Observability of acoustical and optical localization

A ``pseudosphere'' approximation is introduced to describe quantitatively the localization of acoustic and optic waves. The localization length is obtained in terms of experimentally accessible parameters (scatterer density and size, speed of sound or light, frequency). For d=3 it is predicted that acoustic Anderson localization will not be observed unless the scatterers are more efficitent than hard spheres. A phase diagram for the optic problem is obtained; it suggests the sudden onset of localization at moderate values of the scatterer density.