@gs5556 How right you are!
'Nominal impedence' is generally concocted by a speaker manufacturer to hide elements of his speaker's impedence curve that he would rather hide. It has no basis whatsoever in physics. Responsible manufacturers show the full curve for impedence vs. frequency and the phase angle at audio frequencies, because bad combinations of impedence and phase angle can often occur making a speaker tougher to drive than could be apprehended from the impedance curve alone.
Incidentally I have never seen a speaker whose impedence measures a flat 2.5-3 ohms over 100-10k Hz. Have you?
This poor manufacturer behaviour is mirrored by not quoting a dB range when specifying low frequency extension, and by over-stating sensitivity, which occurs very often.
(Proper) measurements matter.