Of course it will. And its instanteious velocity is added to the
instantaneous velocity due to the upper note.

Okay, but it seems like people are saying that this isn't the case, and
is the reason doppler distortion would NOT occur, which seems plain
bizzare, IMHO. Surely, as the lower frequency moves the cone back and
forth, which at the same time is vibrating to create the higher
frequency, that is IDENTICAL to moving a single vibrating source back
and forth, like the train analogy (except the train doesn't move back
and forth unless the driver is very confused). Therefore, the doppler
effect surely DOES occur.

It just seems really obvious, so I must be missing the whole point of
this, I'm no physics scientist !

--
Mark Simonetti.
Freelance Software Engineer.