Choosing the Head Units 

When you decide to buy a car stereo system or revamping your car’s audio system, start with its music source - the in-dash receiver/player. These are available form car audio specialties such as Kenwood, Pioneer, Alpine, JVC and Sony; in-dash receivers/players improve the overall sound quality of your music system. Most of them come with a CD Player supporting the following formats: CD-R, CD-RW, MP3, and WMA. Some of them even support the Apple iPod and Satellite radio. 

Buy a head unit (in dash receiver) with optional pre-amp output. This is needed when you decide to put an amplifier in future. Buy the head unit with a built-in CD Changer or add a CD Changer to your existing car stereo system so you don't have to fiddle with controls and CD cases while you drive.

Choosing the Speakers

Maximize the sound potential of your car with new car speakers, a car subwoofer, and amplifiers. First measure the areas of your car where you want to place your speakers. When you evaluate item listings, make sure each speaker, subwoofer, and amp will fit in your car. Small cars don’t need more than 4 X 45 Watts power. So the head units’ amplifier is good enough to drive the speakers. Always buy the speakers which are little higher wattage handling capacity than the head units, so that there won’t be any jarring in the speaker units even you keep the sound volume to its maximum.

Manufacturers such as JBL, Alpine, Nippon, Sony and Pioneer deliver a wide range of car speakers, varying in size, price, and power. You can mount them in a variety of places, including the front and/or back of a car, as well as inside car doors.  There are two types of speaker systems, one is the full range speaker and the other is the component system. The full range speaker system has only one speaker handling all the frequency range from 40 Hz to 16,000 Hz. But in component speaker system the frequencies are divided and given to different speakers, which can handle those frequencies efficiently. So the quality of sound is good in component systems rather than the full range speaker system. So go for a component speaker system.

Subwoofers

Sub woofers reproduce very low bass frequencies to provide thumping bass sound. You'll need an amplifier to drive your subwoofer and a place to install an 8- to 15-inch unit. You can mount it in a trunk enclosure, under a seat, or in a side panel or cargo tray, Subwoofers produced by companies such as JBL Audio, Sony, Nippon, Pioneer and Alpine. The larger the subwoofer, the lower the frequency it will produce.

Buy your subwoofer individually, as part of a multi speaker system, or with an enclosure.

Choosing the amplifiers

Car amplifiers add to the overall volume of your car audio system, driving your speakers without causing distortion. Whether you prefer Beethoven or Beck, car amps also improve music clarity and detail. Place a car amplifier under a seat, inside your trunk, or in the rear of your car. Car amplifiers are recommended for big cars with a larger interior space. They come in all ranges from 100 Watts to more than 2000 Watts.