I think that you missunderstood me - the bass unit is modulating the tweeter depending on cone placement.
In Erins measurement theres only the tweeter sounding in this particular measurement. On the bass unit he has a battery, no amplifier.
And the difference in frequency response is big for the tweeter depending on where the bass cone is.
No I didn't misunderstand you. I explained that by the time the woofer is moving that much, the distortion it generates is much of a concern than whatever tweeter is doing.
Theoretically, the effect of "directivity modulation" of the tweeter, by excursion of the woofer, already occurs when the woofer still shows linear excursion.
In a general thread about coaxial speakers I had once simulated this for a driver with 10cm cone with +-3mm excursion.
The woofer of the KEF LS50 should also have at least (rather more) +-3mm linear excursion.
I have summarized the results as an animation, so one can better see the effects of the different cone positions:
1. Cross-sectional sketch, tweeter (blue) with different cone positions
2. Normalized frequency response
3. Normalized sonogram
At +-3mm excursion of the woofer, the "directivity modulation" only has a noticeable effect on the radiation of the tweeter at frequencies above 6kHz.
The question now is whether this already leads to perceptible psychoacoustic effects. The states shown in the animation are not stationary, but change with the frequency of the low-frequency reproduction.