An amplifier is really a simple piece of your aftermarket sound system. A car amplifier basically amplifies a signal from a source (in the case of a car sound system, your stereo) to a much greater signal. Signals from source units are typically fairly low voltage, which is fine for most speakers (but not subwoofers), amplifying your speakers will make them perform to their full potential. Now, your speakers can be powered by just your source unit, but a subwoofer will require an amplifier. Giving your system more power will improve both sound quality and how loud your system will play.
When looking for an amplifier, it’s important to know what you intend to use it for. If you’re simply adding a subwoofer to your system you will only need a monoblock amp while with a complete system (4 speakers and a subwoofer) your best bet is either a 4 channel and a monoblock or a 5 channel amplifier. It is critical to the success of your sound system that you match up all of your equipment (speakers, subwoofer, source unit) with the right amplifier to make sure everything is powered properly to give you the best sound possible.
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