Most cars, especially ones manufactured 10+ years ago, have crude and very annoying to listen sound systems and tape deck players. For some time invested and a little cash you can have a mobile entertainment center in your car.
There are many brands and options there. Kenwood, Pioneer, JL audio and Sony are top of the line in this category.
No matter how much you spending on an amp or a head unit, if you have low quality speakers, you will get low quality sound. Speakers come from 1″ tweeters to 15″+ subwoofers. Generally, a smaller speaker gives clearer highs and bigger speakers give deeper lows. Mid-range speakers come in 2 way (plays high and low) and 3 way (plays highs mid and lows).
8″ subs don’t bump, 10″ give a jitter, 12 shake rattle n roll.
system. A low quality or low power amp matched to high would not take full advantage of the speakers quality. A too powerful amp will blow your speakers in a couple months.