Concentric drivers

Who cares?  Listen to the speakers with your music at different volume levels, and if you still like sound what difference does it make if there’s a Doppler effect or not? There are ALWAYS trade offs between different speaker designs, which is why your ears need to be the final arbiter.  I’ll also add that I think concentric drivers are time/phase coherent (or maybe one or the other) that may outweigh any Doppler effect.  Let your ears be your guide.  Personally, I think there are much more important speaker issues (cabinet, crossover design/parts, driver quality, etc.) than worrying about the Doppler effect.  Just my $0.02 FWIW. 

@islandmandan , doppler distortion is very real. Most of us have had the experience of a driver leaning on the horn as the car passes us. Right as the car shifts from coming at us to going away from us the horn changes pitch. This is very noticeable. The same thing happens with drivers that are handling the lowest frequencies. To produce low bass drivers have to take long excursions, coming at you then going away. This will cause a change in pitch of the higher frequencies the driver is handling as the driver changes direction. If you can see the cone or diaphragm move this is happening. Woofers that cross over at lower frequencies cause much less trouble than full range drivers. Better yet you can protect the entire speaker by using sub woofers to handle the longer more problematic excursions isolating the speaker from this effect. It is also true that larger drivers do not have to move as far to produce the same volume of bass causing less distortion. I use full range electrostatic speakers and the difference between subs and no subs is not arguable. Even lewm would hear it:-)

As for concentric drivers, they are actually separate drivers with a crossover so the movement of the woofer will not affect the tweeter only the other frequencies it carries. 

I have a pair of Thiel CS6 speakers which have first order crossovers plus a concentric mid/tweeter. This crossover design makes each driver cover a much broader frequency range. Theoretically this would worsen any doppler effect. Other Thiel models have the same characteristic - they use first order crossovers and several models have concentric drivers. Vandersteen is another example of using first order crossovers.

I’ve read dozens of Thiel speaker reviews over the years and I’ve never seen a reviewer mention anything about the doppler effect altering the sound. In fact I’ve probably read over a thousand speaker reviews in my life and I don’t recall anyone ever mentioning doppler. You would think that golden eared reviewers would race to tell you about how their exceptional hearing detected that they were hearing the doppler effects of a particular speaker.

I’m going to stick my neck out and say that the doppler effect for speakers isn’t a thing. I wouldn’t be surprised if some company cited this as a reason why their speakers are better but I suspect that not all marketing hype is real. Except when it comes to cables where you should believe everything the manufacturer says.

I mean if you setup a big speaker on a trampoline and crank up the volume real high, maybe there could be some measurable doppler effect. But there's really not much specifically about a concentric driver to be concerned about.

The woofer does act as a horn extension for a Tannoy's tweeter, but it's never been a topic of discussion or concern, to my knowledge.