There are really TWO entirely different questions here; but everybody seems to conflate the two....
The first question is: "Can two amplifiers that measure the same sound different?"
The answer to this question is easy: unless you believe in magic, then the answer is "No".
Now we come to the second question (which is sort of obvious now that we've answered the first one):
"How is it that amplifiers DO sound different, often even when they seem to measure the same?"
The answer to this question is obvious as well: "Apparently we are NOT measuring all the parameters that affect the way an amplifier sounds."
Now, THIS answer leads us to a NEW question:
"What aren't we measuring that, since it affects audio quality, we SHOULD be measuring?"
What I'm trying to avoid here is the tendency, which seems prevalent these days, to throw up one's hands and say things like: "Since amplifiers that measure the same can sound different, then there's no point in doing measurements." Not only does this conclusion lead to muddy thinking, but it makes things even more difficult than they already are. It also makes it almost impossible for people looking to buy an amplifier to make informed decisions in today's market (where you rarely get to listen to something before you buy it). Fortunately, it's also true that, from an engineering point of view, while the relationships between various factors aren't "dead simple", they also DO still make sense.... if you take the time to learn the details.
Take distortion, for example....
Different types of distortion do indeed sound different; no surprise there. We are all pretty well aware, for example, that second harmonic distortion often lends "body and warmth" to the way something sounds. It makes voices sound "fuller and smoother". In contrast, third (and higher) harmonics can often make things sound "harsh" or "nasty". Therefore, it makes sense to say that, IF THERE IS AUDIBLE DISTORTION, then it is preferable (to most people) if that distortion has more lower harmonics than higher ones. This is something that you can measure easily enough, but most simple "THD=%" specs don't do. Now, I think we can all agree that there is SOME point below which ANY distortion will be inaudible (we may not agree about what % that is, or whether it is the same for different harmonics, or at different frequencies). From these two statements, we can infer that, IF THE LEVEL OF DISTORTIONS OF ALL TYPES IS BELOW AUDIBILITY, then we won't hear a difference between them. (All I said was "if you can't hear two different things, then you can't possibly hear the difference BETWEEN them"). We are also left with the possibility that some people might actually PREFER audible levels of second harmonic distortion. (It is well known that vacuum tube amplifiers produce audible levels of lower harmonics - especially the second harmonic.) In fact, it's pretty obvious that, if one amp sounds different than another, then there is SOME audible (and measurable) difference between them. (After all, if the AUDIBLE DIFFERENCE isn't produced by magic, then it must be something real - and so it is also measurable.)
See, it's not mystical at all.....
We should expect amplifiers with super-low levels of THD to sound similar (in that regard).
(They may still sound different for OTHER reasons.)
We should also expect amplifiers with higher levels of distortion to sound different; and, furthermore, we would probably expect that, in situations where audible levels of distortion do exist, most people will prefer the equipment that produces more lower order harmonics and less higher order harmonics.
These seem to correlate pretty well with the way products sound (to me), and how they generally get rated.
Actually, I've carefully avoided one last factor there..... it's called "perception bias" (or "placebo effect" or "expectation bias").
And THAT is a modern technical term that accounts for most of what used to be called "magic".....
In short, what we THINK we hear can be influenced by what we EXPECT to hear.....
(This is why double-blind testing - if you do it right - is important; because, by keeping us "in the dark", it prevents us from having any knowledge or expectations about what we're listening to in advance, so we can base our perceptions of what we hear SOLELY on what we are actually hearing. )
See, numbers DO work - if you use the right ones.....
Back to the question, though.....
Audio companies are in business to sell audio equipment.... well, duh!
So, yes, it is a conspiracy of sorts.....
Do we (companies) try and explain all this, and risk offending some non-technical customers, by saying things like:
"Tube amplifiers sound different because they make audible distortion, which happens to be the second harmonic kind that many people find pleasing, and because they have very low damping factors, so they sound wildly different with different speakers, or even different speaker wires"?
Or do we just take the easy route and say: "We make em'; the sound wunnnderfullll; if you like the way they sound, ignore the science and buy them; don't listen to all those silly people with their annoying measurements"?
Or do we even take that next step and say, in effect, "it really is magic and you should trust us because we're magicians"?
And does it make any sense at all for us to remind you that, if you're like most humans, then by simple human nature,
you WILL be inclined to think that the most impressive looking amplifier or the most expensive wire sounds better - even if they're really the same?
And the answer to THOSE questions depends on whether we want to sell you equipment by any means possible,
or whether we prefer to make sure you get the equipment that will actually sound the best, without paying for magic or phony science, and get it at a price you can actually afford.
(Here at Emotiva, we find that being honest makes it easier for us to sleep at night ....)
Originally Posted by A9X-308
But it's trivially easy to get better than 100dB SNR and THD and has been for a couple of decades so whilst you can easily measure the difference, audible artifacts in typical use from these effects is not going to be a differentiator between two amplifiers.