So what are your options?
Need to replace old or broken speakers?
New speakers improve the entire range of your sound, from deeper bass to more well-defined highs. Best of all, they're easy to install and usually more affordable than replacing the receiver. Most factory installed car speakers are made of lightweight paper or other cheap-to-produce materials in order to keep down the purchase price of your vehicle. They also tend to distort and wear down a lot faster than aftermarket speakers, so even if your speakers sounded good when you bought the car, they've probably changed after a few years.
Aftermarket speakers are made of higher quality materials for a more faithful reproduction of sound and for added durability. Full-range speakers (some combination of a woofer, a midrange, and/or a tweeter) fit easily into your car's factory locations and are probably your best bet for improved sound. If you want to hear all that your music has to offer, use a set of component speakers with separate woofers and tweeters to transform your car into a concert soundstage.
Does your music need a little more "umph?"
You need to give your speakers more power. An amplifier increases the volume of your system without distorting it, so you'll have no trouble hearing your tunes with the windows down and the sunroof open. Amplifiers also give your music life by bringing out musical details and clarity, resulting in better sound quality at all volume levels.
Drive a noisy car?
Is your music competing with your muffler for your attention? You should look into vibration damping materials ? a little Dynamat in your vehicle can go a long way in reducing the interior noise level.
Do you want to feel the beat?
If you like your sound, but want some added depth, a subwoofer is a great addition to any system. Augmenting your setup with a subwoofer driven by an appropriate amplifier, for instance, will fill in the low notes that small full-range speakers aren't designed to hit, giving you a richer overall sound. You can choose from component subs to customize your sound or preloaded enclosures for easy installation.
If you want a sub, but are concerned about how much space it might take up in your car, then you might want a vehicle-specific subwoofer enclosure. They mount in your cargo area or under a seat, so you don't lose much storage space.
What is your music style?
Think about what kind of music you listen to, and especially how you listen to your music. If you like it loud and heavy, you're going to want outboard amplifiers and a subwoofer or two for sure. Is soft classical music your style? A new receiver should provide plenty of RMS wattage to full-range speakers — though you would certainly still benefit from the low-frequency output of a subwoofer.
