Single driver vs traditional 3 way loudspeakers

Full range single drivers do have their following.  That being said, it's incredibly difficult to engineer a single driver that will do a wide range (from low 50 Hz all the way up to high 20 kHz).  Some can do this, but with compromises.  I think the Mark Audio paper drivers are some of the most natural sounding full range, but they don't have good low bass response and the highs are soft and rolled off.

I've listened to several full range driver speakers and all have compromises.  Either they are soft, or lack bass, or have whizzer cone artifacts.  The Cube Audio Nenuphar look interesting with a 10" woofer and 3 whizzers.  I have not heard them directly, but youtube videos seem to reveal the typical whizzer cone effect.  It's a type of echo or resonance or shouty effect.  It's not perfect and is not going to be as transparent or clean as a traditional tweeter, but it provides a single driver full range scenario.

The Seas Exotic 8 is another possibly decent full range solution.

Single fullrange speakers suffer from bad distortion in the highs because the cones are not high quality enough to do high frequencies. You would never use a 4 inch dome as a tweeter in a 2 way speaker would you? Most tweeters are one inch. They need to be small and light to work well. Secondly small fullrange speakers cant do bass. Not just 50hz but even 150hz. 

What you need is at least two drivers. Each handles one half of the frequency range. A crossover device is then used to split the signal in half. 

Speaker design is not rocket science.  

@grinnell    Single driver crossover less design assuming no any  coil or capacitor involve, for 2 way like monitor DE Capo   the woofer may connect direct with no crossover network, but tweeter using capacitor that meaning first order crossover design involve  for tweeter only, They must using capacitor to avoid blow up tweeter .   Most of 2 way design using one High quality coil ( Inductor   ) for woofer also to  get off cone break 
frequency. If De Capo dont using any coil i dont know is good or no .
@auxinput   Agree for 100 % , in all my design i am simply remove whizzer cones 

@kenjit  agree, how whizzer cone , just piece of paper can be compare with High quality tweeters , This is Woo do. Basically whizzes cone   drivers was used  in all analog Tube amps and Pro acoustic in Cinema
How they widely used in High End is magic 

I’ve listened to several full range driver speakers and all have compromises. Either they are soft, or lack bass, or have whizzer cone artifacts. The Cube Audio Nenuphar look interesting with a 10" woofer and 3 whizzers.

PHY has introduced a 6" driver that has no whizzer cone and yet is extended and smooth at high frequencies. Its hard to get it to go below about 60-70 Hz, but at that point you can use a sub with it quite successfully. I recommend keeping the deep bass out of that driver- to make the highs right it has a very lightweight voice coil that simply does not handle a lot of power. But it is 96dB at 1 watt, so you don’t need a lot of power to make it work in most rooms.