How much power needed to drive 91db speakers?

@curiousjim. Speaker power requirements see here. 

Mike

The answer is in your room size and how loudly you listen along with the impedance curve of the speakers.  In a 14 x 20 room with a 90dB SPL monitor I use 55w of class a tube power and they are driven well.  25w from a SET mono I have is adequate in the same space.  In my 20 x 40 main basement, neither is adequate at reference levels. 

My speakers also have a nominal 6ohm impedance.  Usually speakers measures at 4ohms are less sensitive than the measured spec due strictly to the way it is calculated.  See any review for Tekton in Stereophile.  It is in how the math is done.  

so the answer is maybe, possibly probably but need to know more.  

• My input on the output required.

Simple logic….. l am not an engineer but time has taught me a few things which l put on offer and share here.

1. Just make sure your amplifier is not having to work flat out to drive your speakers.
2. Some people may think their amplifiers are matched just because their speakers go loud.
3. Remember 4 ohm and 6 ohm speakers draw more watts per channel power than 8 ohm

Amplifiers must have a reservoir of extra power to draw on for when the music demands. Underpowered and there will be clipping, distortion and in extreme circumstance’s the amplifier unable to control the drivers. Sometimes the cones can get torn or distorted and written off when an amplifier looses control.

In simple terms a mismatched amplifier will overheat and possibly fail, (if no protection circuits) and could ruin your speakers.

A comparison would be equivalent to putting an English Mini engine into a racing car. It would work fine at first but inevitably burn itself out.

Simple facts but as true today as when l started with hi-fi back in the 1960s.

@kofibaffour 

I said class A watts.  I never mentioned Tubes.  But now that you mention it,  there’s an ARC 80S amplifier listed elsewhere that peaked my curiosity.😁 It uses 4KT 150’s and can put out 70 watts. 

ARC Ref 80S + Sonus Faber is an excellent match.