Arny,

This information is probably in this thread somewhere, but it has
gotten so long and convoluted that it's much easier just to ask: Are
you asking whether FM (Doppler) modulation at the high frequency is
the ONLY effect that results when that high frequency in addition to a
low frequency (purposely left undefined since the actual values depend
on a number of factors in the physical setup) are reproduced in the
same transducer, or is there some amount of AM modulation as well?

"The Ghost" gave me an idea for determining this without requiring any
measurement of the instantaneous cone displacement. Perform an FM
discrimination of the received (microphone) signal at the high
frequency "carrier." Call the discriminated signal m(t). Regenerate a
perfect FM signal using the modulating signal m(t) and subtract that
from the original signal. The result is the residual modulation on the
signal, which could then be AM-detected to determine if AM is present.

Three practical issues which must be dealt with come to mind:

1) How to synchronize the regenerated FM carrier amplitude to the
original FM amplitude? Easy answer: emit a signal consisting of the
high frequency tone alone for a length of time adequate to measure the
amplitude.

2) What modulation index, or depth of modulation, should be used in
the regenerated FM signal? Said another way, what gain (if any) should
be applied to m(t) when regenerating the FM signal?

3) How do you synchronize the regenerated signal in time with the
original signal? There are actually two synchronization tasks to be
done: phase synchronization of the carriers, and delay in the modulating
signal, i.e., tau in A*m(t-tau). (A is the parameter in question 2).

Does this make any sense?
--
% Randy Yates % "My Shangri-la has gone away, fading like
%% Fuquay-Varina, NC % the Beatles on 'Hey Jude'"
%%% 919-577-9882 %
%%%% % 'Shangri-La', *A New World Record*, ELO
http://home.earthlink.net/~yatescr