Experimental and theoretical work indicates that point defects can significantly affect sound velocities. Since point defects may exist in thermal equilibrium, their effect on sound velocities may be calculated as an activation phenomenon. Alternatively, activation parameters may be calculated from sound velocity data. Because of the shape of the goetherm it is possible to treat the low velocity zone using the theory of activated processes. The activation parameters calculated from Vp and Vs are in reasonable agreement with one another and with values determined from laboratory experiments on electrical conductivity of olivine and orthopyroxene.