The stereo cilia bundle extrapolative from inner auditory hair cell swing with a swing in adjacent fluids. Bundle disturbance causes a virtual motion among adjacent stereo cilia within the bundle, stretching a slender thread unifying them. At great distances, the tension causes trap doors to open (figure b). Figure c indicates exerted pressure by the hair bunch in feedback to experimentally forced displacements. This explains why the bundle similar to a simple spring at various deflections. Midway it has an area of minus stiffness. (k = df/dx is a representation of a + constant).
Treating the bundle as a set of N stretchy unit in analogous. Each part has dual springs. One of constant k, balanced at location xa, to represent tip link filament. Next with kb and xb for its parameters. The primary spring attach thru a fixed element. If the hinge is open, the accessory position is a δ left of closed