Car Stereos: over amplifying a subwoofer, watt rms amplifier, watts rms

Question
I've asked a lot of supposed car audio pros this question with so many different responses that it's mind boggling. One guy today said if If my subwoofer is rated to 400 watts rms that I should get a 500-600 watt rms amp. and this way the amp runs cooler but just make sure to keep the gain control very low and no damage will occur.  Is there any validity to this????

Answer
Hi Steven,

No, I don't think there's any real merit to that idea.

Generally, I recommend an amplifier that's rated between 50 to 100% of the subwoofer's rating.  A 400-watt RMS subwoofer will work well with a 200 to 400 watt RMS amplifier.

I don't think there's really any advantage to buying more power than you need.  If the sub is rated at 400 watts RMS, there's not much point to buying a 600-watt amp, then carefully making sure it won't produce more than 400 watts.  

I suppose it's possible that the higher-powered amp will run cooler, since it will be designed to dissipate the heat produced by a 600-watt output.  I just can't see that a slightly cooler amplifier is worth the extra cost.  If the amplifiers' power ratings follow CEA-2006 standards, the smaller amp will still be able to produce a continuous 400 watts with in inaudible level of distortion.  As long as it's not heating to the point of activating the thermal protection circuit--unlikely, provided you follow the load impedance recommendations--then you're not going to hear the difference.

You'll often hear people say, "you're more likely to damage a sub from under-powering than over-powering".  This is a myth that's unfortunately very widespread, even among car audio professionals.  The fact is that the only thing that can damage a subwoofer is too much power--either driving the cone past its mechanical limits, or generating too much heat in the voice coil.

When a subwoofer manufacturer gives an RMS power rating, they're telling you the maximum RMS amplifier power rating that they recommend for use with their sub.  Choosing an amplifier with a higher rated power will only increase the possibility of damage from over-powering.

Thanks for the question!

Brian