Audio crossover

Audio crossovers are a type of electronic filter circuitry used in a range of audio applications, to split up an audio signal into two or more frequency ranges, so that the signals can be sent to drivers or tweeters that are designed for different frequency ranges. Crossovers are often described as "two-way" or "three-way", which indicate, respectively, that the crossover splits a given signal into two frequency ranges or three frequency ranges. Crossovers are used in loudspeaker cabinets, power amplifiers in consumer electronics (hi-fi, home cinema sound and car audio) and pro audio and musical instrument amplifier products. For the latter two markets, crossovers are used in bass amplifiers, keyboard amplifiers, bass and keyboard speaker enclosures and sound reinforcement system equipment (PA speakers, monitor speakers, subwoofer systems, etc.).

Crossovers are used because most individual loudspeaker drivers are incapable of covering the entire audio spectrum from low frequencies to high frequencies with acceptable relative volume and absence of distortion. Most hi-fi speaker systems and sound reinforcement system speaker cabinets combination of multiple loudspeaker drivers, each catering to a different frequency band. A standard simple example is hi-fi and PA system cabinets that contain a woofer for low and mid frequencies and a tweeter for high frequencies. Since a sound signal source, be it recorded music from a CD player or a live band's mix from an audio console has all of the low, mid and high frequencies combined, a crossover circuit is used to split the audio signal into separate frequency bands that can be separately routed to loudspeakers, tweeters or horns optimized for those frequency bands.

...
Wikipedia