Dipole and bipole refer to speakers that have drivers on opposite baffles. To put it crudely, they squirt sound out of both ends. Our feeling is that this type of sound radiation isn’t desirable for front channel speakers. You get a spacious soundstage but at the sacrifice of image specificity. Soloists sound as big as the room. Pavorotti may be a large guy but he’s not 10' wide. Orchestras may be large but you should be able to precisely locate individual instruments within the group. If not done properly, dipolar or bipolar speakers may also exhibit frequency response problems due to phase cancelations (particularly true with narrow baffle designs). Polk front channel speakers use wide dispersion drivers to provide open, spacious sound staging while maintaining pinpoint localisation.
But the lack of image specificity of dipolar or bipolar speakers is just the ticket for rear channel use, especially in Dolby Pro Logic systems in which the surround channel is mono.

In a dipolar speaker, the two sets of speakers are out of phase with each other; while the drivers on one side are pushing, the opposite side is pulling. The result is that there is a null or a dead zone of sound in the area along the 90 degree axis of the speaker. Why is that good? When properly set up, a pair of dipole speakers used as surround speakers will provide a very open, enveloping rear effects soundstage without allowing you to pinpoint the location of the speakers themselves. That’s a good thing. But for all this to work properly, the speakers need to be positioned in-line with the listening position as shown on the illustration. If you are sitting out of the null area, the effect is ruined. What if you can’t or don’t want to place your surround speakers and listening position as required? That’s where bi-poles come in handy.

In a bipolar speaker, the two sets of drivers are in phase with one another - both sides push air at the same time. The result is greater sound output where the dipolar speaker’s null would be. Theoretically, a bipolar speaker approaches a 360° sound field - it disperses the sound all around the room. That’s a good thing if you need to position your surround speakers behind your listening position or anywhere outside of the null area. Some people prefer the greater localisation of bipolar speakers when used in digital discrete (Dolby Digital 5.1, DTS) systems.

Polk F/X speakers give you the choice of either polar pattern so you can choose the one that sounds best to you in your setup.