I punched in "bipolar speakers" into the search function here and got this, hope it proves useful:
"Should I use bipolar, dipolar, or tripolar surround speakers?
Surround speaker placement, room acoustics, and personal preference are as important as the speakers' radiating characteristic. These factors vary greatly, so Dolby Laboratories cannot recommend a particular speaker for home theater use.
Bipolar, dipolar, and tripolar surround speakers use speaker drivers aimed towards the front and back of the room to achieve a diffuse soundfield like that created by the multiple surround speakers used in movie theaters. Your room's acoustics will effect these designs more than conventional direct-radiating speakers, which, when placed properly, can also make effective surround speakers."
Punching "dipolar speakers" into the search function yielded this tasty tidbit:
"Our Recommendations
We start with one of the several well thought out THX speaker placement guidelines (note we agree these are simple guidelines and not a biblical source). The goal is great localization for the front soundstage, tight articulate bass in all seats, and a surround array for movies and music with some sense of directionality for games. The surround array should envelope more than localize though with some of our recommended addendums to the THX configuration you can have the best of both worlds with a simple automated configuration change, and/or some trick post processing modes incorporated in many of today's receivers.
In this recommendation, you can use identical performing LCR speakers, with Dipole/Bipole or Direct radiators for the Surround channels and Direct radiators for the Surround Back channels with the listener located about 2/3 into the room from the front speakers and digital delay compensation implemented on all speakers to properly time align the speakers."
Not touched upon is the essential difference between bipole and dipole speakers: the former has its drivers in phase with each other giving a diffuse yet more localized source, the latter has its drivers out of phase with each other and by nature diffuse less localized, and perhaps not as precise.
