Subwoofer insight.

But I guess "coloring" the sound of the sub(s) the same as you are the loudspeakers is a defendable notion.

Nope. Only true if the subs are 100% transparent.

Doubly untrue on tube amps due to transformer/main interaction.

Though Rythmik provides high level inputs (on those plate amps I mentioned above), Brian Ding is in favor of low level sub connections. When I learned of high level, my first thought was "Why add power amp distortion to the signal being sent to the sub?" But I guess "coloring" the sound of the sub(s) the same as you are the loudspeakers is a defendable notion. 

I have REL subs and prefer the low-level connection.

Ignore everything millercarbon says.

Unless you want your system to sound really, really, crazy good.

Why is a subwoofer high level connection genius?
IMO, it's as hopeless as trying to mate a whale with a mackerel.

Rolling the low end in the mains and properly integrating phase and level therewith blows the doors off padding the low end unless one is very, very lucky.

I researched both REL and Rythmic.  I think either one is a good choice, but I think the high level connection designed by REL is genius.  The high level connection allows the subwoofers to play more like woofers.  The key is calibrate then to not play too loud.  If you can detect them you either have the volume turned up too high or you need to calibrate the crossovers to blend seemlessly.

I have a pair of Paradigm Prestige 85F towers.  Originally, I was going to buy a pair of REL T9i"s, but went with a pair of REL S3 SHO's.  Glad I went with the S3's.  No matter what you decide, go with a pair.  Much better sound than just one.  I would not get anything smaller than the REL t9i's.  Right now playing two bookshelf speakers is lacking an enormous amount of bass.  You could also purchase towers unless you have a space limitation.  If you are limited in space and have to settle for bookshelf's, spring for a pair of the REL S2 SHO's.  I can put you in touch with someone who can surprise you with a great price.  This was how I could afford the REL S2's.

As they say, you only know what you know. So far I have been impressed with my results with the RELs.  I suppose I would need to move outside my comfort zone to take the advice what many are saying here.  I do feel like the air is moving.  The only thing that seems bothersome is having to readjust the volume based on what is playing.  Sometimes to boomy.  Seems to be album to album.  Not song to song. Maybe I am doing something wrong but only had them 1 day.  

For Elliotbnewbcombjr, I think what you are saying is to come out of the 4ohm taps that the main speakers are coming out of to the high level input of the RELs.  I could easily do as I have female banana spades on the REL high level cable.  However, REL says best to come out of 8ohm or 16 ohm taps.  Appreciate your insight.  

Roll the low end out of the mains with a simple cap XOver, say 80-100Hz.

Check out  http://www.ielogical.com/Audio/SubTerrBlues.php for integration advice.

I ran a single 10" w TC-50s in 16 * 30 * 7 to good effect.

Adding good low end increases realism beyond all proportion. The operative word is good. As a composer friend opined on hearing my system "Every other subwoofer I've ever heard just boomed!"

Were I you, I'd opt for something with continous phase and a polarity inversion. Without them, integration will be problematic at best and impossible at worst.

Check out 2x ML800x as control is far more extensive than the RELs

Ignore everything millercarbon says.

One of those posts that sounds really technical and plausible... only it just isn’t so. There’s more going on than is dreamt of in your simple techno world, elliott.

In the real world all these extra circuits and wires you need, they all diminish the signal to some extent. Its just a fact. Nobody ever made the perfect component that doesn’t do this and until they do simpler is better.

In the real world the more sources of low bass the better. If you want to get all technical this is one where we can go and the tech and physics are solid as can be. Each woofer creates room bass modes based on its location. The more locations the more modes. The more woofers the less output needed from each one. So the more woofers the smoother the bass. Its been researched and tested and proven. Its science.

Also happens to work in practice. To a lot of us, this means more than any number of high falutin theories. 

So when you filter bass from the stereo pair you aren’t improving you are worsening.

Keeping track, that’s two ways your idea made the system worse. There’s a third.

Money spent on this unnecessary and counterproductive crossover and amp and all is money not spent where it could actually do some good.

About the only time this might be a good idea is in the case of a very low output SET where relieving it of low bass might actually be enough of an improvement to be worth it. Except notice, no one with a SET actually does this. Why? Isn’t this the prime example of when it should be most beneficial?

Except people are drawn to SET and low output in general because they enjoy listening for the truly subtle compelling detail that carries one away with palpable presence. The very same subtle detail all your extra circuits ruins. So the one guys who according to your view really should be advocates want nothing to do with it.

Me neither. https://forum.audiogon.com/users/millercarbon

using different speaker taps directly to mains and directly to subs denies a fundamental advantage of self-powered subs. the need for bass comes from the source, the main amp will still be trying to make/send all bass, the main speakers will still be trying to make all bass.

you want to remove low bass signals going to both the main amp and main speakers, especially inefficient and range limited mains, like yours. then they both can do a better job.

preamp out to crossover, or preamp to sub with adjustable crossover, self powered subs,

then signal less low bass back to main amp or integrated amp line in. main amp now doesn’t need to deal with low bass signals. low bass signals no longer seen by inefficient main speakers, those speakers no longer ’try’ to make low bass.

ideally easy ability to adjust sub’s crossover and adjust subs volume. this has to be done while they are in their intended location, again, bass is not always mono, so I advocate a pair of front firing subs near the mains. if hard to access controls, and heavy, put them on low rolling ..., pull out, adjust, slide back in place, listen.

https://www.harborfreight.com/3-wheel-wood-dolly-68902.html?cid=paid_google|||68902&utm_source=google&utm_medium=cpc&utm_campaign=&utm_content=&gclid=Cj0KCQjwpLfzBRCRARIsAHuj6qWcMDbLR0VXw9jAtn61ag27StU_K4EksISZLszpwDFyat6cqTCiGJsaAsenEALw_wcB

When it comes to two channel music, nothing in my opinion rivals REL subs. For your room size, you need to go with a pair of S5 or newer S/812.

I switched from JL audio to REL Carbon Limited and couldn’t be any happier. You can always send an email to REL support and they will reply with best recommendation based on your main speakers.

support@relsupport.zendesk.com

I had a pair of T7i’s with my Dynaudioo Contour 60’s in a much smaller room. They really expanded the sound stage and the overall sound. Just upgraded to a pair of REL S510’s. Another big jump in SQ and now they really dig deep. I would recommend the 510’s or the 812’s for a room that big. 

I'm a REL S5 SHO owner. You can't go wrong with REL as long as you match correctly to your mains and room size. IMO the T series is a bit smallish for your room size. I think a stereo pair of the 812se is probably more what your room size needs. Call REL directly and they will help you match to the right sub in their lineup. 

GLHF!

In my experience and in my opinion....  

An 8 inch subwoofer in a 28' x 38' x 9' room?   I don't think so.  It's all about moving air. A single 8" driver can't move enough air.   2 x 8" drivers can't move enough air.  8 x 8" drivers can't move enough air.    

I use 2 x 18" subs in a room 14' x 26' x 8 1/2' and have them properly corner-loaded.  And I'm thinking of going to 4 x 18".   They are Eminence Kilomax Pro-18A drivers.  Bullet-proof.  

For your room, I would suggest 4 x 21" drivers and use them below 30hz.  If you want subs to go higher, then consider 8 x 15" (4 per side) using VERY STEEP low-pass filter at 45hz.  32hz / octave is the minimum low-pass slope, the steeper the better.   The object is to keep the anything over 60hz off the sub drivers.  It will cause transient time smear and other problems.  

@cheeg 
You are very welcome. 
Apologies to the OP for digressing from his question but depending on how sophisticated you want to get, an external crossover might be something to consider.

Hi @ghosthouse —
thanks for the specifics, and for the link — very informative!  I was wondering how to limit the low-end signal to my main speakers, and SVS has a good solution. Happy listening!

Hi @cheeg -
The SB1000s offer good flexibility input wise. See the photo at the link here. They can accommodate speaker or line level input. I’m running 2 sets of speaker cable...one pair to the Forests, a second pair to the subs, both from the outputs of the integrated amp. Don’t know why speaker level input doesn’t overload the subs but it doesn’t.

When running a low power amp (e.g., First Watt F7) I can use output from the pre to line level input on the subs and then line level out from the subs into the power amp; only 1 pair of speaker cables from power amp to the Forests in this case. The fixed 80 Hz high pass filter in the subs will limit the low frequency signal the amp has to handle and lessen the load on it. Not an option with the integrated amp as I don’t have a separate pre-out on it.

I’m thinking because speaker level input impedance of the SB1000s is 2000 ohms the amp isn’t stressed.

https://www.svsound.com/products/sb-1000

There are separate right and left 8 ohm taps on the integrated so seems okay for connection purposes.  Main speakers hooked to the 4 ohm taps. Super nice guy I dealt with today.  He gave me a couple of weeks to see if they work for me.  Now I just need to figure out how to get these jokers dialed in properly.  Thank you Eric for the room treatment advice. I recognize that the room size is somewhat of a problem.  I think the best I am going to be able to accomplish is maybe some local treatments around the equipment.  My wife is never going to allow anything hanging on wall.  I don't blame her.  It is as much as her house as mine.  I also appreciate Millercarbon advice on more subs but no way she is going to let cables run across her main living area.  Anyways, I got them hooked up without dialing in or proper positioning.  First impression is good.  Somewhat of guttural feeling or sensation.  Never listened through subs before so it is different indeed.  Need a little more time to get it as right as situation allows, watch some videos, read some discussions, etc on how to do it properly recognizing that there are limitations without professional room treatments and the like.  Any pointers (either personal or recommended videos or articles) from those who have similar experience as I am going though on how to properly dial them in would be appreciated.

@ghosthouse
It sounds like you are using powered subs, but feeding them with a "speaker level signal from the amp" -- doesn't that cause overpowering of the sub?  I would think it also halves the impedance of each channel, which can be a challenge for the power amp.  Do the cables from each sub go directly to a pair (R or L) of power amp outputs, or to a pair of (R or L) speaker terminals? I wouldn't think it makes a difference, but I've learned not to trust my assumptions in this hobby.  

With that large of room, Audio Kinesis Swarm is worth checking out.  Mcarbon used the same Audio Kinesis Dayton amp and built his own swarm from 4 unassembled box speakers from Dayton.  I used car audio sealed sub boxes and Kicker drivers.  Now trying find space for a 4th sub box, my room is much smaller than yours.  As gochurchgo mentioned 6 are even better for a large space.  I have a very good friend that sells car audio, hence my choice, and he insisted on letting me pay cost only.  2 years ago we built a Howe truss bridge across a creek on property he owns ten miles out of town in the woods.  

Make sure your room acoustics are dealt with first. They can make speakers sound larger than they did before, by tightening up the bass and controlling the mid/treble.  Talk to GIK acoustics.

That's first, next, subwoofers are great, but be prepared to take some effort to integrate them well.

If you want to get the highest technologies ,and performance plus a great app for phone or tablet and 2019 sub of the year 
SVS 3000 SB for $995 delivered , 45 day audition 
don’t like it they will even pay the freight back .
i have a $1600 JL Audio,and rel sub that we’re both over 1500
this SVS sealer sub is so much more advanced
and even borrows from the flagship all technologies and is a 13 inch Aluminum driver and over 25 lb driver 50 or 52 bit processor 
the 2 part pole piece uses the small inner section for low volume,and outer as demand requests it ,meaning very tunefull
tight Bass even st low volume ,unheard of and only a 14 x16  52 lbs , and the app all adjustments and volume from your listening position , if you want to tune the room ,buy the $90 Mike and rew
on your computer , and truly tunes your room ,a learn8ng curve there though, and SVS can assist on that. Thunderous Bass to 
earthquake 18 HZ. One is plenty ,but for movies and just to balance the room two is best . Highly recommended !!

What are the original speakers?  The specs seem fine, but it's hard to relate otherwise....*S*

6 subs or don’t bother.

ricmci, if you wonder if more subs really is better, check this out. https://systems.audiogon.com/systems/8367My first sub was the Talon Roc in the corner. A fine sub. But only one. One does not work very well. (Sorry, guys, but it doesn't. Can't.) Once I learned about the distributed bass array and decided to build my own the original play was to get the DBA up and then sell the Roc. Because who needs 5 subs?

So I built the 4 and removed the Roc and the DBA was awesome and was just about ready to sell the Roc when for kicks decided to try and see what it would be like with 5. Well it didn't add bass, its not about more, its about better, and 5 is a lot better. So the Roc stays. 

That's what you want. Don't worry too much about which ones. Four of just about anything will be better than one of anything. Four really good ones will be even better of course but mostly its about numbers not quality. Don't worry about placement. Placement with one is a huge headache, and nothing works anyway. Placement with two or three gets easier, because with more subs there are more modes and its easier to have them smooth out. Placement with four or five is trivially easy. Pretty much anywhere you plop them down you will hear awesome bass. 

I worry that by awesome you think I mean better than usual. No. I mean awesome. The exact word that was used three times by the last guy to come and listen. Deep, articulate, powerful, smooth, and 3D in an enveloping immersive way you have to hear to believe.

So get your two. For now. Consider it a good start.

FWIW - I’m running a pair of SVS SB1000 subs alongside Totem Forests (2 ways and similar sensitivity as your speakers). The subs are receiving a speaker level signal from the amp. Both subs and Forests run "full range" via parallel runs of speaker cable. The subs are dialed back such that you only know they are in use due to the blue LED lights or if they are switched off. Definitely, bass is improved but what shocked me was the improvement to midrange clarity and "openness" running the subs brought. I can’t explain why this is so but this was further enhanced when I upgraded power cords running to the subs. Given the Forests by themselves go a little deeper than what you cite for your speakers and given the audible benefit (not just better bass) I’m hearing from the SB1000s, I’d encourage you to try a pair of subs. (I’m assuming the RELs you are considering are self-powered). Hope this is helpful.

Adding a Rel sub to a pair of Kef LS50s was one of my better decisions. The sub filled in the bottom end and increased the soundstage (depth, in particular). The little Kefs no longer sounded small. Would like to add another sub but room layout is very limiting.  

Darn good idea.

Your existing speakers may sound great, however they are bass limited, and inefficient as you know.

1. a stereo pair of self powered subs is a very good idea, don't over do it. two, located near the mains, so the low bass and the overtones from those notes are directional.

2. removing the need for your existing amp to handle the bass is going to allow it to do a better job with your inefficient mains.

3. easy independent volume control/balance with the mains is nice, if buying new, remote vol of sub would be very nice. 

Two is a good start. Much better than one. Or none. One thing you will learn, if you're smart enough to try, is the more the better. One sub is better than none and sometimes kinda sorta matches. Two is better still. With four you find all of a sudden not only is the bass smoother faster deeper and more articulate, but it also blends seamlessly in a way that makes all the speakers disappear along with the room as you are enveloped in the sound field. 

So yeah, go for it. Great place to start.

I find most any subwoofer/s is better than none. 
Its thrilling when you realize how much low frequency information you've been missing. Similarly, when you discover the further improvements as a result of the proper room placement and calibration of the two subs or more.
Your in the mob now.

BTW, no responses from Kenjit allowed. Ha!