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What size amp for a subwoofer is the question we get asked more than almost any other, and the answer starts with one number on the sub’s label.
What Size Amp for a Subwoofer? Start With RMS
Look at the sub’s RMS power rating. RMS is the power it can handle continuously. Ignore the big “peak” or “max” number printed in large type on the box, because it doesn’t tell you what the sub can really take.
A good rule is to pick an amp that makes about the same RMS power as the sub is rated for, or a little more. That gives the sub clean power with some headroom, which is better than a small amp that is pushed too hard.
Match the Impedance Too
Amp power changes with impedance. An amp might make 500 watts at 4 ohms and 800 watts at 2 ohms. So you need to check the rating at the impedance your sub will be wired to, not just the number on the front of the box.
If you aren’t sure how to get to that number, our guide on series vs parallel subwoofer wiring walks through it. You can also read about electrical impedance if you want the background.
What Size Amp for a Subwoofer: Quick Examples
| Sub RMS rating | Final impedance | Amp to look for |
|---|---|---|
| 300 watts | 4 ohms | 300 to 400 watts RMS at 4 ohms |
| 500 watts | 2 ohms | 500 to 650 watts RMS at 2 ohms |
| 1,000 watts | 1 ohm | 1,000 to 1,300 watts RMS at 1 ohm |
| Two 400 watt subs | 2 ohms | 800 to 1,000 watts RMS at 2 ohms |
Why a Little Extra Power Is Good
When you work out what size amp for a subwoofer suits you, a bit of extra power is a good thing. The amp runs relaxed. It can handle loud bass hits without clipping. Clipping is when the amp runs out of room and sends a distorted signal, and it kills subs faster than too much clean power does.
That said, don’t go wild. An amp far above the sub’s rating is easy to overdrive if you set the gain too high.
Choosing the Amp Type
So what size amp for a subwoofer setup and which type? For a single sub or a pair, a mono Class D amp is the usual choice. It’s compact, efficient and runs cooler than older designs. A 4-channel amp can work if you bridge channels, but a mono amp is built for the job and usually simpler.
Don’t Forget the Power Wire
Whatever size amp for a subwoofer you pick, big amps need big wire and a healthy electrical system. If your lights dim when the bass hits, read our post on alternator whine and look into the big 3 upgrade. A strong supply is part of getting the amp you buy to perform.
What Size Amp for a Subwoofer: Mistakes to Avoid
The biggest mistake is shopping by the peak number on the box. The next is buying an amp that is too small and cranking the gain to make up for it, which causes clipping.
Also, check that the amp is stable at your final impedance. Some amps aren’t rated to run at 1 ohm, and wiring to a load they can’t handle will make them overheat.
What Size Amp for a Subwoofer FAQ
Can I use an amp with more power than my sub is rated for?
Yes, if you set the gain properly. Too much power with a careless gain setting can damage the sub.
Is it OK to use an amp with less power than the sub?
It’s safe if you keep the volume sensible, but the sub won’t reach its potential. Watch for clipping.
Do I need a mono amp for a subwoofer?
It’s the easiest option. Many 4-channel amps can be bridged to power a sub, but mono amps are designed for low impedance loads.
How do I know the amp’s RMS rating?
Check the spec sheet for the RMS rating at your impedance, not the peak figure.
Shop Amps and Subs
If you’d like help matching an amp and sub, browse dv8shop.com or message us and we’ll point you to a good pair.
