Amplifier specs, does they matter?

Sorry for my lame typo!

So, designs that boast low THD through the use of negative feedback are likely to sound bright and harsh. And yet some amplifiers are being praised as having ultra low distortion through the use of extensive negative feedback.

A spec showing that power doubles as the impedance drops from 8 to 4 and then from 4 to 2 may be misleading. I recall a Stereophile test report a few years back of some high-powered solid-state amp, perhaps a Classe, whose ratings indicated just such a doubling. However, the measured power output turned out to be considerably greater at 8 ohms than the rated power, slightly greater than the rating for 4 ohms, and it just barely made the 2 ohm rating. It seemed clear the manufacturer was playing a game with the specs. It had intentionally downplayed the actual output at 8 ohms just to give the appearance of doubling its power for 8/4/2 ohms.

Nope......... in another vein..anything can be justified with statistics.

Psaq, In normal test for THD amplifier is fed with pure sinewave ant tested at the output for anything else present. Not only that this test says nothing about THD when driving your speaker but also won't show any high order harmonics manufactured by deep negative feedback in Transient Intermodulation.

40dB of negative feedback means that amp was designed with 100x higher gain that is reduced back to normal by feeding output signal to the input in opposite phase (cancelling 99% of the input signal). This scheme is wonderful and improves everything 100 fold, but when rapidly changing signal (music) is applied amplifier for a moment has higher gain (because of input/output delay) and output overshoots (signal fed back to the input is too late). It can be easily shown when testing amplifier with square wave. This overshoot translates into unpleasant high order odd harmonics. Such amp will have fantastic THD, IMD, DF etc. specifications but it will sound horrible - guaranteed. Even power ratings can be very misleading. Because of all that I think that specifications are pretty much garbage. I would use them only, as Al stated, to exclude certain amps that, for instance, cannot drive my speakers etc.

^^That.