Determining actual impedance

OK there are surely some question (s) at least in my mind, surrounding the actual or even the nominal impedance of speakers.

I've personally been told by some speaker makers that they measure impedance in ways other than how the rest of the crowd measures them. Which lead me to believe, "If they don't follow the norms, how many others divorce themselves from stand measurements?"

What do I need to do in order to find out the working impedance of a speaker?

It would seem to me that there is some way to find out just what a speakers imp will be under load at home.

Reasonably simply. Rather than finding out after much expense in acquiring and integrating a pair of them into one's system... or trying to find an appropriate amp (s) suitable to them.

Even finding out the static numbers would be a start... or at just a few pre-determined frequencies.... or at their lowest ebb.

I'm thinking this info to be most valuable.

Is it? Well then, only 'how' to do it remains?

My sincere thanks to all who participate.