How To Measure "Current" In An Amplifier?

^Perhaps I should rephrase the question:
What does feedback have to do with linear powerput into varying impedances and accompanying variable sensitivity?

@unsound

With very high output impedance the frequency response of the amplifier looks like the speaker impedance. I.e. not flat! :)

With very low output impedance the frequency response of the amplifier stays flat.

The missing step:

Increasing feedback reduces the amplifier output impedance. That and lowering distortion are why most amplifiers have at least some feedback incorporated into the design.

@unsound

Take a look at the top chart from Stereophile:

http://www.stereophile.com/content/conrad-johnson-lp125m-monoblock-power-amplifier-measurements#ETgE...

Notice the squiggly black line (called grey in the text)? That’s what happens when an amp with high output impedance drives the varying load a speaker presents. The frequency response of the amplifier goes up where the impedance of the speaker goes up, and down where the speaker impedance goes down.

Compare this to an amplifier with very low output impedance:

http://www.stereophile.com/content/theta-digital-prometheus-monoblock-power-amplifier-measurements#Z...

There is still some variability, but it's MUCH less than +- 1dB. :)

Mind you, I make NO claims one amp is better than the other. :) This is a pure specmanship so far. I am not sure given the chance to own either which I would prefer.

Best,


Erik

Erik, I wasn't quoting you saying High DF was bad, only referring to Almarg's response that a high DF would wreak havoc on tube amps.
Though if you could elaborate why, I would appreciate it.
Thanks for your replies, but I am still a bit confused.
Ohms, watts, and voltage, I get, but this Damping factor still kind of eludes me.

OK, but even with that feedback, unlike many ss amps, the vast majority of tube amps can't double down/halve up with varying speaker impedance and the corresponding varying sensitivity, and I would assume therein deviate from linear frequency response and ergo(?) distort timber, no?