We're on vacation to celebrate my birthday but my mind's never far from audio.
When I am considering a problem I often imagine the impossible in order to explore the possible. This process helps free my mind from rehashing prior art.
My impossible thought was to create a speaker where one set of drivers handles the low amplitude signals while at the same time a second set supplements the first when the loudness increases beyond a certain level. This would help the problems of Doppler (where one cone moves both far and near at the same time) experienced in drivers—and not experienced in an actual musical instrument.
I've done something like this before. Years ago I built an experimental speakers system with amplitude sensitive side-firing drivers that kicked in only on loud passages. The reason I did it was different than this idea, but the results would be similar. (Back then, and still now, I am fascinated with the idea of the soundstage width increasing over a certain loudness).
This idea of low and high amplitude drivers has a couple of serious flaws, not the least of which is how to separate the two amplitudes. Imagine an orchestra playing both loud and soft passages at the same time: the violins at a soft to medium level while the trumpets blare. From the recording perspective, the trumpet blasts are mixed in with the aggregate violin as one waveform. It would be almost impossible to separate them.
Still, an interesting thought.