Q: What's the difference between passive and active crossovers?
A: There are two types of crossovers — "passive" and "active" (also referred to as "electronic"). A passive crossover is basically a capacitor or coil installed on the speaker leads between an amplifier and a speaker. It sets up a roadblock to stop certain frequencies from reaching the speakers. Passive crossovers are relatively inexpensive and easy to install. Their primary disadvantage is that they tend to make your overall system slightly inefficient because they filter out signals that have already been amplified.
Your system will perform better and be more efficient using an electronic crossover, especially if you're running multiple amps. An electronic crossover is installed between your receiver or equalizer and your amplifiers. It filters and directs the frequency bands in the low level signal before they reach the amplifiers.
Active crossovers are usually adjustable (you can select the crossover points) and often have other features like bass boost circuits and phase switches for subwoofers. Another bonus when using an electronic crossover is that you can independently control the relative volume of different types of speakers.