I don't know how to do those calculations but I can say I have never been unable to find that information by just using Google or an email to the manufacturer. Not the answer you were looking got but maybe helpful?
Finding (calculating?) speaker and amp impedance
I'm starting to understand why speakers with high efficiency and perhaps more importantly a flat impedance curve work well with tube amps.
If not published by the vendor/manufacturer, is there a way to determine the impedance curve from the specs that are provided?
Also, I have a pair of Magnepans that need high current amplification.
Is there a way to determine the current of an amplifier from vendor/manufacturer provided specs?
Thanks everyone!