Subwoofers for Magnepan 20.1s?


I used Granite Audio's Ultimate Low Bass CD and my 20.1s go to 25Hz at -10dB and my room is 16x26x10 (speakers approx 6ft from back wall and 3.5ft from side walls on ends). I can get -6dB in the 29-33dB range and then it is pretty flat with a slight drop in the 50-60Hz range. I am not a bass fanatic, but on some recordings, I wish I had some further lower bass extension without becoming unnatural sounding/boomy. I know HP likes Nola Thunderbolt subs with the 20.1s. Has anyone tried them or any others? Other system components: Pass X250.5 amp and Xono phonostage, Audio Research Ref 3 preamp and Ref 8 CD player, VPI superscoutmaster reference turntable/10.5 tonearm, Dynavector XV1S cart.
powerdoctor
Dukes Swarm is a good design. Martin Logan Descents work well,but you will need at least 2. Also KSC has a 31.5in driver in custom bass system which was designed with large loudspeakers like maggies in mind. Low excursion bass systems have far better transient responce over large excurtion floor corner reinforced subwoofer systems with all there many comprimises in design. The large driver only moves slightly so less detail is lost than hi-excurtion designs. Lots of detail in low bass most never experance this since they use conventional sub designs.
John--several of us noticed that you used the (slightly) less expensive version of the 31.5" driver in your bass cabinet and were wondering what your thinking was in making that decision? The more expensive one appears to have a free standing resonance frequency, doesn't it?
Yes, I agree go sealed with low group delay and large woofer. It will be expensive as a good tight sub means less SPL output - so you need really big rather than a high output resonant sub
One word of caution re: subs w/extra large large drivers.

Just be sure they can be crossed HIGH enough in frequency to suit your needs. I know that people generally like to cross as low as possible, but if you eventually decide that you want to EQ problems in 50hz to 60hz region, you'll be crossing at 75, 80, or 90hz. I don't know the 31.5" driver in question, but I'd imagine that it's not designed for optimal performance that high up, since some manufacturers of 15" drivers caution potential buyers about this issue.

Just food for thought.

Marty