Cochlear mechanics: coiling effects (I, II) and the absorption equation (III).

Mechanical effects of cochlear coiling are examined by comparing wave propagation in straight and coiled two-dimensional models. (1) Compressional waves PC speed up in the coiled system and PC lambda/4 resonance frequencies differ between models by about 1/2 octave. (2) For transpartitional waves PT, there exists a condition of complete model equivalence. (3) Straight models with equal, instead of equivalent depths underestimate coiled PT speed in the long wave limit. (4) Straight model theory alone fails to predict that there is a special radius relation for maximum coiled PT speed at long wave lengths. (5) The case of near-zero modiolar radius is interesting in connection with responses to the stapes near-field. It is suggested that the simple physical assumption implicit to most PT integration procedures has been, that the longitudinal power flow drops at twice the relative rate of the local fields. Two new equations are obtained: the 'absorption equation' and the equation for 'absorption tonotopy'.