Room size, not so much, but solid walls play an important role. Multi-polar speakers rely a decent amount on the sound being reflected off the wall.
Dipoles work well when mounted either ear height on the side walls or just above the listener, obviously all rooms are different and you have to take into account placement and how affective they will be for each individual situation, for example in a 7.1 setup you could use dipoles for the sides of the seating positions and then direct radiating speakers for the rear channels, this will give good results as the dipoles can fire sounds along the walls and then the direct radiating speakers for rear effects, once again it does depend on the room and placements for them to work well enough and give a convincing rear soundstage...In order to use dipole or bipole how much does the room dimensions, walls etc play a part in their effectiveness? Should this question be on another thread??
It depends as you are used to the sound with the speakers you have, and using something like dipoles or tripoles for that matter you might not like the sound it creates, although I have always had good results with the both sets of speakers, maybe you could speak with a local dealer and they could lend you some to try out?In my case I have a 5.1 set up and due to aethetics I have direct radiating speakers mounted on the back wall elevated and aimed down and toward the listeners. Both speakers are about 18" away from the side walls. I don't know if replacing these rears with bipoles would make a positive improvement or not.onder: