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The Car Amplifier Buying Guide

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Your Guide to Choosing the Right Car Stereo Amplifier for Your Vehicle

So you’re in the market for an aftermarket car amplifier. You’ve probably decided that it’s time to upgrade the sound of your car stereo system. And one of the components you need to do so is the powerful amplifier.

An amp that is powerful enough and matches your other components will make a huge difference in the quality of sound coming from your car stereo. 

But the type of amp you choose will depend on a number of factors, like your speakers, whether you’re using a subwoofer, and where you plan to install the amp in your car.

So consider this guide, along with everything you need to know about car amplifiers, to help you make an informed decision when you’re ready to buy your new powerful car amplifier.


Amps enhance your overall car stereo system by offering the following benefits:

Improved Sound Quality

An aftermarket amp provides a clean power source to your speakers without straining or distortion. Unlike the amps built into existing car stereo head units, aftermarket amps are designed without making any compromises for limited space. The improved design allows for clean, clear sound at all volume levels.

Properly Powers Upgraded Speakers

If you’re upgrading to high-quality speakers in your car sound system, you won’t want to rely on the amp in the factory head unit to power these speakers. Aftermarket speakers and component systems tend to need more power for peak performance than you can get from your built-in amp and head unit.

Power for Subwoofers

A subwoofer requires much more power than an existing head unit amp can provide. So if you plan to upgrade your car stereo system with a subwoofer, you will need a separate amp to provide enough power the subwoofer.


When shopping for an amp, you’ll need to find one that is compatible with your other car audio system components.

Matching Impedance for the Subwoofer Amplifier

Make sure the power of your amp matches your subwoofer’s power requirements—which is known as impedance and is represented in ohms. For example, a 2-ohm subwoofer needs an amp that is stable down to 2 ohms or less.

Matching the Head Unit

If you’re building an aftermarket car audio system, use a head unit with preamp outputs and an amp with line-level inputs. This setup will send an unamplified signal to the amp and create the best and clearest sound possible.

But if you’re using an existing head unit that doesn’t have preamp outputs, use an amp with speaker-level inputs to improve the sound.

You’ll also need to match the number of channels on your amp to the number of speakers you have, along with matching the amp’s power output to the speakers’ power handling.


The number of channels you need on your car amplifier depends on the number of speakers you have in your car sound system. Generally, you need one channel per speaker.

1 Channel – Mono Channel

If you are adding a subwoofer to your sound system, a single-channel (or mono) amplifier will power your subwoofer. Consider a mono amp with a Class D rating for your sub. These use less power and emit less heat.

2 Channels

Two- and four-channel amps are mostly used to power door speakers.

A two-channel amp can power:

  • Two coaxial speakers;
  • Two woofers; or,
  • You can also bridge this amp to power a single subwoofer or two sets of coaxial speakers.

3 Channels

A three-channel amp is perfect for powering a pair of speakers and a subwoofer. This configuration is ideal if you only want to power your front or rear speakers with an aftermarket amp.

4 Channels

A four-channel amp works to power:

  • Four speakers;
  • Two speakers and a subwoofer—you can use a four-channel amp to power a subwoofer and two rear full-range speakers by bridging two of the channels to power the sub.

If you want to add a subwoofer, you also can use a four-channel amp to power your four coaxial speakers and a mono-channel amp to power your subwoofer.

5+ Channels

An amp with five channels can power your entire car audio system:

  • Two speakers in the front;
  • Two speakers in the rear; and,
  • One subwoofer.

Amps with 6 to 8 channels are designed for powering 3- and 4-way active systems, with an amp channel dedicated to each driver—e.g., tweeters and midrange speakers—and two channels bridged together to power a sub.


You’ll want to find amps that have enough power to get the best sound out of your speakers. Whether you are upgrading your speakers or using your vehicle’s existing speakers, make sure the power of your amp matches the speakers, so you don’t risk under-powering the speakers.

Look for the continuous RMS (root mean square) power rating on your speakers. The RMS is usually a ranging value, e.g., 5-60 watts RMS. Take the top number of the RMS rating and find an amp that can put out 75 to 150 percent of that number. To calculate 75 percent of that number, multiply it by 0.75. And to find 150 percent of that number, multiply by 1.5.

For example, a speaker with a power handling of 200 watts needs an amp with a power rating between 150 and 300 watts.


When shopping for an amp, you also need to think about the installation location and how you will route the wires. You should first find a convenient space in your vehicle to install the amp. And then you can shop for an amp that will fit that space.

So choose an amp location in your car and measure the space before you go amp shopping, so you know what size of amp to look for (the same goes for installing component speakers and subwoofers).

Here are common amp installation spots in vehicles:

  • Against the passenger-side firewall;
  • Under the seats;
  • In the trunk.

For more information on car amplifier installation, check out our step-by-step guide for installing your car stereo amplifier.

Now that you know the basics of choosing an amp contact your local car audio experts for help installing the best amp to pump up the sound in your car stereo system.

About AudioMotive

For over 10 years, AudioMotive has and continues to be, Ottawa’s premier vehicle upgrade experts. With more than 25 years of combined industry experience, we proudly specialize in all things related to HID lighting and mobile electronics sales and installation.