A head unit usually consists of a combination of a radio, tape player, or CD/DVD player. Newer head units are now emphasizing on digital music support (MP3, WMA, and AAC formats) and USB, Bluetooth, and Wi-Fi connectivity.
Most modern cars include at least a CD player/ CD recorder, and some have the option for car stereo CD changers, which hold multiple disks either in the head unit itself or in a separate unit usually located in a trunk or console. The main types of CD changers are External Cartridge, Internal Cartridge and Carousel CD changers.
The stereophonic sound, commonly called stereo, is the independent reproduction of the sound using two or more channels audio in way to create a natural impression of the heard sound from several directions, similar to that one in the natural hearing. In popular use, stereo audio of the car means generally the recording of 2 sounds on 2 channels and the reproduction of the sound using the data for more than a loudspeaker simultaneously.
Before stereo radio, speakers were often located in the middle of the dashboard through perforations pointed at the front windshield. When stereo systems became available, car audio speakers came to be located in doors and in the rear of the vehicle in parcel shelves. In modern cars, kick panel enclosures are used for high-end and competition stereo systems and allow for larger drivers and better driver placement.
The amplifiers are used to drive the speakers. These provide the necessary music power, which is measured in watts. An amplifier is a very important component of good car audio speakers system. One should always ensure that the total power handling capacity of the speakers connected to the amplifier or head unit is greater than the power of the amplifier or head unit.
