Most of the present text is devoted to a«passive» cochlea, i.e., to cases in which the mechanical energy generated by«active» outer hair cells is absent or negligibly small. In spite of the fact that a part of the travelling wave energy is transformed into frictional heat, the velocity amplitude of the basilar-membrane oscillation increases with increasing distance from base.

At some place, namely at the«passive peak» that increase stops, and at greater distance from base, the amplitude quickly drops to small values. At high [low] sine-tone frequency, the distance from base of the passive peak is short [long]. That travelling cochlear wave is the main topic of the present text.