best option within your budget imo would be dual HSU VTF-15H, which should come in under $2k.  After that, it would be the Rythmik FV15HP, which offer a substantial increase in output, but will run close to 1400 each shipped.  The only other option would be dual SVS PB or PC12 Plus.


Since you are open to DIY, I think you could get much more bang for your buck going that route.  But premade, I don't think you will do much better than the above options.

Bear123, thanks for your advice. I think the depth of the VTF-15H will prevent me from using it, but if I go DIY its great to have reference sub to aim for.


I know in my original post is asked that someone just tell me if sealed subs would work, but I was hoping to keep this from being a "recommend-a-sub" thread. I would really like to get a discussion of the parameters involved in sizing a sub for a room and how the room affects the output of sealed and ported enclosures.


For example, It sounds like Bill Fitzmaurice is saying that all that matters is your longest room dimension and f3 of your sub. I am going to assume that he is implying (hypothetically) that a sealed and ported sub with the same response curve would sound virtually identical in a given room. Its just that finding sealed subs that play as low as ported subs are hard to come by.
 

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I think it would be safer to say that sealed subs generally extend lower than ported.  Ported tend to have higher output around their port tune regardless of room gain.  Sealed subs require either good room gain, more power, more subs, or a combination of the three to match ported subs around their port tune, but will have higher output below ported subs tune, as a ported sub drops off very sharply below tune.  A sealed sub has a shallow drop off below 30-40Hz.  My advice, stop in at the DIY forum and mention your max budget and room dimensions and see what the DIY guys come up with.

 

If you are DIY capable, you will get a lot more output with your budget than buying premade subs.  Check out data-bass.com, they have quite a few DIY subs tested.  This might help steer you in the right direction as well.
 

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Discussion Starter · #9 ·

Quote:
Originally Posted by Bill Fitzmaurice  /t/1520026/large-room-ported-sub-rule-or-rule-of-thumb#post_24414881


The room volume and listening space don't matter; the longest room dimension does. Where that's 1/2 wavelength (565 divided by the dimension in feet) is where cabin gain begins. Ideally you want the sub f3 no higher than that frequency, which is difficult to achieve with sealed below 40Hz. You can use sealed without cabin gain, but to get the same results you'll need at least twice as many of them, which eliminates their size advantage, and greatly increases system cost.
 



Bill, my longest uninterrupted room dimension is 37-ft. Using the equation you posted (565 ft/s / 37 ft) equals 15.3/s or 15.3Hz. Using SVS's products as an example, the SB-2000 and PB-2000 both seem to have a "baseline" response of 100dB. The SB-2000 appears to have an f3 around 21Hz. The PB-2000 appears to have an f3 around 16.5Hz along with ~3dB boost between 20-30 Hz. Is this, in a nutshell, what you are saying? That the f3 of sealed subs is usually too high for large rooms and that's why they don't respond as well?


Rythmik claims that their F15HP is 3db down at 14Hz. The chart they have published is very "low-res." Does this mean that this sub would work well in my scenario? I think with 600 watts (X2) the baseline output level would be sufficient.
 

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A safe assumption is if you want output below 18-20 Hz, sealed subs can get you there. More ported subs will just get you more output from the tunning frequency and higher. Sealed subs can be used in larger rooms with good results. They need to be corner loaded, placed nearfield and have eq to boost the low end safely. I use sealed subs in a large room, 53-5600 cu ft. I have good extension to around 10-12 Hz.
 

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Quote:
Originally Posted by jchata2  /t/1520026/large-room-ported-sub-rule-or-rule-of-thumb#post_24416747


I am going to assume that he is implying (hypothetically) that a sealed and ported sub with the same response curve would sound virtually identical in a given room.
True.
Quote:
Its just that finding sealed subs that play as low as ported subs are hard to come by.
Also true. If sealed did go as low with as much sensitivity and displacement limited output as ported then there would be no such thing as ported, as they'd serve no purpose. But they don't.
Quote:
Using SVS's products as an example, the SB-2000 and PB-2000 both seem to have a "baseline" response of 100dB.
That's at whatever power they measured them at, which they don't say. It's not 4 watt/2 meter, that's for sure.
Quote:
The SB-2000 appears to have an f3 around 21Hz. The PB-2000 appears to have an f3 around 16.5Hz along with ~3dB boost between 20-30 Hz. Is this, in a nutshell, what you are saying? That the f3 of sealed subs is usually too high for large rooms and that's why they don't respond as well?
According to the SPL charts at SVS the SB2000 f3 is 25Hz, the PB 2000 17Hz, so unless the longest room dimension is 22 feet or less I'd go with the PB 2000 if you want the best possible result to 16Hz, though not by a huge margin according to the charts. BUT...that's assuming both were measured with the same power level. They might not have. In order for a driver to go lower in a sealed cab the driver specs result in lower sensitivity than a driver optimized for a ported cab. That's where specs can be misleading, because it you don't know all of the fine details then you can't make a valid comparison. If the PB 2000 was measured with significantly less power input than the SB 2000 that would give the PB even more of an advantage. Not knowing the driver specs I can't be sure that they were measured at different power levels, but I'm highly skeptical.
 

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Quote:
Originally Posted by jchata2  /t/1520026/large-room-ported-sub-rule-or-rule-of-thumb#post_24417435

Quote:
Originally Posted by Bill Fitzmaurice  /t/1520026/large-room-ported-sub-rule-or-rule-of-thumb#post_24414881


The room volume and listening space don't matter; the longest room dimension does. Where that's 1/2 wavelength (565 divided by the dimension in feet) is where cabin gain begins. Ideally you want the sub f3 no higher than that frequency, which is difficult to achieve with sealed below 40Hz. You can use sealed without cabin gain, but to get the same results you'll need at least twice as many of them, which eliminates their size advantage, and greatly increases system cost.
 



Bill, my longest uninterrupted room dimension is 37-ft. Using the equation you posted (565 ft/s / 37 ft) equals 15.3/s or 15.3Hz. Using SVS's products as an example, the SB-2000 and PB-2000 both seem to have a "baseline" response of 100dB. The SB-2000 appears to have an f3 around 21Hz. The PB-2000 appears to have an f3 around 16.5Hz along with ~3dB boost between 20-30 Hz. Is this, in a nutshell, what you are saying? That the f3 of sealed subs is usually too high for large rooms and that's why they don't respond as well?


Rythmik claims that their F15HP is 3db down at 14Hz. The chart they have published is very "low-res." Does this mean that this sub would work well in my scenario? I think with 600 watts (X2) the baseline output level would be sufficient.

Go to data-bass.com and look at the output difference between the PB-12 and SB-12NSD. The PB-12 has a 6-10db advantage between 16-20hz. Your room will not allow enough room gain to make the difference up. Go Ported!
 

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Discussion Starter · #14 ·

Quote:
Originally Posted by basshead81  /t/1520026/large-room-ported-sub-rule-or-rule-of-thumb#post_24417606


If the HSU VTF-15 is too big then look at the PSA XV-15's...they will get close to the performance of a VTF-15 but on a smaller foot print.
 



The PSA XV-15 is out because it is rear ported. Right now everything is leaning toward a DIY ported box because of depth dimension restrictions.
 

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Quote:
Originally Posted by jchata2  /t/1520026/large-room-ported-sub-rule-or-rule-of-thumb#post_24420736

Quote:
Originally Posted by basshead81  /t/1520026/large-room-ported-sub-rule-or-rule-of-thumb#post_24417606


If the HSU VTF-15 is too big then look at the PSA XV-15's...they will get close to the performance of a VTF-15 but on a smaller foot print.
 



The PSA XV-15 is out because it is rear ported. Right now everything is leaning toward a DIY ported box because of depth dimension restrictions.

That is a great option...I would look at the SI D2 18" or Dayton Ultimax 18", Marty Cube flat pack enclosure, Inuke 3000 DSP amp.
 

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Discussion Starter · #16 ·

Quote:
Originally Posted by derrickdj1  /t/1520026/large-room-ported-sub-rule-or-rule-of-thumb#post_24417442


A safe assumption is if you want output below 18-20 Hz, sealed subs can get you there. More ported subs will just get you more output from the tunning frequency and higher. Sealed subs can be used in larger rooms with good results. They need to be corner loaded, placed nearfield and have eq to boost the low end safely. I use sealed subs in a large room, 53-5600 cu ft. I have good extension to around 10-12 Hz.
 



Derrick, one of the subs could be corner loaded, but I was hoping to stay symmetrical around the display for WAF. Near-field is not an option for me. Audessey SubEQ HT will be handling the EQ'ing of the subs, but I don't know how low it EQ's to.


I am curious as to what your sealed set-ups in large rooms were.


I was starting to lean heavily toward dual Rythmic F15HP's (or a replica DIY build with their driver and amp kit). They claim it is -3dB at 14 Hz! I contacted Rythmik about it, and they said I would likely not be happy with them for home theater use. They recommended building a replica of their FV15.


As an aside, Rythmik's Direct Servo technology seems pretty cool, and enables a given driver and enclosure to operate outside the response boundaries you would normally expect. Is there anything equivalent to it in the generic DIY market?
 

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Quote:
Originally Posted by jchata2  /t/1520026/large-room-ported-sub-rule-or-rule-of-thumb#post_24421689


I was hoping to stay symmetrical around the display for WAF. ?
That almost guarantees a less than good result. Subs need to go where they sound the best, which is almost never where they look the best,
Quote:
As an aside, Rythmik's Direct Servo technology seems pretty cool, and enables a given driver and enclosure to operate outside the response boundaries you would normally expect.
But not outside what the laws of physics will allow. As we say in the speaker designing business, there's no such thing as a free lunch. Any gain in one factor will always be offset by a loss in another. For instance, using EQ to lift the low end with a sealed sub. Yes, it works. But each 6dB of EQ boost gobbles up twice the driver excursion and four times the amplifier power. That's fine if you've got plenty of excursion and power to spare, not so much if you don't.
 

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Quote:
Originally Posted by jchata2  /t/1520026/large-room-ported-sub-rule-or-rule-of-thumb#post_24421689

Quote:
Originally Posted by derrickdj1  /t/1520026/large-room-ported-sub-rule-or-rule-of-thumb#post_24417442


A safe assumption is if you want output below 18-20 Hz, sealed subs can get you there. More ported subs will just get you more output from the tunning frequency and higher. Sealed subs can be used in larger rooms with good results. They need to be corner loaded, placed nearfield and have eq to boost the low end safely. I use sealed subs in a large room, 53-5600 cu ft. I have good extension to around 10-12 Hz.
 



Derrick, one of the subs could be corner loaded, but I was hoping to stay symmetrical around the display for WAF. Near-field is not an option for me. Audessey SubEQ HT will be handling the EQ'ing of the subs, but I don't know how low it EQ's to.


I am curious as to what your sealed set-ups in large rooms were.


I was starting to lean heavily toward dual Rythmic F15HP's (or a replica DIY build with their driver and amp kit). They claim it is -3dB at 14 Hz! I contacted Rythmik about it, and they said I would likely not be happy with them for home theater use. They recommended building a replica of their FV15.


As an aside, Rythmik's Direct Servo technology seems pretty cool, and enables a given driver and enclosure to operate outside the response boundaries you would normally expect. Is there anything equivalent to it in the generic DIY market?

The subs I use are the Chase SS 18.2 and stacked SS 18.1's. So, basically two SS 18.2 subs. They are not going to win the WAF since they are black and plain looking, lol. Rhthmik IMHO makes a great subs and multiple subs will need to be used for a strong low end. Budget is a constraint for most people and is a prime consideration. A happy wife will make to a happy man with his HT.
 

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Discussion Starter · #19 ·
It looks like I'm off to the wonderful world of DIY. Likely a down-firing, front-ported box. I saw that Bill Fitzmaurice (along with others) has some intriguing information about the advantages of down-firing orientations.


Thanks to everyone who replied to my thread!


-James
 
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