Choosing the Right Amp for Your Car or Truck

Selecting a great external amp is a vital part of building any car audio system. Image courtesy of JVC America

Every automotive sound system has an amplifier of some sort, but most of them aren’t external. The vast majority of these amps are built into head units, and they typically aren’t much to write home about. If you’ve ever cranked up the volume on the stereo and noticed a lot of distortion, one of the main culprits is the underpowered, built-in amp. The power handling characteristics of your speakers also come into play, but a good amp can do wonders even in a stock situation.

If you’re looking to upgrade an existing amp or install a brand new one, there are a few different factors to pay close attention to. Three of the main things to look at are:

  1. Channels
  2. Power
  3. System compatibility

What is the Right Number of Channels?

Amplifiers are available in a number of different configurations, and the right number of channels will depend on how many speakers you have in your sound system. In general, you’ll need one channel for each speaker that you want to amplify. If you’re adding a subwoofer to an existing system, then a single channel amplifier will get the job done just fine. There are even mono amplifiers with a “class D” rating that are specifically designed to use less power and put off less heat when amplifying subwoofers.

Units that have two, four, or six channels are more versatile. A 2-channel amp can be used to power two woofers, two coaxial speakers, or you can bridge it to run a single sub. use it to power two sets of coaxial speakers. If you just want to add a subwoofer and provide more power to your rear full range speakers, then a 4-channel amp will probably do the job. In that case, you can run each full range speaker off its own channel and then bridge the other two to power the sub. On the other hand, you could power all four coaxial speakers off the same amp and then install a separate mono amp for the subwoofer.

Component systems can be more complicated, and you may end up needing more than one amplifier, external crossovers, and other components.

Don't Skimp on Power

If you want to get the best sound out of your car stereo, it’s vital that you don’t underpower your speakers. That’s why a lot of people pick out speakers first and then find an amp that has enough juice to power them. If you’re just working with your factory speakers, you’ll still want to find the RMS value and then choose an amp that’s capable of putting out at least 75 to 150 percent of that number.

Power is also a concern if you’re looking to run a sub off the same amp that you’re using to drive your speakers. Bridging two channels of a multi-channel amp may provide enough power to run a sub, but it isn’t ideal in every situation. If the amp can’t match your specific subwoofer’s power needs, then you’re better off looking for a separate mono amplifier that is capable of doing the job right.

Head Unit and Amplifier Compatibility

If you’re building a car audio system from the ground up, then there’s no question about it: buy a head unit that has preamp outputs and an amplifier that has line level inputs. By providing an unamplified signal to the amp, you’ll end up with the clearest sound possible.

Most factory head units and a lot of aftermarket units don’t have preamp outputs. If you’re working with an existing head unit that falls into that category, then you’ll need to look for an amp that has speaker level inputs. This will still result in better sound than you’d get without the external amp, and it will save you from having to mess around with additional wiring or adapters.

Aftermarket Car Amplifier Installation

Installing and wiring an amplifier isn’t rocket science, but you might want to give a thought to the location and how you will route the wires while you’re still shopping for a unit. Since most cars don’t come with amps from the factory, you’re going to have to find somewhere to fit the new hardware. With that in mind, it can simplify matters if you take some measurements before you buy an amp.

Some popular installation locations include:

  • Under one of the seats
  • In the trunk
  • Against the passenger-side firewall

If you check the measurements of those spaces ahead of time, you can save yourself a lot of grief down the line. The same goes for installing component speakers and subwoofers, which typically won’t have been accounted for in the design of your vehicle.

Also keep in mind that you’ll need to provide power to your amp, which means you’ll have to run additional wires.