Bob Cain wrote in
:



The Ghost wrote:

Does your prediction of 0.2% distortion apply to the situation of a
piston in a tube or a piston in an infinite baffle, or doesn't it
matter?

First, that prediction is incorrect (I realized this
morning.) I accidentally plugged the 2 cm in as velocity
rather than displacement when doing the calculation but .2%
is correct for a magnitude .01 m/sec LF velocity.


Yes, I know. I asked the question because I knew the prediction was
incorrect for a tube and because I wanted you to confirm that it was for a
tube before I called attention to what was a very glaring and clearly
incorrect prediction.


The correct figure for 40 Hz at 2.53 m/s (2 cm throw) and 2
kHz at .05 m/sec (approximately equal acceleration, as is
closer to the situation with a driver in a cabinet) is about
25.4% RMS IM distortion. I find this rather startling.

The sidebands around the 2 kHz signal are -15 dB, -36 dB,
-60 dB, -87 dB.


Since you failed to mention prior work on this problem, or acknowledge its
validity, I will simply state that the -15dB sideband level is in good
agreement with the prediction of Art Ludwig's prior analysis of Doppler
distortion in a tube.