Concentric drivers

@mulveling  😃 *kazoo fanfare*  And thanks for that byte of info yours unruly was unaware of, but not now... makes it work, despite itself. *L*

Flip phase, and a crossover tweak.  'Pepperpot' backside shaped to act as a default waveguide, audible Magik...(google that...;)...).

That's why I like Walsh drivers.  Simple, just stack vertically and cross proper. *S*  The rest is mechanics and material magic.

...and beats having to move speakers Really Fast to compensate for Doppler fx.

Something for your and all's late Sat./early Sun. :

Is there a confusion between Doppler effects and phase alignment / distortion here?

Doppler effects occur when there's movement between the source of the sound and the listener, as noted with the car horn example.

Phase distortion occurs with multiple drivers having the voice coil/cone intersections not physically aligned, which is what JBLs' L250 addresses with the sloped cabinet faces (and judicious driver 'tweaks' I suspect).  That, with toying with the crossovers design, ought to have minimized phase issues.

The original Ohm speakers were single driver affairs, so no phase problems.  The current Ohm speakers with their tweeters mounted directly over the inverted drivers 'average out' phase issues.  Since the voice coils are at a right angle in relation to each other, one could say they're aligned.....kinda... *G*

Concentric drivers can't have the coils aligned, ever.  Perhaps the tweeters' backside structure is acting upon the wavefront from the woofer behind it, but the physics involved goes off into the deep end of the pool imho.... ;)