Posted by MAP on October 10, 2002 at 12:28:28:
In Reply to: Ugly SALLIE....? posted by Terry Koehn on October 09, 2002 at 15:10:41:
Greetings TK,
It's interesting to consider two examples of what you're proposing: first, a rear diaphragm which is held stationary by a forcing function, and second, a rear diaphragm which is forced to create a displacement which is equal and opposite to that created by the front diaphragm. Note that the first is the equivelant of mounting the front diaphragm in a closed box, and the second is the equivalent of a bipolar (not dipolar) pair of radiators, also working in a closed box.
The sole distinction here is that the "box" would most likely be a very small volume of air trapped between two very large diaphragms. This constitutes an enormous acoustical stiffness, which goes as area^2/volume. The speaker's bass response would, therefore, be enormously attenuated - perhaps by whole decades of dB. The only solution would be to drive the diphragms with much higher force, but even then, dielectric breakdown severely limits the outcome.
So that's why Dr. West didn't have much of a reaction. It's because a.) it's very impractical, and b.) it's not easy to explain in a short communication.
Best,
MAP