A woofer is dedicated to reproduce low-pitched audio frequencies known as bass. Once installed into your car, you should be able to notice a huge difference in sound quality as the volume of the bass line in music increases. One or more woofers are then combined together and mounted in a loudspeaker enclosure, often made of wood, to become a subwoofer. Due to the space limitation in the passenger car, subwoofers are often installed at the boot area or under the rear passenger seats. Subwoofers can be categorised into passive and active. A passive subwoofer has a subwoofer drive and enclosure and is powered by an external amplifier. An active subwoofer, on the other hand, is designed with a built- in amplifier.