Subwoofer Decision

 Vandersteens method of having a capacitor in line to roll off the low frequencies was also done very early in the Dahlquist DLP1 crossover.
In it you could change capacitors/resistors to suit your impedance and roll off frequency. Not sure if anyone else implemented a similar approach.
If you are at all handy with a soldering iron you could pop the top on your amp and install a pair of caps inline on the RCA + inputs. This would roll off your amp at a chosen frequency. Say 80Hz or so. Then your powered subs fed from your pre can  go down from there using their built in crossover. The crossover calculations are available online to determine the size of caps and (resistors) needed.
Vandersteen rolls off the entire frequency band, (via MIT caps in the pair I had) sends it to the subs and then has a boost circuit in the subs power amps to regain what was taken away, while the main speakers are then passively being fed (with roll off intact) thru the subs connections.
Works fine, just a different way.
Nowadays digital processing seems to be the preffered method via devices such as MiniDSP.

I think that bdp24 for has raised points that seal the deal for the Rythmik 12G  over Vandersteen 2wg as to the bass response and appropriate for jazz and fusion jazz (some R&B and little classical) which I listen to mostly. I am a bass player, both contrabass and electric bass (5 string mostly) and I need to hear those low frequencies well and strong. The frequency of low E is aprox 31 Hz and low C on contrabass with C extension (used mostly by classical bass players) is aprox. 33 Hz and low B on 5 string and 6 string basses aprox. 31 Hz, and low A on piano is 27.5 Hz. I need to hear these clearly and with authority therefore 2 Rythmik 12G-SEs should work well for me. This model has the paper cone driver. Looking for dealer in southern California Los Angeles county. Do these ever show up on Audiogon? I need to hear these but almost willing to buy on what I know now from responses here. I am investing in RTA and calibrated mic to help with placement. I now have authority to move sub to space for my basses and keyboard behind listening area in living room and in dining alcove a living room connected area making L shape to living room an extra 80 sq ft to living room. Really looking forward to new subs.

Sorry low E is aprox 41 Hz not 31 Hz as mistake in previous post

It seems like a lot of fuss over what is pretty simple if your room is relatively controllable (if you don't live in an empty shipping container or a large desert tent)…I use 2 older REL subs (Q150e and Q108II) and no DSP, and they are extremely easy to tune to the room…just move them around and tweak the levels (the 108 is downward firing and right behind my left main in a corner created by a gas fireplace, and the more powerful 150 front firing is near the right wall and can be moved around easily…unobstructed and pointed at the sweet spot). Simply use the level settings and "crossover" (my mains only go to 58hz, so that's my starting point to tweak them) pots carefully and you're in there…these RELs cost around 200 bucks each used, and are utterly great things. Also, I think "lowfreqguy" initially simply misstated the 31HZ E thing as he later mentions the "low B" on a bass which IS 31hz…I say restore his points and declare the penalty voided.

Have you considered the Swarm? Multiple subs, single connection, rave reviews. Worth a look or listen...