Choosing the Right Amp for Your Car or Truck

JVC Amp

JVC America

Every automotive sound system has an amplifier of some sort, but most 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 an 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 setup.

If you’re looking to upgrade an existing amp or install a brand-new one, be sure to pay attention to these three main factors:

  1. Channels
  2. Power
  3. System compatibility

How Many Channels?

Amplifiers are available in a number of different configurations, and the right number of channels depends on how many speakers you have in your sound system. In general, you 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. There are even mono amplifiers with a class D rating that are specifically designed to use less power and put out less heat when amplifying subwoofers.

Units that have two, four, or six channels are more versatile. You can use a two-channel amp to power two woofers or two coaxial speakers, or you can bridge it to run a single sub or 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 four-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 with enough juice to power them. If you’re just working with your factory speakers, you still should find the RMS (root mean square) value and then choose an amp that’s capable of putting out at least 75 percent 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 multichannel 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.

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 many aftermarket units don’t have preamp outputs. If you’re working with an existing head unit that falls into that category, then you need an amp that has speaker-level inputs. This still will 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 should think about the location and how you will route the wires while you’re still shopping for a unit. Most cars don’t come with amps from the factory, so you’re going to have to find somewhere to fit the new hardware. With that in mind, taking some measurements before you buy an amp can simplify matters.

Some popular installation locations include:

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

Checking the measurements of those spaces ahead of time can save 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 have to provide power to your amp, which means you have to run additional wires.