Power output of tube amps compared to solid states

Atmasphere.

No further clarification needed on my behalf. Transients are key. Its pretty clear to me that its mostly about details relating to distortion and how different factors contribute to that, as you say.

I am going to jump into this "tower of babel" with all four feet and state my qualifications for doing so.
Before I became an Audiophile, I was an electronics technician who knew all the electronics formulas. "If you can not measure it, you can not hear it" was my slogan.
After I became an Audiophile, I laid my meters to rest. I can hear things that no meter can measure.
"Is this dog better than that dog"? Unfortunately, no one can answer this question but you. This is not a scientific arena, this is a very subjective audio arena.

I have to believe science plays a role here, there is still good design and bad design and I believe is governed by understanding electrical principles. If that is not sound, no pun intended, you are not going to get good equipment. Now as to the seasoning that a knowing chef wishes to use, that is more subjective, and the art in audio engineering IMHO.

I think it is useful to differentiate between matters of opinion and matters that do involve empirical differences but differences that we may not currently be able to accurately measure.

We do not currently measure amplifiers playing actual music and so do not really look at harmonic, IM, and other types of distortion products amplifiers actually produce making *music*. Furthermore, and much more importantly, we know only a very little bit of how to "weight" the results because we know rather little about how the ear/brain system actually works - what sorts of distortions make music unpleasant or unrealistic and what sorts really just don't matter all that much. (Of course we do know some of that, as Atmasphere & others have mentioned.)

Why some audio amplifier designs tend to sound better or more realistic may not be easy to describe empirically but it is at least not entirely a matter of opinion. Preference for dogs is. :)

(Ok, if you establish certain criteria, such a strength or cuteness, one could of course rate dogs quantitatively as well...)

I found very interesting work that was done by a group of Russians a while back. I am pretty sure I printed it out but I originally found it online. I'll have to see if I can find it again to post a link to it here, but at any rate, they had actually done measurement studies of how different amplifiers amplify Gaussian white noise (much closer to music than a sine wave is). I believe they may have also used music too.

They did Fourier analysis of the outputs of each amplifier and compared them. They found very real differences in the low-frequency reproduction, not much difference in the midrange, and once again some differences in the treble. Then they repeated the tests using the "best" amp of the group with various cables hooked up to its output. I think they used like 10 meter long cables to magnify the effects. Once again, the responses were different with different cables.

I'll see if i can find it again. Last time I looked for it I wasn't able to. But I found it extremely interesting and have not seen anything like it since. Maybe I'll just take some amps to the lab and redo the experiments myself! That's what I should do if I can find the time.

*PS* I just did a search to see if I could find it and ran across this paper. I haven't read it yet but it looks interesting. Too bad the input signals are still sine waves though....

www.apiguide.net/04actu/04musik/AES-cableInteractions.pdf

Arthur