Illustration demonstrating mechanisms that produce a loss of efficiency. For both OHC protein piezoelectricity and bundle flexoelectricity, power is lost at low frequencies due mechanical stiffness, in the mid-band to viscosity, and at high frequencies due to viscosity and mass. For the bundle, transverse viscous drag causes even more power loss relative to axial movements at high frequencies. Efferent activation causes a decrease in the efficiency and a change in the frequency of peak efficiency for both the hair bundle and the soma. (Based on results from14, 16).