How improve the sound of a stock car head unit?

1)Upgrade your front car speakers and rear speakers will improve sound quality.Stock car speakers are made out of cheap paper cone.Most aftermarket speakers are made and designed better than crappy cheap stock speakers.Make sure you look for speakers with tweeters as this can enhance the sound and deliver high frequency sounds to your ear.

2)If your car radio has any settings that lets you control the bass, balance and treble tweak with them to increase sound quality.

3)Turn the volume down until you hear less distortion.Most stock car cd player that come with the car have cheap built in mosfet amplifiers that deliver poor sound quality and high volumes.Its better to upgrade your stock head unit with a aftermarket replacement because believe me you will notice more loudness and sound quality.