Car speaker specifications are similar to home audio speakers. The main difference is that car speakers generally have a lower impedance and higher sensitivity ratings, to compensate for the lower power outputs of car stereo receivers.

The main factors in selecting car speakers are:

Design or Speaker Type
Technical Specifications
Fitting & Mounting

Speaker Design

Design determines the number of individual drivers in a car speaker. Typical combinations are:

a single driver; a woofer and tweeter; a woofer
midrange, tweeter, known as two-way speakers
a woofer, midrange, tweeter, and either an additional midrange or an additional tweeter; known as 3-way and 4-way speakers.

Tweeter Design

Tweeter design is usually either:

Cone Speakers - efficient and the most economical
Dome Speakers - very similar to home audio speakers with smoother, more accurate sound than cone speakers.
Semi-dome Speakers – has a dome inside a cone
Balanced dome Speakers

Whizzer Speakers

Whizzer speakers have a separate tweeter cone driven by the woofer's voice coil

Technical Specifications

Sensitivity: An efficiency or sensitivity rating measures how efficiently speakers convert electrical energy into sound. The higher the number, the louder the speakers will play. Even if you don’t intend to wind up the volume, higher sensitivity ratings mean the speakers are more efficient, mostly resulting in better sound quality.

Frequency Response: The wider the range, the better. Optimal is 20 - 20,000 Hz, the range of human hearing.

RMS Power Range: the range of continuous power the speaker needs/can manage to operate correctly. Use the RMS power range figure to rate and compare different speakers.

Peak Power Handling: the amount of power a speaker can handle during a brief musical burst.

Impedance: represents the "load" the speakers present to the amplifier. The impedance is the resistance to current flow from the amplifier section of your receiver or power amp. Make sure the impedance matches the amplifier capability. Low-impedance speakers (< 4 ohms) or multiple speakers wired in parallel can cause problems with amplifiers not designed to deliver large amounts of current.

Impedance has little impact on sound quality, other than many receivers need a minimum of 4 ohms to work correctly. Most speakers have an impedence of 4 to 8 ohms, with some ranging from 2 to 16 ohms. A higher quality receiver may work with 2 ohms, but other receivers or amplifiers will automatically shut off or blow a fuse. NOTE: a speaker may momentarily fall below its rated impedance at some frequencies.

If you intend to use two pairs of speakers in parallel from the same terminals, choose loudspeakers rated at least 8 ohms.

Mountings

Car audio speakers are either: top mounted or bottom mounted. This refers to the clearance depth required for the speaker to fit properly. This is most important when installing new speakers in a non-factory speaker location.

Advanced Car Speaker Options

Adding to a basic car stereo option typically involves adding subwoofers, amplifiers and crossovers to tailor the output sound to personal tastes.

This does not mean the result is the boorish, obnoxious bass boom boxing that invades the entire neighbourhood. A subwoofer adds quality and purity to music.