More common in high-quality home systems and pro audio systems, the active crossover splits and filters the signal for each speaker driver BEFORE it enters the amplifiers. This way, more precise control with low voltage electronics is possible. The signal from the pre-amp is fed into the active crossover where it then outputs one signal to each amplifier for each individual speaker driver. So, for example, a stereo 3 way (woofer, mid, tweeter) speaker system will require 3 stereo amplifiers. One amplifier drives the woofers, one drives the mid range, one drives the tweeters. Unlike multi-channel home theatre setups where passive crossovers are generally used and one cable is connected to each speaker box, one active speaker enclosure can sometimes require 3 or 4 sets of cables coming from the amplifiers!