It is well-known that the dynamical matrix is represented by the inverse dielectric matrix. We show that the temperature dependent part of the velocity of the longitudinal acoustic phonon can be given by only one element of the dielectric matrix ε(q, q) in the ordered state of Cr if the random-phase approximation is applicable and the Bloch wave functions can be expressed by the atomic orbital functions for the system. The same result hold in other metals if above conditions are satisfied. In the limit q→0 the element ε(q, q) has the intimate relation with the density of states at the Fermi energy even in the ordered state of Cr which decreases with decreasing temperatures. Our theory gives one of reasons of the remarkable increase of the compressional constant C11 of single crystals of Cr in the spin density wave state with decreasing temperatures.51721362142