Impedance curves and instantaneous impedance

[Holmz]

I was reading about current source versus voltage source amplifiers and I may be a bit confused.
When we see impedance versus frequency, how  are those values determined?
Is it a steady state measurement or a swept chirp?

And then what happens for say from a pure delta Dirac type of impulse or for a step?
If the speaker has a graph the sensitivity as a function of the frequency, does the actual FFT of the speaker’s measured impulse differ from the FFT of the input voltage by exactly the same amount as the it’s sensitivity graph would show?

 

I guess it must?