Subwoofer Decisions - REL/Rythmik, Pair/Single, Paper/Aluminum Driver, etc.

I have decided to upgrade my subwoofers. I have a 15x12 room with an open side wall that I use for 2 channel and HT. Two channel music performance is the priority. We don’t listen to either very loud or need the room to shake. I am considering the REL S/510 and the Rythmik F12, F12G, FM8, L22 and E22. I have an all Linn vintage system. My speakers are Aktiv by installing special crossover cards in the 5 channel Class V amp. It outputs to the speakers in a bi-wire configuration. If I used a high level speaker connection I guess I would have to tie into the speaker wires connected to the Bass/Mid card.

Any thoughts on Rythmik v REL? You seem to get a lot more for your money with Rythmik and they also offer more options - finish, sizes, configurations, etc. Supporting a Texas based business is also nice. Do they offer equal or better quality and performance? There seem to be many fans that think so.

Any thoughts on Rythmik’s paper v aluminum drivers? The owner says that the aluminum driver retains its shape faster and is more detailed. He recommended the aluminum in my system over the paper even for 2 channel. The paper is lighter and has better extension above 80Hz. I’ve also heard that it is better at low volumes because it easier to move. My current subs have paper drivers and paper seems to be greatly preferred in the audiophile community.

Any thoughts on pair v single sub in my size room? One 10 or 12 is probably enough to pressurize the room but will a pair of dual 8 or 12’s make everything easier and better? Is there a point where they will overwhelm the room?

Things are pretty tight in my room so the smaller footprint of the vertically stacked FM8 and L22/E22 are appealing. Also stacked drivers look badass right? The FM8 with its dual 8 inch drivers will probably be faster than the larger 10 and 12 models. It also appears to go plenty low enough to keep up for basic HT needs. The L22/E22 have a smaller footprint than the single driver F12 but I’m concerned that those might be overkill.

High level speaker connection? REL recommends it. Rythmik offers it but recommends using other methods. Anyone know if using it with a Class V amp and tying it only to the bass/mid speaker output will perform well? I’m not sure how REL implements its filters to make this work. Is the high level connection really better in performance?

Thanks for the help.
“Two channel music performance is the priority”.

A pair of REL’s s/510 would provide seamless integration through high level connectivity and superlative bass for 2 ch & HT.

Brace yourself...subwoofer discussions here ends with no consensus!
The a crossover with high pass is the most important part. With a good crossover you can greatly improve your sound. With just a low pass you are just extending the bass (which is fine too...but not as good). Two subs will be much better. One sub can work fine for a single seat but it is much harder to get right. I would take two cheaper subs over one pricy sub every time. 
I can’t comment on the subs you are looking at. I have never really demoed subs back to back but l like sealed high powered subs for music. 
Interestingly I have found that all most all the speakers I have tried crossover best right around 60hz. Something about 60hz seems to optimize both the sub and speakers. Maybe not forcing the sub to play too high or the mains to play too low. Not sure but this has been with multiple speakers and rooms. Anyway give 60hz with a high pass a try.  
Also keep in mind that speakers will cancel out the bass 1/4th the wavelength to the rear wall. If you put your speakers 4ft off the wall there will most likely be a hull at 50-55hz. You can place the sub less than 36” (from the driver face) from the wall to avoid this cancellation. Another options is bring everything more than 6’ off the wall to avoid bass cancelation but this is not practical for most.  
Here is a chart that can help. It will be quicker to calculate it for a starting point. Between 3’ and 6’ the bass with have major issues but this is where speakers should go for soundstage and midrange tone. But placing the subs (less and 36”)  and speakers in different spots can fix it.

This video might help too. Not exactly related but will make more sense than my rambling lol.
The most important thing with subs is to have a lot of them in different locations. Four small ones distributed around the room is way better than any one or two no matter what or where or how powerful. This is a lot easier to say than to understand so if you are serious then do a search and read up, you will find nothing but screaming praise from those of us who have actually done it all saying the same thing. Also those who have not (and therefore do not know) are not shy in spreading what they do not know. So you kind of have to read past that. Try.

If you can really only have floor space for one, or two, then Tekton 4-10 is the way to go. Get two.

And just to be clear this is not to have two times or four times as much bass. The reason, which you will find clearly explained all over the place if you look, is every sub no matter what or where you put it generates peaks and nulls. Using more subs in different locations creates more peaks and nulls in more places. But having four lets you run each one at a lower level. The result is they all sum together into much smoother, deeper and more powerful bass than you can get any other way.

There's no such thing as "overkill", but at the same time, your goal shouldn't be to "pressurize" the room (unless you're listening to Bassnectar at 11), but to seamlessly blend them with your speakers so that they don't call attention to themselves.  You want them to deliver all the bass that's there in the music, the lower frequencies that most speakers can't deliver, but not overpower the midrange and treble. 

I think you get a lot of bang for your buck with Rythmik and I like their servo technology, but also like SVS and Power Sound Audio.  Get as much and as many subs as you can afford.  Spreading out the load and using multiple subs to cancel out peaks and nulls is a good thing.  My room is a little bigger than yours and opens into a kitchen/dining room area.  I have two Rythmik F25s and two SVS SB13 Ultras (both are sealed subs).  Not overkill.  

In my system I am currently using a REL S5 SHO, a Rythmik F12SE and two SVS SB4000’s. My room is 10 x 14. When I first started using the REL, I used the speaker level input but have since changed to using the rca inputs. To me using the line level inputs there was slightly less distortion giving me a slightly cleaner sound. The Rythmik has the best sound of all three though it has a little less output power. The SVS has the most output power of the three, but the sound quality is not quite as good as the Rythmik but a little better that the REL. The sound quality differences between the three are noticeable but not substantial. If you are not using some type of external crossover the Rythmik and SVS also give you more tools to help with integration.

If multiple subs overwhelm a room that is just an integration error and can be easily fixed. The intent of multiple subs is not to create more bass, it is to balance out the bass through out the room. It is a type of acoustical treatment for the room as explained by MC and Big Greg. 

Why a pair of "Rythmik E22" instead of a single F12? I ask because this is my dilemma. The F12 has an AB amp while the E22 has the Class D amp. And I was thinking for musicality I would prefer the F12SE...

But sight unseen and no listening tests make any purchase a leap of faith. I was also interested in the REL S/812, but for all their (paid) reviews, I have heard more than a few personal horror stories about them not integrating properly.

Still would love to sit down with the REL s/812 and both the Rythmik E22 and F12SE and put them to an A/B/C listening comparison test. (price is less consequential as I have already placed money aside)
About 6 months ago I got 2 Rythmik F18's (sealed subs) for my living room setup.  Musically, they are flawless. 

After some HT experience with the F18's now, one can contrast the signature of more "standard" (or somewhat sloppy) bass that is the norm in HT/movie theaters vs the super controlled bass from these.

I can see why some people get used to the other way, but I'm liking the sense of control.  It can be a lot of fun, if a bit eerie how bass can be so suddenly there or gone.
I have a pair of REL S/812. Took me about a month to dial them in but they are good enough that I’m thinking of building up a stack. However, I worry about the difficulty in dialing in 2 more subs. My room is asymmetric so my settings for each sub is a little different. 
Hmm, just noted the earlier thoughts about the L22/E22.  When I bought my pair of F18's, I had started by considering a set of 2 L22's (the E22 was not available at the time and they didn't mention it to me) since it fit my physical constraints for WAF, but since I was going for audiophile results they told me the L22's weren't a great choice and I eventually ended up with the F18's.  If the E22's had been available I'd almost certainly have bought those, so would be curious how they work out for you.
Shortly after I bought the E22’s the REL T9x’s came out. Since both REL and Rythmik offer generous trial periods I decided to buy both so I could be sure I made the right decision and had no doubts about my decision. I hooked both up in similar ways - LFE + high level with the REL’s and LFE + Line in (from line out in each mono amp) with the E22’s. The E22’s have more options to get them perfectly blended with my speakers and my room. In addition to the typical crossover and volume settings there are EQ options to address room modes, damping options, variable phase control, high pass filters, and more. Using UMIK and REW, I was able to see exactly how all of these options impacted the frequency response in my room. The E22’s being sealed with direct servo technology were tighter and faster than the REL with its passive radiator. They also seem to be a much better value too. The E22's are slightly less than the T9x and offer similar specs to the much more expensive 212/sx. In the end, I definitely preferred the E22’s and happily kept them over the REL's.
@snatex I made exactly this decision recently and went with F12SE Rythmiks for the reasons you mentioned -- ability to dial them in to a pretty tricky room. I got a pair. Trying them out. Have an older REL which I love, too, but didn’t want to buy a new matching pair. I will do measurements, soon, and really appreciate the ability to adjust a number of various factors on the Rythmik. I did a little listening last night without doing much more than playing with some dials and they sounded great. I put my REL at a distance and ran it, too. I think something nice is happening with all 3 subs and I may not sell the REL after all.

There is so much to love about both companies and products that there's really no shade to throw toward either. Both are excellent options and since I use REW/Umik, too, I wanted a subwoofer with variability I could both hear and measure. 
It's refreshing seeing other members using REW/Umik to see exactly what's going on in their environment. I have Rythmik E15HP2 subs.

I just don't understand how some guys just plunk their subs in any location, use bass heavy music, and adjust the volume according to a hand full of songs - except when a heavier bass song gets played, they adjust the volume again. Seems like a waste of money to me.

As an example, without using measurements, they have no idea if there's a bass hump, and by turning down the volume on the sub to address an issue like that, they lose out on the other bass frequencies because they've just made them inaudible. Forget about trying to achieve a flat bass response without using measurements - the advantage is you get to hear all bass frequencies.

When I was trying to choose between REL and Rythmik, I considered cost, size and weight, and place of assembly. Those factors led me to choose a pair of Rythmik F8s. I have not regretted that choice at all and appreciate the array of options to adjust output to the conditions in the listening room and the application (two-channel music or multichannel home theater). If you do go with Rythmics, my only suggestion is to use the switch to power them on manually rather than using the feature that powers them on automatically when they receive a signal. I did have some issues with the auto power on setting. 
Very helpful discussion for me.  Have been considering MJ Acoustics or REL (have owned both), but am very much circling in on a pair of F12SEs (or possibly FM8s).
Quick update -- the Rythmiks work beautifully, and the extra controls on them were very helpful for adjusting them to the room. I have kept the REL also, and it’s now adding something to the mix as a third sub, further away in the room. Adjustable phase is really valuable, and this was proved beyond a doubt both in measurements and in how it all blends in listening. There is no peak or dip greater than 6 db and mostly much less. My room has 6.5 ft. ceilings, so this is a major accomplishment for me.

P.S. Ascend Acoustics, the Rythmik dealer I used, were great to deal with.
I am frustrated by the quality control of Rythmiks speakers AND also their  customer support. I received a Rhythmic 12 sub a year ago and the power connector was damaged and did not work!!!!! After a couple of back and forths with the company (where they claimed it was a faulty power cord) it was not the power cord it was the IEC socket. I just gave up. The sub works as long as I do not move the sub 1 inch either way. I dont know what to do BECAUSE I have tried to contact the company numersous times and all I get is a delayed e mail....power cord on the way.
I have no purpose in dissing the company in fact I was led to believe by the Cable Company that Rhythmik was superior to Rel (most of the time).
I have no suggestions at this time...but I am not going to bite the bullet and pay for me sending the sub back!!!!!
With MC and others, I have to recommend going with as many small decent subs as you can instead of one expensive sub. Minimum: try for two good 10” or 12” models. The distributed bass array concept works, and very well; it’s science. I just moved out a great REL B1 and moved in three SVS units (two SB-2000s, one SB-3000) and the bass and openness is better; I’m not going back. I’d like a fourth.

And, there are a lot of very good high-performance inexpensive subwoofers out in the market today like Rhythmik, HSU, SVS, plus the higher priced RELs J&Ls, etc. I’d consider 2-4 of good $600-?00 subs, seriously.

Unless you have amplifier concerns I’d not worry about high-passing unless your mains need that high pass. For higher volume playback it might be beneficial to keep energy away from main woofers possibly. My mains run unimpeded and all subs are low passed at 50Hz (with low volume). The increased ‘air’ is wonderful.

Sorry if that wasn’t what you wanted. After fiddling for 40 years with sub ‘specs’ and technical BS I now realize the DBA concept totally runs that old thinking out of town (at least in my own practical experience, and like that of many others).

Golfnutz, I forgot to respond to your excellent comments on plopping and ‘hearing’ one’s way to good bass.

As regards plopping, based on the DBA concept one merely needs good asymmetrical positioning around the room. Of course more adjusting could be done, ad infinitum I suspect. Sometimes you do your best and call it a day. I’m already happier without going wild on positioning, yet…

And my ears did not adjust the bass levels. I wanted the flattest, lowest bass possible with no humps or exaggerations so I ran lots of frequency sweeps down to 20Hz in 1/3 octaves and dialed it all in without my ear. That gave me a pretty flat bass down past 31Hz.

The true ‘proof is in the pudding’ moment was when I played the first track (Signe) off of Eric Clapton’s “Unplugged” album with the three sub-woofers dialed in. For the first time I noticed the air pumping or chuffing coming from something on-stage just past the two minute mark. I was amazed as it was so soft and so low in tone I barely picked it up. Now I know it is there. An ‘ah hah’ moment.

Thanks for the response musicaddict.

I have nothing against DBA, it’s just how some guys install multiple subs in their room with absolutely no thought, then make comments on Audiogon about how amazing everything sounds, including better mids and highs. So many OMG moments, but without any proof that what they’re hearing could actually be better - way better. At least measurements are a way to back the claims up. Basically, it’s better because I said it was (I just turned the volume so you could barely hear the bass) - OK, good for you then. Except, they’ll adjust the volume down on the subs again when a heavier bass song comes along. Again, no idea what bass frequencies they’ve just removed from anything they should be hearing just because they have a peak somewhere and don’t know it.
Also, what if someone could actually get a very good looking frequency response curve from say 150Hz down to 20Hz with a couple of subs. Let’s assume within plus/minus 7dB across that frequency range. Is it really worth the cost of adding 1 or even 2 more subs just because someone says the more the better ? And what if adding more subs actually makes the curve look worse, or only corrects it to within 5dB?
We have the tools to help with evaluating what’s going on, there’s no guessing or throwing darts at anything. Yes, it might take some extra work to go through many test scenarios, but at least we’re informed along the way - no false claims.

BTW - none of my comments are directed at you, or anyone else in particular.

Yes TB!
I've owned subs from Rel- the Stadium III and S/3, Rythmik F12G and SVS SB3000. I had the Rythmik and SVS together and think the Rythmik is the better but couldn't identify one over the other consistently in a blind test. The nice feature with he SVS is being able to control all the settings with an app. It allows me to play around with the volume and frequency during certain songs or movies. Adds a fun factor, one of the reasons I enjoy audio. The grill on the SVS is a horror show, looks like Darth Vaders helmet. 

I have three subs in a room with a ceiling that is 6'5" high. It's a very difficult room. What allowed me to manage the bass with the Rythmik's adjustable phase. The left Rythmik is set at 270; the right Rythmik is set at 30. The REL is further away and set at 0. I could never accomplish what I did without the adjustable phase. Take a look at my system, the first picture and see what it's made possible.
That’s a good example hilde45 of being within 7db from 100Hz down to 20Hz. So my question is, would the cost justify the purchase of another sub to flatten out that 5db peak? That’s assuming it could be flattened.
It would be interesting to see the phase and group delay on your screen shot. I only say this because of how you’ve set the variable phase on the Rythmik subs.
Thanks, golfnutz. Actually, it's within 5 db. In a room where I had very very awful problems!

It wouldn't be worth buying another sub, yet — from what I read, if one is within 5 db they should count their coins and leave the betting table.

I will try to amend the photo with some details, but they're really only relevant to my room.

Also: I will move to another room within a year, I think, so it's not clear yet what that room will require.