An abbreviation for “crossover network,” which divides an audio signal into multiple frequency bands. This is done to optimize which frequencies are directed to multiple speaker drivers, for example, a woofer for low frequencies and a tweeter for high frequencies.
The frequency where the sound is divided is called the “crossover frequency.” Ideally, when a crossover network is used in a speaker enclosure, a crossover frequency is chosen that protects the tweeter, allowing it to produce only those frequencies that it can reproduce the best, and allows both the response and coverage pattern of the woofer to blend well with the tweeter.