The under appreciated impedance curve

The quick answer: The weaker the amp, the more its output in the frequency domain will look like the impedance curve.

And for those who want to know, here is the proof of that, with a well known push pull tube into the Stereophile simulated Kantor speaker load (which is a moderate easy load)

Simulated Kantor load (solid black wavy line)
https://www.stereophile.com/images/archivesart/scan58.jpg

Push pull tube 4ohm tap frequency response (+ - 5dB!!)  into that same Kantor simulated load (solid black wavy line)
https://www.audiofast.pl/assets/Uploads/pict2-prima-rec.jpg

See the amps frequency response take a dive at 30hz, 200hz and 4.5khz (more of a tone control than a ruler flat response)
Now look at the Kantor loading at 30hz, 200hz and 4.5khz, see how the load dictates what the response of the amp is doing at the same frequencies??? No wonder they sound coloured!!!

Cheers George

The under appreciated impedance curve

Under appreciated?? I don’t think so, to those that find/look and know how to use it.

I believe "it" together with the combined "-phase angle" curve (EPDR) if hard to drive, "becomes the no1 criteria" to selecting the right amp to get the very best from that particular speaker. Probably that’s why it’s the 1st thing John Atkinson measures in Stereophile.

Cheers George

I do think that the community at large does not appreciate how much we can learn.

I second that.

That doesn't mean to be an accusation of anyone in particular.

More more it's talked about, the more they'll make a effort to at least try understand them.

For those how wish to understand impedance/-phase graphs using Ken Kantor's easy simulated speaker loading. 
  
https://www.stereophile.com/reference/60/index.html

https://www.stereophile.com/content/measuring-loudspeakers-part-one-page-6

Cheers George