Which subwoofer should I get?

I have a few thoughts as a sub user for 20+ years now. I have heard the brands you are discussing and many others. I am firmly in the camp that all systems improve with prosper implementation of subs. 

short answer, will the SVS sound as good as the Rel and cost less?… yep… and a big chance the SVS will sound better as it is tunable.  -6db @ 20HZ Is comical for a sub as the sub still needs room gain to get flat. At which point you are hoping for the perfect amount of room gain. The SVS will allow you to adjust for room gain and a bit of boundary interference.

Rel’s high level input is a joke. No one with a lot of subwoofer experience would choose this connection. Yes it can work fine but why take the time to dial this very old method in. 
 

 In general I would buy the biggest sub you can, think 15” or 18” subs. Each drop in octave takes 4 times the displacement. Your mains have 3x9” drivers with a surface area of 189 square inches per speaker and I bet they have good throw distance too. A 15” subs is 175in/sq and an 18” subs is 254”in/sq.  The less the sub has the work the better it will sound. You have top notch speakers that need top level subs imo.

if you like SVS I would look at the new Ultra 17 ($2500). They have a 30 or 60 day home trial.

If it were my money I would be looking at Rythmic 18 or JTR RS1 with an active crossover. I own the JTRs and have written about them if you want to see my detailed opinion. Big subs that play a wide bandwidth (10hz-200hz) will play 20-80hz with ease. Highpassing the main would take it up another level too. 

@james633 --

+1

It’s telling seeing main speakers with bigger displacement area in their woofer section than the subs that augment them. Indeed, physically subs are quite often smaller than the mains, and knowing Hofmann’s Iron Law we know what it affects (i.e.: sensitivity) - which is not without consequences. Somewhere along the line the dominating narrative has crept in that a physically smaller sub cabinet volume makes it easier to control resonances, effectively setting an upper limit for sub size, but seeing the forest for the trees (and knowing what it’s really about here) it’s also an argument that conveniently supports audiophiles’ resentment towards large sized subs for no other reason really than the inconvenience of size.

Enclosure resonances aren’t trivial, but the question is to which degree compared to lessening the workload of the woofers; smaller/fewer woofers working nearer their limit will effectively negate the work that has gone into making the cabs rigid due to large amounts of mechanical distortion from the driver itself, so it comes down to knowing the difference ease of reproduction (from prodigious air radiation area) a good sub design can have, from cabs that are as rigid as it requires for them not to impede too severely with the overall quality of the bass (hint: it can be done without resorting to builds that weighs in excess of several hundred pounds). For those wondering about the sufficiency of what’s required to make large cabs rigid enough, as an outset at least it only matters that such sub designs produce cleaner, more palpable and effortless bass than their smaller or less efficient brethren.

If one were to abide by the "no resonances"-approach of sub cabs it follows that their weight (and price) would become the actual, practical hindrance way before the woofer size/effective air radiation area would get to a place where it really mattered. Small subs, both with regard to driver and cab size, can be made to sound well with bigger main speakers within morerate SPL’s, no doubt, but that way (unless in multiples, and of course taking for granted good implementation/distribution) one isn’t taking the fuller advantage of what subs can do and how they could complement the overall sound. Shooting for energy linearity into the subs region and seeing what’s required for this to come true is a good starting point, but it’s a rudimentary physical aspect few seem to consider or won’t practically accommodate, so there we are.

my guess would be that, REL subs set ups are such an ease, the use of an APP would be frivolous.

Only Rel subs defied physics and set up with ease in spite of a severely lazy lack of features and integration tools??

"such an ease", Rel marketing is quite funny..

@ James633

This was a VERY helpful post….thank you. The JTR’s are truly above my price point, so will do very serious investigation of the Rhythmik, since you and so many others think so highly of this brand. As suggested by another post, I will contact Rhythmik to get their advice on which subs make the most sense for my room and system. 

FWIW (to all): my local audio dealer is a BIG REL fan and strongly encouraged me to get the Carbon Special. What started all of this was I found a very good used deal on a Carbon Special, and then thought I ought to seek the wisdom of this group……and I’m very glad I did.

Thank you to everyone for your feedback. 

P.S. We’re about to do some construction in my 2-channel room, so will likely wait until that mess is done in a few weeks to pick this back up and make some final decisions.

I would recommend a pair of RSL 12 S subs. I have had many of the subs listed above, and I have to say, the RSLs are "musical", if anyone could know the meaning of what this term says. Very hard to match subwoofers to my Klipsch Lascala dog houses, but I have found them. If you overlook these, you are losing out on a great product at a great price. Many excellent reviews. Happy New Year to all. MrD.