There is a difference between isobaric and push/pull. Isobaric has two woofers face to face and the cones move in the same direction. Push/pull has one woofer facing out and one facing in but the surface of both cones is exposed. Isobaric is used to effectively double up on the specs of a woofer (drive force, mass, etc) and it cuts the needed cabinet size by half. Push/pull is the same as two forward facing woofers but one is turned around and electrically reversed (so the acoustic phase is the same). You can mount the woofers push/pull on an open baffle or H-baffle, a la Linkwitz to achieve cancellation of even order distortion. The link below has good information about push/pull and dipole woofers (look through all the links contained therein):