Ahhh--Problem solved. Adding a REL sub-bass unit...

I'm wondering how many audiophiles have given up on loudspeakers preamturely, or have gone down the rabbit hole of cable swapping to "fix" an issue with their speakers.  

I grew up hating subwoofers and home theatre.  I still haven't come around fully to home theatre.  I've warmed up though.  I've had my own issues with otherwise great loudspeakers, including a pair of Klipsch Forte IIIs.  I was very frustrated as I'm feeding them from a respected tube integrated, I've tried them with a 300B amp, and I've toiled over positioning.  

The issue that I was having was the mids and highs were dominating in my room--despite the size of the woofer and passive radiator. Some recordings were just too bright.  Sometimes I felt the speaker, however "alive" and dynamic was not imaging well, needed soundstage help, and so on.  

I hate to say the REL T9i I threw in the mix today is a panacea because there's always stuff to tweak.  Yet I have experienced this before with a Sumiko subwoofer.  Adding one to the mix and dialing it in so that it's barely audible has brought everything into focus.  Everything is more relaxed and energetic at the same time.  

I'd say that the REL is a room tuning device above all.  I have a larger room (I think it's 15 wide, 24 long and 10 high--in feet).   I'm not sure how much I'd have to spend or what different choices would solve this otherwise.  From a guy that used to reject subwoofers out of hand (my bias came from the 90s home theatre craze) I think that they might be necessary in the lion's share of systems with the lion's share of speakers.  To say, "you don't need a sub" with speakers might be true depending on your room, but I also think in most situations you are missing out on what they can do for so many criteria that are not necessarily in keeping with adding bass--e.g. soundstage, focus, imagine, fullness, taming treble, etc.). 

Finally, I really wish that I could try some other brands as many audiogon members recommended so many respectable names.  I ultimately went with REL because of its philosophy, my similar experience with a Sumiko sub (within the family of REL or somehow related), and the high frequency input connections. 
you’re not alone in your opinion. Paul McGowan from PS Audio fame feels no speaker system is complete without a sub actually recommends using two. He also likes the REL subs. I’m sure many would argue otherwise but he and others make a pretty good argument for using a sub to augment even floor standers. As of late, I’ve been contemplating trying one in my system. Don’t want to spend an arm and leg so may try a less expensive in-home trial with those companies that provide that service.
Ahh you are correct and Paul McGowan recommends using the subs high level inputs ( speakers wires in and out) of the sub so it takes on the same characteristics as your other speakers and provides a more seamless sound.
It only gets  better with...2 REL subs. I agree with those who say ANY speaker system can benefit with properly dialed in subs.
I agree.  And two is better than one.  REL makes great subs.  The high level connection is, in most cases, the way to go.

I just posted in another forum about how I dialed in one sub (T5i) for my system/room.  Essentially, put the sub in your listening position, put on some bass heavy music, then move around the room (you may have to crawl to get your ears at the right level) until you find a spot where the bass sounds good.  Then put your sub there, and go back to your listening position and see (hear) how it sounds.  This will work for your listening position, but if you want the whole room to sound good you will likely need two to cancel out the low frequency resonance peaks and pressurize the room more evenly).

DSP and acoustic room treatments are also good options, but can get expensive and a bit tedious to dial in (plus room treatments may not fit in with your decor, etc.).  And if you are playing vinyl (and why wouldn't you with a 300B and Klipsch speakers), would you really want to digitize your analog signal (it would probably sound great, but it kind of goes against the "gestalt" of your old-school tube and horn system)?

I'm not so sure if adding subs will yield better imaging or "focus" or tame treble at all, but it will certainly add deeper bass and more "fullness" to the sound.  A cheap experiment would be to try out a Schiit Loki ($150.00).  If you don't like it, send it back for a small re-stocking fee.  You'll probably keep it.
Another superior musical sub that provides high-level hookup are the Rythmiks containing the PEQ-series plate amp. The XLR-series amps do not, they are line-level only. Most Rythmik models are available with either plate amp.
Subs definitely have their place and I am reluctantly becoming agreeable that two are needed - some room arrangements more than others.
I disagree that "no system" is complete without a subwoofer. Some systems are so rich that adding a sub is just too much.
JL audio makes some very good subwoofers that have the required specs and features for optimum integration.  
There is still a prejudice against subwoofers in certain audiophile quarters, and there always has been. Subwoofers are often seen as something best left in Home Cinema circles.

For decades we have been told that there are often serious, insurmountable integration issues, with both existing speakers and the room.

Then it’s been argued that since low bass is less directional you only need one subwoofer. That needs to be proved as it sounds a bit like a fudge.

Finally there’s always the option of buying bigger speakers which can offer decent <50Hz performance.

However, a rethink might be needed if we consider the benefits of removing strain off the main speakers and the amplifier by considered the use of a sub. It’s definitely an area that demands more attention.

It would be great to hear of more experiences, good or bad. I know that my PC speakers would sound insipid without their sub.
I have Legacy Audio Focus 20/20 speakers (3 12" drivers) and ran those for quite a while without a subwoofer, using my subwoofers only for home theater thinking I didn't "need" a sub. 

I decided to try adding my two SVS SB13 Ultras to the system and am glad I did.  What they add more than anything is a sense of realism, the tactile feeling you get from the bass coursing through your body when you hear live music.  I could be perfectly happy with the bass from my speakers alone, but adding the subs into the mix elevated my enjoyment level. 
I have Maggies (3.6) for speakers and they need a lot of current, provided, and also a sub to really sing.

I tried them without a sub, but the system bloomed when one was added.  

Just one guy’s experience.
Same experience. I started with 1 REL Strata III and migrated to two REL 218 subs for my system which uses a high efficiency single driver and 300Bs. I highly recommend trying dual REL sub woofers in stereo setup. If you like what 1 REL sub does, you will definitely appreciate two in stereo mode.
For decades we have been told that there are often serious, insurmountable integration issues, with both existing speakers and the room.
Agreed! Currently, there still are those who spread the fear of trying subs. Yes, they can be a challenge to integrate. It certainly isn’t set & forget. It takes a lot of tweaking to get it right. But, it’s more than worth it. Not only can subs solve a ’brightness’ issue, they offer what the recording is supposed to sound like.
Don't know how many speaker systems i 'd have gone through by now ...if i  hadn't acquired a REL.
I was driving a pair of Dynaudio Excite x32 speakers with a Rega Elicit-R. I listen to mostly '70's rock and reggae vinyl. Sounded very good but somehow lacking. I added a pair of REL T5/i's. The RELs, once adjusted properly,  added a certain "weight" to my system, while correcting for my non-optimal listening environment. I am quite happy with them. 
I was using a pair of original Rogers LS3/5a with a Hafler SS or Marantz 8B tubes. There was no real bass without a sub. REL T2 was a gorgeous addition at a reasonable investment. I'm now using Adam Audio powered studio monitors (I always enjoy hearing what engineers hear) and though they have good bass down to 30-40 hz and sound great alone, the REL still fills out the deepest notes. REL recommends corner placement and I've always moved mine back there after experimenting. The polarity switch comes in handy for a final check of where the waves are interacting relative to your seat. And the variable crossover and volume provide endless tweaking opportunities.;-)
(I always enjoy hearing what engineers hear)
Almost no one ever will. The room and electronics are vastly different. Nowadays, by the time the label gets done ’improving’, any similarity between what was mixed and what’s on the disk is quite small. Doubly so for ’remasters’ See http://ielogical.com/Audio/#ReIssues

A system without the bottom octave is a pale simulacrum and loses more that ½ the immediacy of a live performance.

IMO, most systems with subs are egregiously awful. It’s often not the fault of the sub, but the set up:
1. 0-180° Phase controls are only valid at one frequency. If the phase is not correct, the system is likely better w/o the sub. Filters change the phase response making the two controls interactive. Given that small subs have large EQ curves built into their amplifiers, the phase pot marking is next to worthless in terms of absolute phase. 180° phase switches are next useless except when used in concert with a 0-180° phase control.
2. A system with powered sub should use a XOver to remove the lowest frequencies from the mains and is preferrable ot trying to ’blend’. Doing so reduces main power requirements, driver excursion and distortion. Feeding the sub first and then the sub feeding the mains is bollox. A simple single capacitor will give a 6db/octave filter which will give a nice blend with a 18db/octave sub rolloff, provided the sub phase is inverted. Getting the phase and frequency correct is tedious. It can be calculated if one knows the amp EQ, driver response, crossover type and slope. Having a close starting point is vastly preferrable to most of the ’instructions’
3. Many systems crossover an octave too low. IMO, speakers should be crossover an octave above where they start to fail badly. In the case of small monitors like LS3/5a, Spica TC-50, that’s around 100Hz. The problem is then to find a sub with similar sonic characteristics to the mains. If the mains are capable of true 30Hz, IMO there is almost no need and even less probablity that adding subs will improve the system unless the mains are placed for WAF rather than sonics.
4. Ported subs? Never!

When properly set up, pop bass is focused and does not stroll. Tympani and bass drum become focused. The sense that one is there is out all proportion to the measured delta.
See http://ielogical.com/Audio/SubTerrBlues.php for a bit of a primer on integrating a small sub and small monitors.
Yes, I'm getting close to adding a center channel speaker to my setup, but will not do so without, at the same time, also adding a REL sub with the Speakon connection. 

Years back, I tried 3 or 4 center channel speakers, but when using them, I lost all the mid and deep bass presence in the center channel, compared to when I was using my front mains as a "phantom" center channel.  I tried all sorts of crossover settings in both my sub and AVR, but could not replicate the sound of deep male voice that I got out of my front L/R speakers.  So, I stuck with using the "phantom" mode.

Last year, however, I heard a home theater setup in which they were using the REL Ti series subs to extend the frequency response of some B&W 804D3 front channel speakers.  Man, it really makes a dramatic difference to get authoritative and quality bass down to 30 Hz from the front channels. 
2. A system with powered sub should use a XOver to remove the lowest frequencies from the mains and is preferrable ot trying to ’blend’.

If the mains are capable of true 30Hz, IMO there is almost no need and even less probablity that adding subs will improve the system unless the mains are placed for WAF rather than sonics.

4. Ported subs? Never!
Disinformation abounds here.
Thanks for all the interesting details, ieales. 
Disinformation abounds here.
Prefer it if you can refute engineering facts. 

2. - Loudspeaker designers spend great effort creating crossovers for LF/Mid/HF bands. Mathematically it's almost impossible to mate a 12" driver to 8" or smaller driver in a vastly different box with no filter and get seamless integration. The level may be relatively flat, but the phase will be a nightmare. Until one has heard a minimum phase error system playing all 10 octaves, one has never heard bass correctly reproduced.

4. - Ported speakers have large amounts of time / phase shift, and the lower you go, the worse it gets.: "Bass reflex cabinets have relatively poor transient response, causing "smearing" or a longer resonance of the bass notes. Though the sound coming out of the port may have the same phase of that from the front surface, but it can never be at the same time, thus, the extended bass energy is really noise disguised as signal. The disguise works only when the sound is a continuous tone (one of the reason why some people prefer some particular kind of music for their audio system), but reveals itself most apparently at reproducing percussion sound."  https://en.wikipedia.org/wiki/Bass_reflex#Limitations 

As a great musician friend once said on hearing my system "Those little speakers aren't putting out all that gorgeous bass?!?!?!?!?" Informed of the sub, he stated "Every other subwoofer I've ever heard just boomed!!"

@ieales  Knock yourself out.   You're still wrong.    Best to insert IMO in every one of your posts.

You know it really depends on your main speakers whether or not they would benefit from a subwoofer.  As big as my main horn speakers are, they never have produced just enough bass to satisfy me even with more powerful amps,. So a subwoofer was added with excellent results. You want a sub that sounds tight and tuneful (very musical) that creates a seamless presentation.
Now in my other room I have huge but heavy custom made cabinets with 15 inch woofers, they are sealed enclosures, they are capable producing thunderous depth & bass when called upon. I would never need to add a sub to such a set-up.
Very interesting comments to my OP.

I have to say that in my system (with two different sets of speakers and 3 different amps--tube, class D and class G), the system always sounds better using REL/Sumiko’s recommended way of sending the signal from the speaker terminals on the amps to the High Frequency Input on the REL or Sumiko. I’ve tried 2 other ways and the most musical was HFI and not using a crossover on the main speakers--i.e. running the mains full range.

My sub voyage started with a used REL Q150e that was the best 200 bucks (Ebay) I've ever spent on audio...all it needed was new grill cloth, done. Year or so later I found a REL Q108MKII also for about 200 bucks, in perfect shape, needed nothing. Made cables from Canare Star Quad, Neutrik Speakons...done. Easily adjustable, properly placed magic. No DSP needed, small se amp drives the 99db mains. Full range magic.
Yup, a well-integrated sub (or two) can do that. The key word is integration. 

I think many fail at integration because they have their sub(s) crossed over too high and with far too much gain. 
I switched from floor standers to monitors with 2 REL T-7's a few years ago and never looked back. As stated above by a few people, the flexibility of the subs to the source (a recording with low, or high bass) is the best attribute about this set up. Very happy with the sub set up.
Another +vote for REL subwoofer.  Happy Listening!
Some of the best Money I've ever spent was on 2 Sumiko S-10 subs. I had a Rel storm which was not big enough to take care of the 5k cu ft room adequately. It sounded good but the two sibs are much better. I considered other brands but the Rel had given me a sense of what was available with adequate power and size (12'). The Sumiko S-10 are a near equivalent to the Rel S-5 with the same specs. I highly recommend Rel.
I am a SET amp guy and, after testing many speaker and amp combinations, I firmly feel that for my setups a great stand mount monitor paired with good subs is the best way to get great sound.  Properly placed and tuned, a single driver system with subwoofer beats the pants off any full range speaker I have tested.  Again, this is using low output SET amps or SE Pentodes between .7W - 12W output.

When you think about it, subwoofers are really no more than a bi-amp solution in a box.

Disinformation abounds here

You took the words right out of my mouth.  So much opinion spoken as fact in @ieales post.   And most of it wrong.   

Long time lurker here but I thought I would put my two cents in and echo what the OP said. We recently added a REL S-SHO 5 to our two channel system and it just makes everything sound better. In addition to improving the low end, what I had perceived as brightness in the system is now gone. The imaging seems more stable as one moves around the room and interestingly, it sounds better at low volume as well. I think it's more than a placebo effect. I don't understand the physics of why it just sounds so much better overall but couldn't be more pleased. It sounds like a whole new system. For those interested, we have Symphonic Line Legato speakers powered by Odyssey amp and preamp. Large room at 17x35 feet with vaulted ceiling. I'm sure similar results with other subs but REL was recommended by our local dealer who brought one out for an audition.
Not sure that I can contribute much to what has been posted above.  Actve floorstanders have gained a following, and IMO for good reason. I think that spending money on a quality 2 way speaker with a subwoofer or ideally 2 subwoofers is likely to be less expensive and more tunable to the room without DSP.  If I had $15k, the Vandersteen Quatro CT would be at the top of my list. But in my den (12x14x 8’’), a pair of Heresy III and a REL T9i ($3295  total new) with a crossover at 60Hz and a SET is heaven. 
You took the words right out of my mouth. So much opinion spoken as fact in @ieales post. And most of it wrong.
Again, please refute with engineering facts. My focus is on music reproduction, not HT. Ported subs can go lower at the expense of linearity, phase and transient response.

I think many fail at integration because they have their sub(s) crossed over too high and with far too much gain.
Most program has no real bass. By crossing over low, almost no signal is reproduced by the sub.

Again, IMO, not enough attention is paid to phase. 80Hz is 14 feet. 90° phase error is ~3ms. Humans use the time delay between their ears for directional information. Phase error causes instruments to stroll and fatigues the listener.

In a concert hall, tympani, bass drum, bass, etc. are all localizable blindfolded and they do not stroll. In the studio, on phase coherent monitors, kick drum, electric bass, either DI or mic'd, don't stroll either.

Too many HiFi systems have horrendous low end phase which causes the aforementioned instruments to stroll or be impossible to localize on well recorded program. A poorly integrated subwoofer is a headache in waiting.

For more than 4 decades, minimum phase error has been a primary focus. For the same period, listeners always comment lifelike, accurate, precise, etc., regardless of room and hardware.

How many have bothered to calculate the phase response of their XOver, loudspeakers and subwoofer amp to integrate their sub and then measure and analyze the result to tweak and verify?
Without any regard for "bothering" with calculating "phase response of their XOver, loudspeakers and subwoofer amp to integrate their sub and then measure and analyze the result to tweak and verify?," and simply using a test CD to determine how low my main speakers go, I have imaging from my system that is utterly stable and musically accurate, relative to the recording of course (there still appear to be 27 foot wide drummers here and there, but I've learned to accept them). Listeners are fooled into thinking their systems sound great all the time, as shameful as that might seem to some with a more elitist point of view, but I get it.
I’m looking to add a rel to my system.  I’m hoping I can swing the 25.
Look at used RELs on Ebay and Audiogon...if patient you can be rewarded with some amazing bargains.
Indeed this is a most interesting group on sub woofers views.
i am using a pair of old Gallo Nucleus loudspeakers and an old pair of 300-B stereo integrated amplifier.
The equipment is in a 13ft x 12ft room.
i listen to only classical music in particular Bach, Beethoven Chamber Music and Wagner’s operas.
The sound from the system while good, appears to lack some bass and weight.
Since I also have an old REL Strata powered sub woofer I would like to add this in the system.
i am however not too sure on the cross over frequency which best suits the system.
i would be most happy for suggestions and advice on the choice of this crossover frequency.
Thank you guys.
I added a Rel Storm MK 2 to my Quad 2905's. After a little work I have them set up where I only hear more impact.
I can mention that I have had a pair of Rel Storms that I have integrated into my two channel audio  system with floor standing dynamic speakers and planars and can also interchange with some of my stand mount speakers. Very seamless integration, trust your ears.