There are several things to keep in mind when purchasing new speakers. First, determine whether you want component or coaxial speakers. Component systems consist of separate woofers and tweeters, which provide better overall sound quality than coaxial systems. Coaxial systems are more compact than component systems, so if space is limited in your vehicle, then go with coaxials. Next, think about where you plan on installing them (if there's room) and how many channels you need (one pair per door or two pairs per door). And finally, decide whether you want passive or active speakers—active units require an amplifier while passive ones don't. Functional units provide a lot more power than passive ones and require installation by a professional due to their wiring requirements.