Figure 1. Anatomy of the ear.

(a) Sound causes a pressure vibration p₃ in the ear canal and a motion of the ear drum (area A_a). The middle ear’s ossicles, namely the mallus of length l_a, incus of length l_w, and stapes convey the motion to the inner ear, or cochlea, to vibrate the oval window (area A_ow) and the round window (area A_rw). The pressures p₁ in the scala tympani and p₂ in the scala vestibuli change accordingly. (b) A transverse section of the inner ear shows the basilar membrane separating two chambers of cross-sectional area A₁ and A₂. Vibration of the membrane (velocity V_bm) and deformation of the cochlear bone, at constant circumference, lead to area changes a₁ and a₂.