ideally,, in having a new audio system is you purchase a new head unit, speakers, sub and amp. you can buy a full range speakers in the front or buy a component speakers which sound better than full range.. the rear speakers usually are 6x9 speakers. then buy an amp and sub and match their impedance and rms rating.. this is roughly how you do it,, but it becomes more complex as you study on how to get the maximum sound quality in your car audio system.
