Seeking advice on Speakers that create an intimate 2 channel listening experience

Duke, the "reason" I was referring to is your facts about the SPL drop difference between point source subs (yes, they are omni-directional, but for this discussion that is immaterial) and line source loudspeakers. Dipole planars share the 3dB drop off per doubled distance figure with line sources; a "6dB" sealed or ported sub will then be balanced with a planar speaker at only one listening distance---halve or double that distance and there will then be a 3dB imbalance. A dipole sub, on the other hand, will remain balanced with a dipole loudspeaker at all listening distances (assuming of course they were balanced to begin with ;-).

Finnish company Gradient offered dipole subs for both Quad ESL’s, the 57 and the 63. They were compromised by poor drivers and electronics, unlike the OB/Dipole Sub from Rythmik Audio/GR Research. Rythmik’s Brian Ding designed the sub’s plate amp/control panel and dipole-compensation network, and has the electronics manufactured for him in China. Danny Richie designed the OB-specific 12" woofer, and has it made for him by TC Sounds, well known for their superior woofers (including the monster 18" LMS 3400).

In addition, sealed and ported subs load the room differently than do planar woofers (such as the two bass panels in the Magneplanar Tympani T-IVa loudspeakers, a pair of which I own) and open baffle/dipole woofers and subs. The dipole null to either side of planars/line sources/dipole subs eliminates sidewall-to-sidewall modes, and with both the front and rear of the woofer cone/planar Mylar being "open" to the room and therefore not increasing and decreasing the bass pressure in the room itself---as do sealed and ported subs (when the cone moves inward, room pressure is decreased, when it moves outward pressure is increased)---the sound of the room itself being pressurized is conspicuously absent. Employing four subs instead of two does not provide that benefit, does it?

The OB/Dipole Sub offered by GR Research in collaboration with Rythmik Audio is more Danny Richie’s (GRR) baby than Brian Ding’s (Rythmik). Danny is a proponent of open baffle loudspeakers and subs, and when he learned of fellow-Texan Ding’s new servo-feedback subs thought combining Brian’s servo with an open baffle woofer would set a new standard in low frequency reproduction. And so it has! Ding prefers the room-loading characteristics of sealed and ported subs to that of open baffle/dipole. Each to his own. ;-)