Subwoofers are speakers dedicated solely to reproducing low frequencies. No matter what kind of music you like, or how softly or loudly you like to listen, a quality sub can really improve your overall listening experience. Car speakers are small, so they have trouble producing enough low-frequency sound to give your music realism and depth.
A subwoofer can make the difference between a good-sounding and a great-sounding system. There are a lot of different ways to add a subwoofer to your vehicle. Which one is right for you depends on a lot of different factors, including your musical tastes, budget, and how much space you have available in your vehicle.