A subwoofer is basically a loudspeaker which is used for the reproduction of lower pitched sounds like the bass or the human voice. They complement the loudspeakers by devoting itself to covering the lower sounds while the main speakers reproduce the louder and higher ranges. Though they are usually made up of different materials like wood, plastic and have many other features, subs can be passive as well as active. Passive subs have an enclosure and are driven by an external amplifier through a driver, while active subs have a built-in amplifier. Though they were made in the 1960's, these instruments were specifically designed to optimize the bass sounds. Their use was further recognized during the dawn of Sensurround. Since then, subwoofers have been utilized by cinemas, amusement parks, home theatre and of course the car audio system.

In the car audio system, the subs are usually hidden behind the upholstery. Due to a limited space inside a car, the common places where they are installed are in the dashboard, passenger seats and even on the inner door panels. For larger and bulkier subs, they are commonly installed on the back seat or most typically inside the car trunk. Concerns have risen however for car audio systems that produce too much sound and subs have played a vital role in it. Car audio setups that are too loud are mostly designed for competitions; too much exposure to these sound levels can cause hearing loss and doing it while driving can lead to accidents.

The basic build up and components of a mobile car sub and a common sub varies very little. The main factor however for its differences is that mobile subs have more emphasis on its outward appearance. As with any other car audio components, aesthetics matter a lot. Recently, car audio sub manufacturers have been able to produce non-circular sub designs in terms of enclosures and the sub itself. There are a lot of designs available in the aftermarket nowadays and the visual appearance may come in uniformed together with the other components and accessories or may be unique in terms of the grills, the paintjob, lights and LED displays, some are even preordered and then customized.

Subwoofers are made usually at a range of 8 inches, 10 inches, 12 inches and some even reach up to 18 – 32 inches in diameter.  The subs capability to produce the sound is very crucial that is why the depth of its compartment must be adjusted accordingly. Buyers are now also considering space designs that allow the sound pressure to be resonated well while the cooling of the motor is well allocated also.