The four components of the car audio system are the head units, amplifiers, speakers and auxiliary input devices. This input devices are CD changer or graphic equalizer. The main part is head unit which makes the audio system work. The head unit consists of the other remaining three parts in some audio systems, but in other models they come separately. The signal boosters are amplifiers.
You can compare these things, such as:
The main thing is sound quality for audio system. There are new model audio systems with crisp and clear sound system. There are only two speaker of some model of the audio systems, they are kept near the driver and front of the passenger side. There are four more speakers with other model of audio systems and they are kept in various areas of the car.
There are different shapes or forms of controls for audio system of the car. There are fewer controls and limited to the radio channels and control of the volume , if it is less expensive model. If it the higher price model then more the system has to offer. Suppose, it it is mid priced audio system then there are CD controller. Instead of the traditional knobs, there are push buttons on the CD controller. And also it shows the time and channels. If it high priced model then there is a bigger display unit which shows the time and channels and music information, it shows singer or band on a CD as music information.
So, you compare sound quality and control systems of the audio systems of the car. In this way you can compare and choose one which is right for you.