This whole argument is based on the wrong assumption that the high
frequency source is "riding on" the low frequency source like a whistle
on a train. It is NOT!

Sorry, but it is. See my previous postings.


Both sounds are being produced simultaneously by the
complex electrical waveform driving the speaker cone which moves in
accordance. Assuming that the speaker is being driven within its linear
limits, the cone's motion accurately follows the driving signal, and it is a
linear system.

Doppler "distortion" is not the result of non-linear distortion.