Car Audio Amplifier Essentials: Channels, Power and Clarity

do you need a car amplifier?
Every car stereo system has an amplifier, but adding a separate amp can help reduce distortion. valentinrussanov / E+ / Getty

Car amplifiers suffer from the out of sight, out of mind effect. You don't need to be a car audio expert, or even particularly observant, to point to your car stereo or your speaker grills. The same isn't true of amplifiers, which are often associated with high-performance car audio.

Most car audio systems don't include a separate amplifier, and the easiest car audio upgrades also leave the amplifier out. But the fact is that every single car audio system actually includes an amplifier, and your stereo literally wouldn't work without one.

The fact is that with most car audio systems, the amplifier is built into the head unit. The catch is that they usually aren't very good.

What Are Audio Amplifiers For?

In both home and car audio systems, an amplifier is a device that literally takes a weak audio signal and amplifies it. The signal that goes into the amplifier is too weak to drive speakers, while the signal that comes out can get the job done.

This amplification process is a necessary part of every single home and car audio system, and the power of an amp dictates how loud and distortion-free that the sound will be.

Every system has at least one amp, even if it's built-in to a head unit, and some even include more than one. For instance, it's fairly common to include a dedicated car audio amplifier to drive a subwoofer.

Do You Really Need a Car Audio Amp?

Most head units contain built-in amplifiers, but they’re usually not very powerful. Head units that do contain powerful amps tend more toward the expensive end of the spectrum, at which point it’s often a better choice to just pair a head unit that features preamp outputs with a dedicated amp anyway.

There are a number of reasons to include a separate amplifier component in your car audio system, and you definitely need one if you want:

If you don’t mind a little distortion, and you have no desire to crank your head unit to 11, then you can probably skip the amp and focus on your head unit and speakers. Some head units have enough power to provide relatively distortion-free sound, and adding a high-pass crossover can help clear things up.

Another factor to consider is whether or not your head unit includes preamp outputs. These outputs bypass the built-in amplifier and send a clean signal to an external amplifier.

If your head unit doesn't have preamp outputs, then you'll need to find an amp that features speaker-level inputs. The other option is to use a speaker to line level converter. While both of these methods will tend to introduce noise or distortion, the only other option is to buy a new head unit.

While upgrading your head unit prior to adding an amplifier does involve spending more money, it will provide the best results. When you're working with a decent head unit to begin with, finding the right car amp is a much easier process.

Channels and Other Features

One of the main differentiating factors between amps is how many channels they have. They are available in multiple configurations, from mono to six channels, each of which is best suited to different speaker setups.

At least one channel is needed for each speaker, but it’s also possible to use more than one amp in a single car audio system. For example, a 4-channel amp can power four coaxial speakers, and a separate mono amp can be used for a subwoofer.

There are also different channel configurations that will work best with component speakers, so each amp has to be matched to the system that it’s going to power. Some amps have low pass or high pass filters built right in, which make them perfectly suited to powering woofers or tweeters. Other amps have variable filters, bass boost, and other features.

The Importance of Power

The power of an amp refers to the wattage that it can send to the speakers. Since the whole point of an amplifier is to increase the audio signal strength, the power of an amp is one of its most vital statistics.

The key value here is the RMS, but there is no specific number to look for. The RMS of an amp should be matched to the power handling of the speakers, which is different in every car audio system.

An optimum ratio to shoot for is an RMS that is somewhere between 75 and 150 percent of the power that the speakers can handle, and overpowering the speakers a little is better than severely underpowering them.