interesting thread, i'm an avid collector of all things hi fi, and old speaker books rate quite highly
the standard crossover is cheap, easy to couple speakers with, and can be easily tailored for a flatish sound, at the expense of a little quality
i dont see it being replaced in the near furure,
john, thanks for the nice comments about my old speakers
but there s no magic dust, i'm lucky enough to have bought/ collected lots of good quality drivers, so i can use combinations of drivers that manufactures could not use, for my one off creations.
there is no one 'right' way - single drivers or multi drivers.
there are ways of mechanically restricting/ boosting drivers across the audio band. most ways have neen used in the past by someone, thats exactly what most single driver speakers do.. they are mechanical 3 way speakers
i remember a knowlegable enthusiast saying to me speaker designers he knew, design using sharp cut crossovers.. but use 1st order themselves.
I was an avid single driver user once, but not now..
collector and DIY user of old british triode valves
Open baffles / single ended diy px4 and px25 valve amps