A crossover is an electronics device that takes a single input signal and creates two or three output signals consisting of different ranges of frequencies (highs, mids, and lows), so tweeters, woofers, and subwoofers will each get only the range of frequencies they were designed to play. The main purpose of breaking music into separated bands of frequencies, and only sending certain frequencies to specific speakers, or “drivers,” is to effectively reduce distortion and achieve higher audio fidelity. Because otherwise, a messy, sonic “traffic jam” results. Within each crossover, a low-pass filter blocks the highs but passes the lows to the woofer, while a high-pass filter blocks the lows and passes high frequency notes on to the tweeters. Crossovers for 3-way systems consisting of tweeters, midrange drivers, and subwoofers, include, besides high- and low-pass filters, “bandpass” filters which handle frequencies between two points by utilizing both a high-pass and low-pass in the same filter network. So, for example you could have a midrange driver that handle frequencies between 100 Hz to 2500 Hz. So, if you want to build a car audio system that sounds clear and harmonious, consider using a car audio crossover. The Audiotek CX3 is one of the best passive car audio crossovers you can buy. This thing is housed in a steel casing with a bottom made of see through plexiglass allowing a view of the inner components. It’s small and compact enough to fit into some sort of nook and cranny in most vehicles.