How much amplifier power do you really need?

[RebelMan]

@RebelMan

The points you quoted from Roger Sanders' white paper are his conclusions, not assumptions.

They follow pretty much from this simple maths:

Let's say you need around 5 W RMS to achieve normal listening levels (whatever they are) with a low-ish efficiency speaker in a normal-sized room.  Given that -- from unbiased sources -- we know some music can have a crest factor of over 20 dB, that means the amplifier has to deliver over 500 W peak power to reproduce that music without clipping.

That seems very straightforward and uncontroversial to me.  Which of the two premises do you disagree with, or what is the fault in the logic?

Actually, it is an assumption Roger is making and I will explain. 

I quoted him directly from his paper so I don't see how you saw a conclusion at that point early in his paper.  It looks to me like you extrapolated what he is saying to make your math work around what he is saying and I do agree with your math.  However, I have never seen 20dB crests at anytime in my many years in this hobby.  I have seen 10+dB but that is not to say that maybe someone somewhere has actually seen crests go that high.  It seems to me it was most likely an exaggeration.  In any case, using your figures a 500W draw doesn't say much and this is where the assumption comes in.  He does not say anything about the load.  Have you ever seen an impedance-phase curve?  If Roger superimposed such a curve over the power curve then he would have some good news.  He didn't.

I bet my little 140 could muster 500W on it's way down to 1 ohm.  That 4KVA power supply it has makes it a BEAST.