Match the RMS power of the subwoofer to the RMS power of the amp?

Question

Im confused!

So. basically you want to get an an amp that has about the same RMS power as the woofer?

Lets say the woofer is 400watt rms power 800max

You will need an amp that sends out 400rms power and not more?

Answer 1

I would say an amp with RMS power equal to 20% of the handling capability of the speaker you are driving is about right.

IE: 40w RMS amp for a 200W Speaker.

Have a look at the specs of the speaker carefully (and the amp too). You will find the 200w speaker usually can only handle 30-50w constantly, and a 200w peak for a split second.

Amps (cheap ones) always over-state their RMS outputs too.  600w (4 x 150w) may well be 4 x 20w. Their 600w was achieved for a millisecond at 50% distortion.

Note that when I said "40w RMS amp for 200w Speaker" you are only getting 40w RMS at full volume on the head unit (and hence max distortion probably as well).

A good 200W RMS (2 x 100w) amp will drive 2 x 800W subs quite well.

Answer 2

First of all, ignore any "max" power ratings, both on the amps and the subwoofers.  They have no purpose except to add more confusion.

Ideally, you'd want the RMS rating of the amplifier to be the same as the sub's RMS rating.   You can use a much lower power amp without a problem; subwoofers aren't damaged by under-powering.  You can use a slightly higher powered amp, but you'll need to be more careful.

With your 400-watt RMS sub, you can use anything from a 50-watt to 450 watt RMS amplifier.

Be sure to match the impedance ratings of the sub and the amp.  Most amps produce more power at 2 ohms than at 4 ohms, so if you have a 4 ohm subwoofer, make sure you're looking at the right power rating.  Also, make sure that the amplifier's power rating is CEA-2006 compliant.  This means that the power rating method conforms to a universal standard, so you don't have to worry that it's over-rated.