The size classification for speakers, measured in inches. Round speakers have one figure, while oval speakers are sized by the short axis "x" the long axis (ex. 6x8). To be sure you select speakers that will fit your car, identify your vehicle and choose the proper speaker location (see the "Please select your car" link).
The number of individual drivers in a car speaker. (1) single driver; (2) woofer and tweeter; (3) woofer, midrange, tweeter; (4) woofer, midrange, tweeter, and either an additional midrange or an additional tweeter.
Commonly, speakers with two drivers are called "Two-Way" speakers, while speakers with three and four drivers are called "Three-Way" and "Four-Way," respectively.
Speakers with a "Whizzer cone" tweeter (a tweeter that shares a voice coil with the woofer) are referred to as "Dual Cone" speakers.
Max RMS Power
The maximum amount of continuous (RMS) power that can be fed to the speakers. Providing speakers with power in excess of this rating can damage them.
An efficiency or sensitivity rating tells you how efficiently speakers converts power into sound. The higher the number, the louder the speakers will play. An efficient speaker helps you maximize your available power.