Perplexed on how single driver speakers can cover such a large Hz range

Speakers don't exactly create different frequencies and then put them together. The single signal is a complex combination created by a signal composed of all the frequencies a microphone picks up. The signal is a complex of hills and valleys one after the other all combined into one ever changing signal.

Where you really want one driver to be reproducing all frequencies is in the heart of the music---the midrange. The Eminent Technology LFT magnetic-planar driver reproduces 180Hz to 10kHz, with no crossover in that range! In the LFT-8b an 8" dynamic driver in a sealed enclosure does 180Hz down, a ribbon tweeter 10kHz up.

My 2 cents:

- Most speakers under $2k have junk crossovers, resonant cabinets and mismatched drivers. You're losing a lot of detail in the midrange and you don't even know it. It's only clear after you listen to a decent pair of single driver speakers. 

- Most speakers with the exception of true "full-range" towers don't extend past 50Hz. So the whole "fullrange drivers can't do bass" argument is so ignorant to the fact that most speakers use midrange drivers for bass. Most speakers benefit from a sub. Nobody is going to convince me that Harbeth P3SR or KEF LS50 have deep bass. 

- If you live in a reasonably sized flat you're not going to push the volume to night club levels. My guests often complained that the music was too loud on my small single driver speakers. But the same could be said about a large Bluetooth speaker. How much volume do you need? 

These factors have convinced me to buy the Closer Acoustics OGY blind and I have no regrets. Just find me a better (new) speaker under $2k. The midrange, treble and imaging is step up from the KEF LS50 Meta. The bass is fast and punchy thanks to the transmission line. But don't expect deep full-bodied bass. You can get that from a subwoofer. 

I'm also surprised by the enthusiasm surrounding coaxial drivers which exhibit a lot of the same problems as single driver speakers: doppler effect, weaker bass due to smaller speaker excursion (the woofer cone acts as a horn, a moving horn is problematic). And on top of that, coaxial drivers have crossovers and the multiple drivers aren't moving at the same speed causing a time delay. 

+1 as usual to Atmasphere for an eloquent explanation.

@kokakolia, with respect, I think you are conflating/confusing perceived loudness and frequency range. A speaker with limited frequency range will often be perceived to be louder than a full range speaker especially if it's frequency response is ragged. A downside of speakers with limited bass response is that they are often driven harder in an attempt to get some bass impact, which then results in them being played too loud and showing up deficiencies elsewhere in the speaker.

It is the reason why the best headphone and the only one i like is a Hybrid with a dynamic cell specialized in bass and a electrostatic cell specialized in higher frequencies over 4,000 hertz the cross over slowly decreasing point for the two cells..And a grid of Helmholtz tuned resonators inside to clean bass and mid bass... it work so much well that none of my past 9 headphones compared one second to the K340... All are under my bed for eternity or for computer use... 😊

The AKG K340 can make a soundfield more defined and clearer than my speakers because of what atmasphere explained so well...

My room dedicated acoustic so well it was tuned , was limited by my Mission Cyrus speakers under 50 hertz...And their tweeter limitation and roll off..

When i lost my dedicated room i was sad... When i optimized this headphone i enter in sonic heaven anew but with no more too much acoustic limitations... A well optimized modified AKG K340 rival any headphone today... It is the only successful  hybrid headphone where one of the cell is not only a super tweeter as the dharma was..

Any designer in audio is an artist not only a scientist... because he must work and jugg with many trade-off at the same times... The designers who are not artist are not the great one , they apply a recipe...