[Radio Wrangler]

It's how the turns ratio of output transformers are calculated.

Of course, the impedance of real loudspeakers wanders all over the place and spoils all your nice calculations, but you have to try.

With transistor amplifiers, negative feedback is used to control distortion and to allow direct coupling of stages without creating DC problems, the feedback reduces the output impedance until the circuit becomes virtually an ideal voltage generator, and so quite tolerant of load impedances.

Simple circuits with valves have little or no feedback and load Z becomes much more important because it sets the load line directly.

David

David