Being at an auction (raising a hand)
What I find so inexplicable about the switch over test is this ....
Originally Posted by Euler
The relay change-over box has an LED which glows when the relays are connecting amp A to the speakers and extinguishes when amp B is connected. In my (limited) experience over the years with this switch-over if it were not for the LED glowing or not (and possibly the smallest of audible clicks) there would be no way of knowing that a switch-over had actually occurred.
Indeed, to be extremely generous to the test subject (and I am under no obligation to do so, but am compelled by fairness) I would allow the tester complete control over when and for how long he wished to switch between A and B. He could switch as many times as he liked. Thousands if he had the enthusiasm. His response, identifying the model 'A' or 'B' would be recorded against the LED on/off status by the adjudicator.
If I was less generous I'd construct the test like this: the LED would be removed from the switch-over box and extended on long wires to be only visible by the adjudicator. The adjudicator would be in command of the foot switch. Without warning and randomly, the adjudicator would operate the relays but would give no clue to the test subject that he had done so. The tester would be instructed that if at any time during the test he heard what he believed was a difference in sound he was to raise his hand. The adjudicator would operate the change-over 100 times and each time look to see if the test subject raised his hand. If at the instant of change-over the tester raised his hand, meaning he had heard a difference in sound attributable to the amplifier switch, that would be recorded as a positive result for him*.
I'm fairly confident that there would be negligible correlation between the actual change-over and the hand raise. In fact, I'd fully expect the hand to be raised and fall when the same amplifier was driving the speakers continuously, triggered solely by some internal process in the human brain.
This is a purely psychoacoustic matter. It is precisely the sort of human observational experiment that reveals just how unreliable our senses are. To deny that, or to fight against it is just silly. We are the product of evolution - this is just the way we are built.
My main thrust is, as I have stated unequivocally: there are far better reasons for choosing one amplifier over another than 'sound quality'. Durability, styling, features to name three.
*I would expect that unless the amplifiers are wildly different in performance (or one exhibits a loud click) he (and that includes me) would achieve 10% success rate identifying the instant of switch-over.
Alan A. Shaw
Harbeth Audio UK