Which subwoofer should I get?

I have 2 one for each channel, MK-70B’s dual 8" drivers (push/pull) that are super fast. You can go up the ladder for the larger cones, & resale would be no problem if they don’t match. YMMV

I’m also limited for space & could have got a set of 125s to match my Klipsch Lascala bins, but the location wouldn’t let them breath, so I stepped down the ladder a few notches.

I heard my first ’high end" loudspeakers in 1971. One was the Infinity Servo-Static, the other the ESS Transtatic. Both had woofers that reproduced pretty low bass, the Infinity by virtue of a single servo-feedback 18" woofer, the ESS a KEF B139 woofer in a transmission-line enclosure. The Infinity retailed for $2000/pr (a lot of money in 1971), the ESS $1200/pr. Being an itinerant musician, I could buy neither.

Then in 1982 I saw a pair of the Transtatics for sale locally, for $400. One B139 had been replaced with a knock-off, but a call to ESS and the speaker was restored good as new. I still have 'em. Back in ’73 I had heard the original Magneplanar loudspeaker, the Tympani T-I. It was love at first sight, and I bought a pair. I was stunned by the quality of the bass produced by the two woofer panels of the Tympani, which reproduced the sound of my Gretsch 26" bass drum (recorded in my living room with a pair of small capsule omni condenser mics plugged into a Revox A77) better than any other speaker I had heard.

I provide all the above info to establish my love of clean, lean, "un-fat" reproduction of the low frequency sounds produced by percussive instruments, in particular. Bass drum, piano, and acoustic and electric bass, first and foremost. I have made music with a lot of electric bassists, and with three players of upright acoustics. The sound of an acoustic bass is very unique, it’s character being like the low register of an all-string orchestra. Like the low register of a piano, but more "sinewy".

Harry Pearson chose the Tympani bass panels as the woofers in his custom Frankenstein loudspeaker creation, feeling they reproduced bass unmatched by normal dynamic woofers. Having lived with Tympani’s on-and-off for over 50 years, I completely understand his opinion. Tympani bass is free of the "plumpness" most woofers add to the sound of an acoustic bass.

When Danny Richie of GR Research approached Brian Ding of Rythmik Audio, it was with the intention of combining Danny’s talents at designing OB loudspeakers (including woofers) with Brian’s excellent servo-feedback woofer system. The resulting product is the GR Research/Rythmik Audio OB/Dipole Servo-Feedback Woofer, the only one of it’s kind in the world.

I say all this because I find the OB Woofer to sound more like Tympani Bass than any other woofer using dynamic drivers than I’ve heard. Brian Ding himself finds the OB Woofer to sound too lean, but I (and Danny Richie, and other OB Woofer owners) disagree. I think all other woofers sound too fat. I base that on my experience playing a drumset right next to an acoustic bass, as well as hearing lots and lots of bass drums and pianos in recording studios. You would be amazed at how much electronic manipulation recording engineers add to the raw signal coming into the monitor booth.

But the OB/Dipole Sub is not for everyone, or every system. For those people and systems, the regular Rythmik Audio subs will do just fine.

My personal choice would be the REL subs, I'm also a believer in using two subs, one for right channel and the other for left channel.

Thank you one and all. It seems like a “tie” between the REL and Rhythmik subs. I have heard of Rhythmik, but never heard them. One of the things I’m concerned about is having the properly sized sub for my room, which is 19’x17’x9’ (peaked roof design). My listening position is centered on the 19’ side of my room. I too expect to get two subs, but will start with one (for a variety of reasons). Finally, due to pricing, I am planning to buy REL used, but Rhythmik or SVS new. 

REL is the OPPO of the HiFi world, over-hyped because magazines like The Absolute Sound said it was great but many cheaper alternatives do better.

I'll vote for SVS if you want to save a few bucks and like the app.

I'll also throw in the Paradigm XR13 which adds room correction, sound fantastic with music and has a better aesthetic value (comes in a few finishes if that's important)