And really, Quad have developed their amps w/o any listening at all with different speakers - sry. such claim warrants proof.
The definitive web reference to the original Quad ESL
An interview well worth reading, but here is a snippet:
TAA: Have you any opinions you'd share on the relative merits of distortion tests, such as harmonic, two-tone IM, transient IM, or slew rate limiting, as clues to amplifier quality?
PW: An amplifier should, within its limits of voltage mid rate of change of voltage, (which is slew rate limiting) if you keep within those two it should be very, much better than any program material. These are the things that are measured at .01 per cent or .05 per cent. But what is listened to is usually a program with 2 or 3 per cent distortion in the first place, 1 hat's the least you call get on records, tapes, and such things. Listening tests are usually not done in this region of .01 percent distortion. I'm quite convinced within that range the amplifier is just as perfect as you like to make it. It's quite possible to put 50 amplifiers in cascade, each one into aloud, potted down into the next one, and to listen to the 50th one or to linen to the first one, and the sound will be virtually the same. So I think you call make an amplifier just as good as you like, and no more different than a piece of wire. But where they vain, when these tests are done, are a whole lot of areas. T o start with, you can compare one amplifier with a bass cut-off of 20 Hz and another one that goes right down to DC. It you've got a program with a bit of fluffing going on at 5 Hz Or so, the speaker cone in one case will be moving, and in the other case it won't be moving. so the sound from the speaker will be different. This isn't really a condemnation of the amplifier, it's that they Shouldn't have a this 5 Hz stuff there in the first place. So if you compare an amplifier with a straight wire, you've really got to make the straight wire have the same bandwidth as the amplifier, and the same terminating impedance as the amplifier. Once you do all these things, then the amps will be just as good as the straight wire. The peripheral effects are what get people into trouble. You can see why you find these differences in amplifiers. You can always find them. If people test two amplifiers and say, "These sound different" there's no magic in it. Spend two days. maybe a whole week in the lab, and you find out exactly why they're different and you can write the whole thing down in purely practical, physical terms. T his is why these two sound different, and the cause is usually peripheral effects. It is not really a case of good or bad amplifiers, it's that tile termination impedances are wrong. or something of that sort.
TAA: How do you rate the merits of listening tests to instrument tests?
PW: We designed our valve (tube) amplifier, manufactured it, and put it on the market. and never actually listened to it. In fact, the same applies to the 303 and tile 405.
People say, "Well that's disgusting, you ought to leave listened to it." However, we do a certain amount of listening tests, but they arc for specific things. We listen to the differential distortion - does a certain thing matte' You've got to have a listening test to sort out whether it matters. You've got to do tests to sort out whether rumble is likely to overload pickup inputs, or whether the high frequency stuff coming out of the pickup due to record scratch is going to disturb the control unit But we aren't sitting down listening to Beethoven's Fifth and saying "l hat amplifier sounds better. let's change a resistor or two. Oh yes, that's now better still." We never sit down and listen to a music record through an amplifier in the design stage. We listen to funny noises, funny distortions, and see whether these things are going to matter. to get a subjective assessment. But we don't actually listen to program material at all.