One of the leading proponents of a single full range speaker element with no crossover are Pearl Acoustics and Mark Audio. Both keep the driver fairly small to preserve some high frequency dispersion and so give up deepest bass extension.
Fritz, Totem, and maybe others have made 2-ways with "capacitorless series crossovers" to closely approach the ideal of a full range driver without the loss of high frequency extension and dispersion.
The EPI 100 and all its siblings used a single cap to attenuate lows to the inverted 1" paper dome...couldn't be simpler!
The Walsh driver found in the Ohm A, F, and more recently German Physics' DDD driver, which to my knowledge use no crossover components, yet achieve full range and omnidirectional coverage.
The Infinite Slope and Gauder approach is the other end of the spectrum.