When you want the best quality in sound reproduction, you need to use 2-way component speakers to produce high and mid-range frequency sounds. Component speakers are designed such that there are four speakers per set. The larger two speakers are designed to produce either mid-range or low (bass) frequencies. The two smaller speakers are designed to produce the high frequencies. This way, the speakers sound better and can handle more power. Component speakers require a part called a crossover or filter. This device splits the input frequency ranges so that the lows go to the big speaker and the highs go to the small speaker.
For more info, see Understanding How Component Car Speakers Work