High-Efficiency Single Driver Speaker System

You might also try posting your question over in the cube audio thread...  https://forum.audiogon.com/discussions/cube-audio-nenuphar-single-driver-speaker-10-inch-tqwt-enclos...

 Designing a single-driver speaker is very difficult since that driver needs to cover the entire frequency band. i stating that one problem with such speakers is that they perform poorly at the frequency spectrum’s upper and lower ends.   My company Bacheaudio  further stated that he tried adding a tweeter to his early speaker models, but got poor top-end results. we also tried pairing the speakers with subwoofers, but found that a suck out in the upper bass to middle-midrange region of about 100 to 500Hz caused voices and instruments such as piano and cello to sound thin.

 

What Bache audio ultimately gravitated towards was the so-called “augmented wide-band” (AWB) speaker, which uses a single wide-band driver that covers a large portion of the audible frequency band accompanied by several of what he calls “helper” drivers, in this case a super tweeter and one or more woofers. we states that this hybrid design incorporates the best attributes of the one-way designs (exceptional dynamics and coherence) and their three-way counterparts (excellent frequency extension and dispersion characteristics and the ability to play loudly without distorting).

 

There are lots of full range speakers with high efficiency. 90-100.

I don't think there is a "single" speaker with that capability. But there are certainly coaxial two way speakers out there. GPA, Great Plains Audio, has upgraded versions of the Altec 604. Tannoy is still in business. Probably others too.

I do like high efficiency speakers. Mine are not coaxial.

I do have one low efficiency pair of speakers.