Speaker sensitivity, impedance, and calculating amp power


This is an elementary question, but I'm not quite understanding how to match amp power to speakers. When I searched around on this forum, I found many discussions which went deep into the weeds. I am hoping for a way of calculating the level of amplifier power I need for speakers with different sensitivities and impedances.

If you have the patience, here's the basic question. So, I've learned that one must consider a number of factors to calculate the amount of amplifier power to drive the speaker:

Sensitivity of the loudspeaker
Loss of db at the listening position
SPL desired at listening position
Amount of headroom desired

Most discussion of the demands a speaker will make on an amp focus on the speaker sensitivity. But the speakers I'm considering vary also in their impedance. How would I use both of those factors to estimate necessary amplifier power to drive them with a comfortable amount of headroom?


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I'll go buy the Harley book. I'll try to consult it before asking questions like this. I assumed there were no prereq's for asking a question.
@millercarbon — I'm interested in both. It starts with a practical question but leads into theoretical ones, which I want to get a handle on. I'm not seeking to ask questions with hidden motives. No need to out me.
@erik I'll reconsider my question. 

Another way to have asked the question would have been:

"What role does impedance have, if any, alongside other factors in the calculation of how much power should be used to drive a speaker comfortably?"

@tomic601 How loud? SPL of about 80 db, which I would assume with classical/jazz would have peaks of about 100 SPL?

I have been using various calculators to try to see how all the factors I mentioned in the OP vary. For example, there's this one from Crown: www.crownaudio.com/en-US/tools/calculators#amp_power_required
And a nice sheet linked to here on the Hans Beekhuyzen Channel www.youtube.com/watch?v=itKqSWH07_Y

The reason I asked the question was because the calculators I found do not mention the impedance of the speakers. Again, I'll reconsider my question based on what Erik said and what the Harley book says. If I could delete the question, I would.

Post removed 
+ the Harley book. Should have been mentioned in all of the OP's current threads. I myself should have done so.