"zigoteau" wrote in message
om...
Bob Cain wrote in message
...

[snips]
Art must like it loud. At 40Hz, let's say the speaker diaphragm has an
rms amplitude of 1e-2 m. Its rms velocity excursion v is 2.4 m.s^-1,
and hence the power flux is Z*v^2 = 2471 W.m^-2. Sound intensities are
normally expressed in dB wrt 1 pW.m^-2. This works out at 154 dB. This
may be compared to the following table from

First off, this is not the example I include on my site. I use a velocity of
1 m/s at 50 Hz, and this is just to generate some convenient numbers which
can easily be scaled. Second, the relationship you use is valid for a
piston in a tube, but for the real world case of a piston in a baffle the
sound output is much less because the real part of the impedance seen by the
diaphragm is much less than your Z. At 50 Hz a 1 m/s velocity corresponds to
a peak displacement of 3 millimeters which is quite realistic for a woofer.
I invite any educated physicist to look at my site and decide for him or her
self if my derivation is valid. It can be seen at

http://www.silcom.com/~aludwig/Physi...on/dopdist.htm

As you pointed out, I assume the linear wave equation in this derivation,
and for very high velocities, or for propagation in a tube, the
non-linearity of air can be important. I have now analyzed the solution to
the nonlinear acoustic equations as well. That analysis is at

http://www.silcom.com/~aludwig/Physi..._acoustics.htm

Art Ludwig