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This is in reply to your search for a demonstration cochlear model.
Another way to go is a purely mechanical model. In the 1950s I was
fortunate to share a laboratory room at Harvard's Psychoacoustic
Laboratory with Bekesy. He constructed a cochlear model by hanging
closely spaced steel(?) balls from string along a 4-metre long beam.
String lengths changed from "base" to "apex." When the beam was rotated,
you had a Helmholtz cochlea; one ball would resonate to the frequency of
When adjacent vertical strings were connected with short horizontal
strings, with a smaller weights in the middle of each connector, you had
a continuous membrane model, and a Bekesy cochlea. The system could be
driven by swing the basil (oval window) end pendulum, or by rotating the
beam. In either case a traveling wave was generated, which settled to
maximum action at the appropriate point, with a clear effect of critical
band as adjacent pendulums acted with less amplitude.
Bekesy made a movie of the model, which was quite lovely, with the
sinuous traveling wave viewed from the end of the model and growing
activity at one location. I believe the movie was shown at an Acoustical
Society meeting around 1955 or 56.
I wonder if a copy of that movie exists; it would be great to have it
available for the kind of demonstration you contemplate.
All the best,
C. Douglas Creelman 416-690-9407 (phone & fax)
9 Fernwood Park Ave. 416-708-9407 (cell)
Toronto, ON Canada creelman@xxxxxxxxxxxxxxxxx