How much power needed to drive 91db speakers?


Sonus Farber lists the sensitivity of my speakers at 91 db SPL@ 1 meter @4 ohms.  They also say I should use  50-450 watts of power. My PS Audio amps pump out 500 watts @4ohms, so the max isn’t a problem, but if I switched to something 15-50 class A watts, would that be more than enough power?  
 

Thanks in advance.

curiousjim

I would like to thank everyone except @billstevenson for giving me intelligent and helpful answers.  I’m going to borrow a friend’s DVR that even though it class D, it’s rated at @75 watts per channel, so I should be able to get an idea.

If your going to check out a class D amplifer, you may wish to consider the Hypex Nilai 500.... Great reviews :-)

An amplifier power in Watts is not an absolute measure of power. A standard example, 50 watts in a tube amp can be equivalent to double of Watts in a solid state amplifier. My 5 Watts SET amplifier drives surprisingly good my 87 DB speakers, my normal listening level is less than 20 % of max volume. If you want a guaranteed outcome with a 50 Watts amplifier with your speakers choose a tube amplifier.