Few people have heard either the Linkwitz Lab or GR Research open baffle loudspeakers, both of which include open baffle woofers. Linkwitz uses a pair of 10" woofers in an M/W frame, GR Research a choice of two or three 12" woofers in an H frame, with a dipole cancellation compensation circuit incorporated into the Rythmik Audio plate amp that comes with the DIY kit, along with Rythmik’s servo-feedback system. Bass response to 20Hz.
The GGR/Rythmik OB/Dipole Sub was developed in a collaboration between Danny Richie of GR Research and Brian Ding of Rythmik Audio. Danny was already offering OB subs in kit form, when he learned of Brian's new servo-feedback system. He thought combining OB woofer design with servo-feedback might produce state-of-the art bass reproduction, so proposed the two of them join forces.
Danny is a longtime die-hard OB enthusiast, more so than Brian. Brian himself finds the sound characteristic of the OB/Dipole Sub "leaner" than he cares for, preferring the extra weight of sealed and ported subs (of which he offers in a vast array of models). If you've heard the low frequency reproduction produced by the big Magnepan models (the old Tympani line, and the current 30.7), you have an idea of what the GRR/Rythmik OB/Dipole Sub sounds like.