"Ben Bradley" wrote in message
...
On Sun, 15 Aug 2004 00:37:44 -0700, Bob Cain
wrote:

If the distance from the driver is not changing, there is no
Doppler shift.


I wrote:

The distance from which part of the driver? The frame? The cone?
Something else?

The rest position, the one it will settle to when the
driving signal is removed. If the driving signal contains a
DC component, and the piston is not restrained by a
compliance, then and only then will Doppler shift occurs.
Hard to swallow, I know but it is the truth.

Okay, Bob, I'm going to add a DC component, but I'm not going to
tell you that this DC component is really a millihertz-frequency sine
wave. How will you know the difference? Just what IS the difference
over a time period of one second?

Here's a simple way out of this one, with a very slow oscillation of a
varying DC component, the cone won't be moving at a high enough velocity to
generate doppler distortion, even if it is moving two or more inches p-p.
Forget millihertz, even one hertz at 2 inches displacement is going to be a
peak velocity of less than one half foot per second. At that velocity, it
simply doesn't have time to dopple!:-)