A device that separates incoming sound signals into separate frequency bands and reproduces them on more than one loudspeaker driver, powered by multiple amplifiers, is an active crossover. They are distinguished from passive crossovers, which make use of a single amplifier to power each respective driver.
A loudspeaker generally features between two and four separate drivers for reproducing sound, according to Lenard Audio Institute. Crossovers separate incoming sound signals by their frequency in order to produce the most faithful representation of the sound signal received. The difference in sound quality between active and passive crossovers is immediately noticeable by anyone who makes a comparison.
Woofers are the largest drivers in a loudspeaker system, being dedicated to bass tones. Horns and tweeters reproduce middle frequency and high frequency sounds, respectively. An active crossover routes incoming sound signals toward these separate drivers while amplifying each one individually.
The use of an individual amplifier for each driver allows an audio engineer to exert a greater degree of control over the quality of the signal each driver receives. One of the primary benefits of this control is the ability to set specific speaker impedance ratings for each driver, as described by Elliot Sound Products.