Bi-amping is the practice of utilizing two audio amplifiers to power a set of loudspeakers (contained within one speaker enclosure).
The speaker system has to be wired to accommodate it as does the receiver, typically with two sets of binding posts, one set for the bass and one set for the mid-highs. A single amplifier can usually power a woofer and a tweeter only through a crossover filter, which protects each driver from signals outside its frequency range. However, the crossovers themselves waste power; bi-amping along with active crossover components works around this problem by putting crossover networks before the amplifiers rather than between amplifiers and loudspeakers.
The result is cleaner sound although some say they can't tell a difference.
An image to help explain.
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