@clio09, Though the OB/Dipole Sub uses the Rythmik A370 plate amp/Servo-Feedback woofer system and is sold by Brian Ding on the Rythmik website, the design is more Danny Richie's (of GR Research) baby than Brian's. Danny was already making an OB/Dipole when he heard about Brian's new Servo-Feedback design, and contacted him, thinking the combination of OB and S-F would produce a new standard in bass reproduction. Owners of the sub agree!
Brian Ding, though appreciating it's abilities, finds the OB/Dipole a little too lean sounding, without the weight and room-pressurizing he likes to hear in a sub. All the enthusiasm for the sub originates with Danny, and the best discussion about it appears on the GR Research AudioCircle Forum rather than the Rythmik AVS one.