The difference between two- and four-way car speakers is a matter of sound frequency separation. Also called "full-range" speakers, they include multiple speakers within a single speaker mount, called the "basket." Three-way speakers are also commonly used for car stereos.
Sound frequencies are measured in Hertz (Hz), of which 20 to 20,000 Hz (low frequency to high) are audible to human ears. Frequencies are separated by an electronic crossover, and distributed to speakers that are best suited for specific frequency reproduction. Full range speakers typically include a built-in crossover.
Two-way speakers contain a large main speaker called a "woofer" for reproduction of the low- and mid-range frequencies, and an integrated "tweeter" for high frequency reproduction. Two-way speakers are also called "co-axial" speakers.
Three-way speakers contain a woofer for reproduction of the low-frequencies, a smaller mid-range speaker for mid-range frequencies, and a tweeter for high frequencies. Three-way speakers are also called "tri-axial" speakers.
Four-way speakers include woofer, mid-range, and tweeter, with the addition of a "super-tweeter" for very high frequencies.
Full-range speakers offer space-saving and wiring simplicity advantages. In component systems where separate speakers are used for each frequency, multiple installation areas in the car are necessary, as are wires for each speaker.
Which is Best?
Your ears are the best judge of speaker sound. Every car is different, and speakers vary in sound quality due to speaker and magnet materials, construction methods, crossover and the type of music to which you're listening.