As far as I understand it, could be wrong, but with a dipole speaker the sound is produced in phase in one direction and out of phase in the other. This creates a null in sound, so if you are standing right beside it then you can't that a speaker is right there, like a direct radiating speaker. These are what is used to surround speakers. They fire in phase towards the tv, and out of phase away from the tv, which produces a bigger sound field. A bipole is just a speaker which fires in phase in 2 directions. Hope this helps
i think it has to do with how where you place the surround speakers in relation to the listening position. having the speakers directly to the left and right of the listening position as opposed to behind the listening position requires different speaker setups. i forget which is which though. sorry i cant be of much more help.