It's not "being tested". It's common knowledge to anyone who has spent a lot of time around amps. Nobody here is debating physics.
You
are debating physics. You are claiming that a 100-watt valve amp is equivalent to a 300-400watt solid state amp, and I am saying that is not in line with the known and observable physics behind power amplification. Just because something is
perceivably comparable does not make it necessarily so.
IE: It
isn't the wattage in a valve amp that matters. It's the impedance loading of the output transformer and the soft clipping nature of the circuit, which allows you to push a 100watt amp much much further than a mere 100watt figure implies. At full tilt many valve amps have been measured at almost double their stated output. But in such a scenario, it isn't really a 100watt amp at that point. So even that doesn't serve your concept.
The bottom line is, wattage is not a measure of volume. It is a measure of power transfer, either as a static measurement, or over time. So you cannot use wattage alone to make claims about loudness.
The reason that a 100-watt amp seems loud and a 100-watt solid state amp doesn't seem as loud, is very little to do with the wattage, and everything to do with the design. Solid state power amplifiers do not work the same way, and do not have the same relationship with the speaker.
You should be clearer in your comments, because they are misleading.
Common knowledge != knowledge
A 5-watt valve amp would seem hugely louder than a 200watt solid state power amplifier, in the right conditions.
A 50W tube amp will 'sound louder' then a 50W solid state amp, particularly with cleaner tones, as you can turn up the tube amp a lot more before detectable clipping/distortion occurs vs a solid state amp, giving the perception that it's more 'powerful' even though the wattage is the same.
Wattage is not enough information to make this claim. My point was that simply doubling the rating of the solid state amp will not necessarily get you any louder than the 50-watt solid state amp. And with a tube amp I think it is more the case that the clipping/distortion is easily detectable, but we
like it, so we don't mind going further. There are definitely points at power consumption where a valve amp starts to sound just as poor as a solid state amp can. Loadboxes help reveal this; my Diezel VH4 sounds pretty naff when the master volume is cranked. It goes extremely dark and more like a fuzz pedal than a nice cookin' amp.
Point being... in a parallel universe where humans do not like the sound of clipping or harmonic distortion, a cranked "100watt" tube head would not be desirable, so no-one would crank them, so no-one would feel the need to say things like "a 100watt valve amp is equivalent to a 200-300 solid state amp"
Also worth reminding that knob positions on different amps are not comparable. If your 100W tube amp at 4 is as loud as than a 100W solid-state amp at 9, that just means the tube amp reaches its rated output at about 4. Use a decibel meter if you want proper comparisons because we are not good at evaluating volume accurately by ear.
Yes, this is true. Which is why output is measured at wattage stages, rather than knob positions. Although humans are pretty good at evaluating volume accurately. We tend to be able to tell the difference between loudness within a 3dB window. Trained people can usually go a bit lower, at around 1 to 1.5dB window.