Car amplifier buying guide

Get the wattage and number of channels you need

By

Buck Pomerantz

Buck Pomerantz was born and raised in Philadelphia. His parents bought their first television set when he was born. He figured out how to run it by the time he was two. Besides athletics, his formative interests included electronics, amateur radio, music, and stage crew work. He got his BA in writing from Brown University. Then he joined a rock 'n roll band as their soundman and moved to Charlottesville, Virginia. After that venture failed, he spent time in Boston, New Orleans, and Berkeley. He worked in a music store in Austin manufacturing, installing, repairing, and operating sound systems for recording studios, clubs, and bands. He moved back to Charlottesville, ran a little recording studio and finally joined Crutchfield as a copywriter. He has 2 grown children and 3 grandchildren, but after a good nap he can still rock out.

More from Buck Pomerantz

Kicker 40KX2400.1

Kicker's 2,400-watt 40KX2400.1 subwoofer amplifier delivers competition-level bass with style

Why add an amplifier?

If you want your music to be loud, amplifiers are definitely part of the picture. But whether you run your system wide open or softly enough for conversation, a power amplifier will breathe life into your music, bringing out all of its excitement and detail. Here are a few of the main benefits of adding an amp:

  • Better sound quality — Adding an amplifier gives you a clean power source that can drive your speakers without straining. Unlike an amplifier built into an in-dash stereo, an external power amp isn't limited by the space available — it can be designed without compromises. That means your music will sound cleaner and more defined at all volume levels.
  • Power for upgraded speakers — A factory system or an in-dash receiver may not do justice to your upgraded speakers. If you're adding high-quality aftermarket speakers or component systems to your vehicle, they may require more power for peak performance than your existing in-dash receiver can provide.
  • Powering a subwoofer — Subwoofers require significantly more power than a brand-name or factory in-dash receiver can provide. A separate amp is a necessity.
Rockford Fosgate PBR300X4

The untra-compact 4-channel Rockford Fosgate PBR300X4 amplifier fits almost anywhere.

I want to add some oomph to a factory system

Standard factory car stereos usually have no more than about 10 watts RMS maximum output power per channel, in spite of what the car dealers advertise. That's usually not enough power to overcome road noise without sounding shrill. A great way to upgrade your sound system without changing the factory look of your vehicle is to get a factory system upgrade. Each of these systems include an amplifier and other sound processing gear custom-designed for your specific vehicle that will vastly improve the sound and leave the interior looking stock.

A more economical way to upgrade your sound system without changing the factory receiver or speakers is to get a compact 4-channel amp to boost the power for your front and rear speakers. The Alpine KTP-445U Power Pack and the Clarion XC1410 4-channel amp are two examples of amplifiers that are small enough that they can be installed behind many dashboards and powerful enough to dramatically increase the quality and clarity of your sound. Both of these amps, as well as many others available at Crutchfield, feature inputs that can handle the high-level signal from the vehicle's factory speaker wiring. Look for an amplifier with "speaker-level inputs" as one of its features if you want to add it to a factory system.

DIY Installation Help

Amplifiers don't come with the wiring you need to connect them to your stereo.

Wiring kits provide everything you need to send signal and power to your amp.

You'll also need speaker wire to send signal from your amp to your existing speakers.

A capacitor stores reserve power and delivers it when your amp needs it most.

And don't forget the extra hardware you might need for a truly professional installation: battery terminals, power distribution hardware, fuses, etc.

I want my aftermarket speakers to really sing

All aftermarket speakers, especially component sets, benefit from being fed more power than what a factory or even an aftermarket receiver can put out. Among a speaker's published specifications you will find its RMS (or "continuous") power rating, usually as a range — "5-60 watts RMS power range" for example. The higher number represents the approximate driving power at which the speaker will play at its fullest and best according to the manufacturer. Actually, most speakers get rated very conservatively and can take a lot more power than their rating (as much as 150% of the rating is usually safe). But they really won't sound good unless they're able to get at least 3-quarters (75%) of that power rating.

So, if you already have aftermarket speakers, find out their top RMS rating. Pairs should be the same, but if your front and rear pairs are slightly different, it's okay — use the lower rating. Multiply that number by 75% (0.75) — this is the minimum RMS wattage the amp you're looking for should have per channel. Now, multiply that rating number by 150% (1.5) — this is the maximum output power per channel you'll want for your amp. Don't worry if you can't find an amp small enough to match speakers with low power ratings. You can always set your amplifier's gain low enough that it won't ever attain its full power, so your speakers will be safe.

Many people like their music with a strong front stage and don't even use rear speakers. A 2-channel amplifier will be the practical solution when you only need to power a single pair of speakers. But if you like rear-fill sound in your car and want to retain front-to-rear fade control, get a 4-channel amp — one channel for each speaker.

There are some other amp configurations to consider for when you want to include a subwoofer in your system. A 3-channel amp can take care of a single pair of speakers plus a sub quite effectively. A 4-channel amp can also be employed to run a pair of speakers and a sub — two channels bridged together to run the sub and the other two to drive the speakers. This gives you the option for future expansion of your system, allowing you to later change the amp over to run four speakers and add a separate amp for the sub.

Alpine PDR-V75

Alpine's PDR-V75 5-channel amp can power your front and rear speakers along with a sub.

You may want to consider a 5-channel amplifier that can power your entire system from one convenient and compact package. Some manufacturers offer 6- and 8-channel amps. These were designed to run 3- and 4-way active systems, with amplifier channels dedicated to one driver each, like a tweeter or a midrange speaker, and a couple channels bridged together to run a sub.

I plan to get new speakers along with my new amp

When building a system from scratch, one of the first questions you should ask yourself is, "How loud do I want this to be?" Car audio systems don't necessarily need massive amounts of amp wattage to sound loud, but having a lot of power available is good for the "headroom" of a system, the ability to deliver an emotionally impactful burst when the music asks for one. There's also the interior size of your vehicle to consider.

Sound Ordnance M4050

A Sound Ordnance M4050 4-channel amp is an economical way to amplify your system.

If you drive a compact coupe or hatchback, a sports car, or a small-cab pickup, for instance, a 50 watts RMS per channel, or smaller, amp will probably do fine, overcoming road noises and adding clarity to your music. Look for speakers with a top RMS rating of at least 35 watts RMS (using the 75%/150% rule) to go along with the amp.

For larger vehicles and for those who just want more volume, you should step up to at least a 75 watts RMS per channel setup. A difference of 5 or 10 watts either way won't make any difference and probably can't even be heard. Matching speakers will need to each have a top RMS rating of 50 watts RMS or more.

Those of you who want even greater impact and eye-popping volume out of your system will want to go for an amp with 100 watts RMS or more per channel. Get speakers or component sets rated for at least 75 watts RMS each.

I'm just adding a subwoofer

Bass is much harder to amplify than the rest of the spectrum of sound — that's why there are so many large and beefy subwoofer amplifiers out there dedicated solely to reproducing bass. Mono, 1-channel amps are designed for subwoofers, will work with a wide range of impedances, and have tone controls and filters specifically made to help reproduce bass. Although many 2- and 4-channel amps can be bridged to increase their power enough to run a sub, they often then can't handle the sub's low impedance, and overheat or go into protect mode.

You want the bass to musically blend and be well-balanced with the rest of your system, so, here's a good rule-of-thumb guide to sub power:

  • If you're using your car's factory stereo — 50 to 200 watts RMS of power for the bass will do nicely.
  • An aftermarket receiver — you might want 200 to 300 watts RMS of power for your sub.
  • Amplified speakers with around 50 watts RMS per channel — plan on 250 to 500 watts RMS for bass
  • A 100 watts RMS or higher per channel system — you'll want at least 1,000 watts RMS for your sub.
JL Audio XD600/1v2

JL Audio's XD600/1v2 subwoofer amp puts out up to 600 watts RMS for bass.

You'll need to impedance match your sub amp and sub. It would be a shame and a waste of money to buy a couple of subwoofers and an amplifier, for instance, only to find out that the amp can't run the subs because wired together, their impedance would be too low for the amp to run without overheating. Remember, if you're adding a sub to a factory system, get a subwoofer amp with speaker-level inputs, so it can get its signal from the factory speaker wires.

Need more help?

Browse our entire selection of car amplifiers. If you need more help, give our Advisors a call at 1-888-955-6000. They have the knowledge and experience to help you find an amp that will meet your needs.

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