How to Choose a Car Amplifier

Why you need an amplifier at all

Your head unit (the stereo in your dash) is rated for roughly 15–22 watts RMS per channel. That is enough for background listening, but the moment you turn the volume up, that little internal amp runs out of headroom and the sound gets harsh and distorted. Distortion, not loudness, is what blows speakers.

An external amplifier delivers clean power at volume. Clean power means your speakers can hit their peaks without the signal falling apart, so the music stays detailed even when it is loud. If you have upgraded your speakers or you want to add a subwoofer, an amp is not optional — it is the upgrade.

Match the amp to your speakers

The single most common mistake is buying an amp that does not match the speakers. Three things have to line up: power (RMS watts), impedance (ohms), and channel count.

For power, aim for an amp rated at roughly 75–150% of your speakers’ RMS rating. Under-powering slightly is safe; massively over-powering is where speakers get cooked. For impedance, check what your speakers are rated for (commonly 4 ohms, sometimes 2) and make sure the amp is rated to drive that load at that impedance.

Channel count depends on what you are driving: a 2-channel amp for a pair of front speakers, a 4-channel amp for front and rear, and a mono (1-channel) amp for a subwoofer. If you want one box to run speakers and a sub, look for a 5-channel amp.

Class D vs Class AB

Amplifier class describes how the power circuit works. Class AB is the older, analog design — it sounds warm and clean but is bulky and runs hot, so it draws more current and needs more install space.

Class D is the modern, efficient design — small, cool, and light on your electrical system. A decade ago class D was considered “subwoofer only,” but modern class D full-range amps sound excellent and fit behind a dash. For most installs in 2026, a class D amp is the practical choice; reserve class AB for dedicated audiophile builds where you have the space.

Watts: RMS vs peak (ignore peak)

Peak watts are a marketing number. RMS is the power an amp can deliver continuously without distorting, and it is the only number that lets you compare two amps honestly. A 50-watt RMS amp will out-perform a “1000-watt” amp that is really 25 watts RMS, every time.

When you read a spec sheet, find the RMS rating at the impedance your speakers run at. If the sheet only lists peak or “max” power with no RMS figure, treat it as a red flag about the whole product.

What to skip

Bass boost knobs, remote level controls, and flashing displays are convenience features, not performance. They are fine if included, but do not pay extra for them. Likewise, ignore power claims that are not backed by a fuse rating — an amp cannot deliver more continuous power than its fuses allow, which is a quick sanity check on inflated wattage numbers.