If you don't own a car with a custom stereo or any type of musical instrument than you probably are not aware of what an amplifier is and what it does. An amplifier is simply a piece of electronic equipment that takes the sound produced from a musical instrument or a stereo and increases or amplifies that signal and that electronic output comes through the speaker.
An amplifier is necessary for many musical instruments in order to connect them to speakers. Amplifiers also help produce unique sounds that you hear many musicians play, most notably guitar players.
|Mixing Amplifier MA-35 (Photo credit: Wikipedia)|
Most guitar players can people with car stereos basically just want an amplifier to produce very loud sounds without a lot of distortion of the sound.
How good the amplifier is depends on a number of specifications. The gain is the ratio between the output and the input and is usually measured in decibels.
Bandwidth is another important specification to consider. It is the range of frequencies that the amplifier can produce.
Another quality to consider it the efficiency, especially for car stereos. The efficiency tells you how much of the power that goes to the amplifier is actually applied to the output. Class A amplifier are the most inefficient, while Class AB amps are the best.
The bottom line is that people use amplifiers to make their cars and musical instruments sound very allow. More sophisticated musicians buy amplifiers to produce a higher and richer sound than what the instrument could produce just by itself.