Constructing your car audio system won't be an easy (or cheap) endeavor. First, you'll need to understand each element of the audio system and know why it's important. Check out our guide to the Top 10 Car Audio Components to get a head start. Having a competitive audio system is all about the quality of the components. Factory-installed coaxial speakers, which mount the high-range tweeters right onto the mid-range woofer, aren't going to cut it -- you'll want a component speaker setup, which separates out the different audio frequencies to produce superior sound quality. Because a component system is expandable, you can -- and should -- add a subwoofer to the mix, as well as an amplifier to give the entire system power. You'll also need a device called an active (or electronic) crossover, which separates the audio signals and delivers them to the proper speakers. Next, seek out some expert guidance on building high-end audio gear into your car. DBD Drag Racing, one organization that holds car audio contests in the United States, has a page dedicated to articles on understanding and building car audio systems.
There are several qualifiers to keep in mind while looking around for high-quality gear. For speakers, you should pay attention to sensitivity and power-handling to make sure the speakers can handle the power being put out by your amplifier [source: Nail]. With subwoofers, pay attention to the RMS power -- a higher RMS rating will guarantee consistent quality.
Now that you have some kind of idea of what parts you'll need, you're one step closer to being ready to upgrade. At this point, you should seek out product reviews for speakers and other components within your price range -- if you want to be truly competitive, they won't come cheap. Thankfully, there are several highly respected brands you can look to for reliable, quality audio. Alpine, Infinity, JL Audio and Eclipse receive high recommendations and positive reviews from many car audio fans. Keep in mind the type of competition you're interested in: If sound pressure is your thing, you'll probably want the most powerful, ear-blasting equipment you can afford. For sound quality, you'll want to read up on reviews and find the highest-rated gear you can, even if it isn't the loudest.