What is a Car Subwoofer Crossover?
A car subwoofer crossover is defined as a filter and director of frequencies in order to allow only a certain amount of frequencies to reach a specific speaker. Frequencies that occur outside of the range of the filter, or the crossover, are blocked from the speakers. This blocking is also known as attenuating. Every type of stereo system for a vehicle needs some form of a crossover to monitor and regulate the frequencies that are put out by the stereo system. You can set up a crossover based on what type of stereo system you are installing in your vehicle.
For more info, see How to Find Good Car Subwoofer Speakers