The car audio amplifier... its soul purpose is to take a low level signal from the source unit and transform it into a high level signal for activating the loudspeakers.

Amplifiers range in power from about twenty watts per channel to over one thousand watts per channel. Would you believe that the prices range anywhere from fifty dollars to several thousand dollars depending on features, power output and quality! Amplifiers range from one channel of output to as many as eight channels. The most common amplifiers are currently two and four channel models.

Amplifier Power Ratings Power amplifiers also have "optional equipment". These features include built-in active crossovers, equalizers, signal processing and speaker level inputs. When shopping for an amplifier consider that all power ratings are not created equal. The only true measure of an amplifier's power is its continuous power rating or R.M.S. rating ( or root mean square) and refers to the average power output of the amplifiers. Some of the low-quality brands will exaggerate or even outright lie about the power output of their amplifiers which is a good reason to stick with the well known manufacturers.

Car Amplifier Quality: Also keep in mind the quality of the amplifier. A generally good indication of quality build and the power output is the size and the weight of the amplifier itself. Better quality amplifiers will usually have a heavier and larger heatsink versus a low quality amplifier of the same power rating.

However there are many top quality amplifiers that do not follow this rule.

Blaupunkt makes a line of amplifiers that have a plastic shell. Because of the high efficiency design of those amplifiers a heavy heatsink is not required. Also a good indication of an amplifier's true output is the size of the fuse used.

Use your head when buying and keep in mind the brand's reputation for quality.

If you find yourself on a budget or lack space for many components then the economical thing to do is buy a multi-channel amplifier with the built in features and processors that you desire. By minimizing the number of components the chance of noise entering into the system is lessened.

Some features and aspects of amplifiers to consider are:

Bridgeable: This feature allows a pair of amplifier power channels to be combined into one channel of greater power. This is usually used for driving a subwoofer although it will work with any other type of speaker as well

Channels: The more channels an amplifier has the greater the installation flexibility it will have. Especially in terms of options, future add-ons and upgrades.

Class: This refers to the way the amplifier operates. The three types that are most likely to be encountered are A, A/B, and D. Class A amplifiers are the least efficient in terms of power consumption, staying on continually, but also have better sound in general than A/B amplifiers. They are very rare in car audio. Class A/B amplifiers are more efficient than the class A design and are the most common type. Almost all amplifiers in the car audio market are of the A/B design. Class D amplifiers are usually reserved for high power subwoofer amplifiers and can reach efficiencies in the 80% range. This design can therefore be smaller, uses less current and produces less heat than the other classes.

Connectors: This is the method of attachment used for wires that are connected to the amplifier, including speaker and power wires. The most common kind is the screw terminal strip. This is a series of screw connectors that can be removed and replaced without compromising the amplifier. The other main type of attachment is the "Molex" type connector. This method involves a wire harness that plugs into the amplifier after the power and speaker connections have been made with a crimp or solder connection. If the amplifier is installed in more than one system these wires can get pretty short over time and become more difficult and even dangerous to work with. A variation on the two is a harness that the power and speaker wires screw into. Then the harness plugs into the amplifier. This is probably the most convenient of all connections.

Crossover/Filter: A built in crossover can be useful, especially if it is many frequencies of adjustment. A filter is a crossover that only affects one channel, not actually splitting frequencies but simply reducing a range of them.

Distortion: This is often given as T.H.D. or total harmonic distortion. It is the measure of how much an amplifier will change a signal from the input signal it is given. Figures below 0.1% are negligible and will not be heard. Usually the figure can be in the 3% range without being heard but virtually all high quality amplifiers will have a T.H.D. below 0.1%.

Efficiency: This is the ratio of of power input (from the battery) to power output (to the speakers). A 100 watt amplifier with an efficiency of 50% would take in 200 watts of power from the battery and output 100 watts of power to the speakers. The other 100 watts of power would be wasted as heat. The higher the efficiency of an amplifier the better.
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