Designs with coaxial drivers;

Use of use of two identical/similar drivers;

Adding sub-woofers.

Heck, I even cringe at including drivers that use of whizzer cones.

IMO there aren't many actual single driver speakers because of a lack of true full range drivers (most are mid/tweeters even if they're 8 inches across).

In many places folks delude themselves into believing that response somewhat flat to down around 50 Hz makes for a full range speaker.

I applaud everyone here for striving for realistic bass. OTOH if we really held to the single driver premise there would be little to discuss here. To get back on track, lets list all known single driver speakers with full/realistic bass (with a somewhat loose definition of "full bass").

But by all means let the premise serve the music, in other words if push comes to shove full range music should not be sacrificed to serve the ideal.