Finding (calculating?) speaker and amp impedance

@asctim  Outside of exotic manufactured speakers like full-range ribbons or ESLs, I think there are a couple of reasons.

One is lack of decent tools and practice.  Old Genesis speakers sometimes showcase this.  The crossovers were "tuned" by ear and impedance be damned.  Given that a software spreadsheet had just been invented, there was not a lot of handy tools like we have now to tune a speaker's crossover for impedance, frequency response simultaneously. 

Another, and I've seen Focal do this, is that a difficult to drive speaker is seen as "discerning."  No, I'm not going over this detail, either you believe me or you do not, but reviewers give far too much positive press to a speaker that shows you the difference between an integrated and million dollar monoblock. 

Lastly, and I think the Kef is an example, is that they have a big problem with power efficiency and need a lot more current to make the design work.

@asctim Don’t assume everyone that puts their name on a product is above average intelligence.

reviewers give far too much positive press to a speaker that shows you the difference between an integrated and million dollar monoblock

+1

Every budding audiophile should endeavor to hear a time aligned [studio monitor] system with electronic XO and beaucoup watts per driver. They'd then know they were being had.

Regarding reviewers:  "and the triangle in 3rd chorus is delineated like never before" is laughable.

How to stop worrying about speaker impedance The Audiophiliac and ELAC’s speaker designer Andrew Jones set out to demystify speaker impedance.

Thank God for John Atkinson.  From my long experience in reading Stereophile technical reports it's very rare that some part of a speaker's impedance curve isn't below 4 ohms.  And vanishingly rare at 6 ohms.  Accordingly most valve amps should almost always be set to their 4 ohm tap.  If they have one.  Atkinson nearly always recommends this.  Flea power examples should really only be run into 'full' range horns with sensitivity in the high 90s and above.