Subwoofer insight.

BTW, no responses from Kenjit allowed. Ha!

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.

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.

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. 

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.  

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.

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.

6 subs or don’t bother.

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

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 !!

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.

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.  

@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.  

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.

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

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!

@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.

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.  

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!

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. 

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.

[email protected]

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

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

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.

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.  

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.

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.

Ignore everything millercarbon says.

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

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

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. 

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.

Ric, welcome to the world of subwoofers. 
If you notice the woofer booming on certain albums the level is too high. turn it down just a little at a time. There are two parts to this, the sound and the impact. I use two types of music to evaluate subwoofers. A solo acoustic bass (Dave Holland Not for Nothing) and a drum solo (Grateful Dead Infrared Roses.) I use the bass to adjust levels and the drum solo to adjust phase. To start get a tape measure. You want to place your speakers on a radius from the listening position. The two subs should be between the satellites right up against the wall. With front firing woofers I will turn them facing each other so that the side of the driver is right up against the wall. The satellites are just lateral to the subs at the same distance from the listening position again on the arc of a circle. This is a good starting place. Check your levels again. This may take several days of listening to get right. Then play your drum solo and listen (or feel) to the impact of the bass drum. Move the satellites back and forth, towards and away from the listening position until you get the most impact. 
If you are not using a two way crossover (running your satellites full range) keep your crossover low like 60 Hz. Unfortunately this eliminates 1/2 the benefit of using subwoofers. To get the most out of them you need a dedicated two way electronic crossover between your preamp, amplifier and subwoofers. JL Audio makes one. This roll of the satellites, lowers distortion and increases the system's head room (goes louder!) In this case you can take your cross over up higher like 100 -125 Hz. 
Ultimately you would have digital bass management like the Anthem and Trinnov units use. Then you can put the speakers anywhere you want and the system will correct it. 
Always evaluate the sound from your listening position. Bass can change quite dramatically as you move about the room. If you think something sounds off go check it out at the listening position. It may sound fine there. 
Done right the subwoofers should disappear. All your speakers should disappear leaving just music. Doing this analog is not easy. Over the years I have lost plenty of hair on this issue. It took me 30 years to get it just right. 
As a note, multi subwoofer systems like the Audiokinesis Swarm make setting up a subwoofer system in the analog world much easier as they take phase out of the subject so you only have to worry about levels and crossover points. Phase and time are easily the hardest to get right. 

Also, speaker level inputs are only for someone who does not have another preamp output to use. My solution for this problem is to get an electronic crossover. Speaker level inputs are a cost saving way out until you can afford the crossover.

A simple 6db/oct XO HiPass is easy to make.

See http://www.ielogical.com/assets/Audio/PassiveXO1.png for a picture 
The circuit is just a Y with the appropriate cap in the main amp line.

Fc = 1/(2 π R C) where R is Ω and C is in F. 10nF is 0.000,000,010F
R is amp input impedance
See  http://sim.okawa-denshi.jp/en/CRhikeisan.htm

As a general rule for small 2 ways, ½ to an octave above the claimed -3db point is a good rule of thumb. e.g. for 60Hz speaker, 85 to 120Hz. 85Hz is not exactly ½ octave, but close enough.

Use good caps. Teflon or Polypropylene or Polystyrene.
Avoid mylar and worse.

I highly recommend REL and have owned several over the years. Simply visit their website and they have a page where you can enter the data of your room size and speakers and they will match you with the perfect sub. You absolutely will benefit from the addition of the sub in your system.  

Simply visit their website and they have a page where you can enter the data of your room size and speakers and they will match you with the perfect sub

Nonsense!
Limited speaker brands, model choices and room parameters. An utter waste of time!

Some of the most egregious sonic travesties experienced have included REL subs in dealer show rooms.

20 years ago REL were tops and they still make some very good subs today.
Others are price point pathetics.

I started my REL experience a while back with a used (200 bucks) Q150e 10" 150 watt little gem that works perfectly. I'm big on the "high level" Speakon connection as long runs of RCAs is just silly to me...balanced if available would be fine as is the wireless feature on new subs, but otherwise I simply made my REL cables from Canare Star Quad and it works swimmingly. My second used REL came along a couple of years later as a Q108MKII 100 watt 8". Also 200 bucks, also perfect. I'm in the "2 subs or more" crowd as it just makes bass seem more balanced and effortless...however, if one sub is all you can do, do it. Running the main speakers full range also sounds best to me, and since they're very efficient my main amp doesn't need any help with crossovers limiting its bass...I dial in the best sound from the main speakers and then roll in the subs to where they just sound right. Note my room sounds like a room, the room tuning consists of furniture, a rug, and a high sloping ceiling. No deleterious reflections or bass boom issues in my sweet spot. I turn the RELs up and down a little from time to time relative to the recording and very rarely use a Schiit Loki EQ...works for me.

Probably not what you want to hear but I think you should get properly sized stereo speakers for your room. Start there. It sounds like your current speakers are not up to the scale of your room.

Next, find the right location for those speaker and then treat the room. I don’t mean use crazy amounts of acoustical treatment. You can do a lot with very simple choices you make with existing furniture/art placement. One compromise my wife makes is we have no glazed picture frames in the living room. All the art on the wall is sculptural or framed oil paintings...some framed textile art. We have a 9x12 Persian rug and carefully placed furnishings.
It does not look like a listening room and isn’t perfect. But I get slamming bass and holographic soundstage in my listening position. No need for a sub.

I own two subs that are put away. Same issue: constant adjusting of the bass levels. In fact the imaging improved without them. My stereo amp doesn’t need to compete with the powered subwoofer’s transformer.
When you dial the main speakers in...then dial the subs into the mix.
I can’t imagine that a single 10-12” sub wouldn’t suffice for a room of your size. But I tend want subwoofers to just ‘fill in’ what’s missing. Some people like room shaking bass.

See if it is possible to try the subs before you purchase or it you are able to return if you chose to do so. Feeling like you're missing something is likely to be exactly what will keep you in this hobby and chasing that sound forever. I think most of us are always trying to reach another plateau which we think will be better. I think once you get to the point where you feel no further improvement is possible and you stop even exploring the possibility, you have lost what most makes this a hobby- your interest, like adding more horsepower, etc. to you sports car, in making it better. Try the subs and judge for yourself -it's what makes this whole thing fun.

For me it's the extra bass "range" that my subs provide as my main speakers have very balanced bass to their obvious limits (about 58hz)...the subs just make it all more believable. 

The SVS 16s are much better than the RELs for half the money.

rwwear,
"The SVS 16s are much better than the RELs for half the money."
There are no absolutes in Audio, only preferences. I've owned the SVS 15 and SVS 16. I currently own REL Carbon Limited subs. I would never own SVS subs for 2-channel again. 

I have a large room too.  It's not as large as yours, but larger than many.  Anyway, I have a pair of T/9i and Revel F208 mains.  I got a T/9i, but in the large room, it wasn't enough.  So, I changed to one R528 (moved from the HT room).  The R528 was good, but I really felt that 2 subs would be better.  I decided to put the R528 back in the HT, added a second T/9i to the stereo setup, and now I have spent some time with it.

My advice is to use the high level inputs as described in the REL manuals.  I have the mains plugged into the 4 ohm tap on my Primaluna HP Integrated, and the RELs are connected as stereo (see REL setup instructions) using the 8 ohm taps.  This is the way REL recommends, if you read up on their installation instructions from their web site, or in the manual.

Once it was all connected, I spent some time tuning everything.  Then listened.  And tuned some more.  And listened.  After doing this for a few days with a variety of music, I have it dialed in.  At first, I thought it would be better to crossover at a low freq, but then I found that it worked better if I raised the crossover, which is what the manual recommends.  I also found that it was better with the volume levels set higher than I expected.

Overall, the sound has improved for all frequencies.  Everything smoothed out, and the system sounds better than ever.  The subs energize the room, but are not boomy, and they don't overpower the main speakers.

IMO, the T/7i may not have enough power for your room.  But, then again, I don't think you need to jump to major subs, like 18 or 21 inches, as some suggested... unless you want hip-hop bass. 
  

Bottom line, watch the REL videos on how to tune, and follow what's on there web site.  You'll adjust them differently than you expect, and the SQ will definitely satisfy!

The REL's just aren't real subs IMO. They don't even go down to 20hz. I have a friend with a pair of the REL Carbons. Even he acknowledges they don't perform like mine. I personally own Velodyne DD15s and I love them but would go for the SVS 16's if I needed a replacement. But you are right about personal preference Ric.

For 99% of music, you don’t need to go below 20hz. Home theater is a completely different thing.  REL is great for music. 

Listen to My Compensation by Laurie Anderson and you will change your mind.

Good advice to OP. Spend an extra $3k to accommodate one album you don’t have.