Bipoles and dipoles are generally speakers with drivers on two opposite faces of the speaker box.
A bipole is wired internally such that all cones are moving outward and inward in sync with each other. The effect created here is a wide soundfield that retains qualities of directionality (i.e. you can still localize the source of the sounds).
A dipole is wired internally such that cones on one side are moving outward while cones on the other side are moving inward. The effect created here is a wide soundfield that does not really retain the qualities of directionality. Since the speakers on opposing faces are wired out of phase, the sound waves effectively cancel out when they meet in the middle and the only sound left comes from the periphery. Hence the widely dispersed, non-localized sound.
Then, or course, there are speakers that are hybrids, in which the woofers are wired in phase and the tweeters are wired out of phase.
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