Good speakers less efficient?

The efficiency and impedance of the most popular dynamic speakers solely depend on Faraday's Law i.e. on the driver itself.

The impedance of the coil rises with the freequency growth
Z=wL
For DC current the coil impedance is zero(w=0)or same may apply for freequencies close to zero.
In order to reproduce lower freequencies the coil should be quite massive to hold a large current hence the impedance of such will drop. Hence the full range speakers require powerfull amplification with good current drive.

Larger drivers can reach higher SPL with smaller current and smaller amplification hence more efficient.

Small drivers need larger amplification power to move the air hence less efficient. The advantage of the small driver full range speakers (Dynaudio,Totem) is WAF, compact soundstage and imaging.

I agree most mid to large size speakers suck most amps dry.
I just looked at the Tyler Linbrook Signature System, a WMTMW design. Ty rates it at 4 ohms/92 db. I demoed my small Jadis OR with them and had no trouble at all.
Which testifies to the super high quality of trans on the Jadis and the fact that Ty knows how to design a crossover to make this impressive and imposing speaker work fine with a 40 watt tube amp. Classical Orchestra sounded rich and beautiful sound sound stage.
Good point for a topic.
Big deal the speaker is large and full range. What sort of power requirements does it need?

Thank you all for your responses. I now have a better high level understanding of the design issues and tradoffs.

My experience has been that high efficiency speakers are more likely to compress than low efficiency speakers...even at modest SPL levels. A low efficiency speaker often remains more balanced at various SPL levels whereas a high efficiency design often sounds balanced only within a much narrower SPL range.

I don't know why this is....but it is certainly my general observation...perhaps Duke can explain? (I am referring to regular box speakers here)

dipolar radiators have efficiencies in the 85 to 88db range.

i happen to prefer this type of speaker. depending upon the room and the impedance curve, they can pose a challenge fot a tube amplifier.

if one prefers this design to other designs... well, draw your own conclusion.