"Porky" wrote in message


I think you're right, Bob, that certainly seems logical to me. If it
is Doppler distortion, the tone should be vary in a continuous warble
from -50Hz to +50Hz because the woofer's velocity is continuously
changing.

The FFT plots are snapshots of a kind, but they are also time-exposures. 1
million points at 96 KHz is about 11 seconds worth of data. It is all
averaged together in those pictures.

If one uses a low enough modulating frequency, and a small enough sample
set, snapshots with a faster effective exposure times result.

One can then actually can see the carrier warbling. It will show up at
different frequencies at different times in a sucession of snapshots.

However, with a long exposure you see the results averaging of about 550
cycles of the 50 Hz tone.