"Bob Cain" wrote in message
...
Doppler shift is an unquestionable phenomenon, easily proved
from first principles. The thing is that it depends on a
sound source that is moving with respect to, i.e. _within_
the medium (we assume for this that the listener is
stationary with respect to it.) A piston with two
frequencies driving it and stationary with respect to the
medium otherwise will supposedly show those frequencies
modulating each other. The flaw is that the piston is not
in any sense moving within the medium, it is moving the
medium which is fundamentally different.

I don't understand. Explain to me how the speaker actually transfers the
energy to the air. Maybe you can do that by contrast. Suppose I hit my
knuckle on the table. I can't see the table vibrate, but I know it does. The
energy moves from the molecules in the table to the molecules in the air. I
can live with that.

Then I watch the speaker diaphragm move. Sometimes it moves a lot, sometimes
a little. At one point during the movement is the sound wave created? I know
it pushes air to create a "breeze" but that's not the sound wave. I'm
guessing that when the forward movement stops, the pressure goes back to
"normal" and the sound wave is formed.

Is that how it works or am I still struggling with truly understanding the
mechanics of how a speaker works? I know how it works in layman's terms, but
I'm fuzzy about the actual mechanics of getting those molecules smacking
into each other.