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Bekesy model

Dear Christian,
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 rotation. 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,
Doug Creelman

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