Measuring impedance with multimeter

Recluse,

To be technically accurate, you're not measuring impedance with a multimeter. You're measuring resistance. Impedance applies to the resistance of an alternating signal. Also consider the thing you're measuring. A driver is an inductor placed inside a powerful magnetic field. Obviously it's got inductance that's going to resist higher frequencies. You're also moving wires back and forth inside a magnetic field. That generates electricity in itself that can drive impedance way up while rotating the phase angle around in weird ways depending on the mechanical properties of the driver and how it's enclosure loads it. 
Add into the mix the reactive nature of a passive crossover and there's a LOT of factors that contribute to the impedance of a functioning speaker. 
Multimeters are cheap. Audio Precision analyzers aren't. That's why. 

@recluse
Here, read this:
https://speakermakersjourney.blogspot.com/2016/12/crossover-basics-impedance.html

Speaker impedance is expressed as an average in ohms; impedance varies with frequency of input signal.

Thanks for all of the explanations and links.

For non EE types, what sort of equipment would be needed then to get a reasonably accurate measurement?

This?

https://www.vellemanstore.com/en/peak-lcr45-lcr-and-impedance-meter?gclid=EAIaIQobChMI6YXV-MP83wIVmY...

Thanks in advance

If you connect your speaker to a signal generator and run a frequency response graph for the entire audio spectrum (generally 20-20,000cps) you can see on the graph how the impedance varies quite a bit (from maybe a low point of 2ohm to a high of over 20ohm) over the frequency range. The mfgr of your speaker states it is 12ohm but that is an average of the low and high impedance shown on the graph. You should connect your speakers to the 8ohm outputs on your amplifier.