An analysis of the transmission of sound through sandwich panels (consisting of lightweight, flexible cores between relatively stiff skins) is presented here. First, previously given results for the free vibrations of such panels are analyzed and unified. Then, a traveling‐wave analysis is used to obtain impedances and transmission‐loss formulas, which are in turn compared with previously published experimental data. The comparison is relatively good, and confirmation of a symmetric coincidence effect is obtained. Further, the numerical results indicate that this symmetric coincidence generally occurs at a much lower frequency than does antisymmetric (shear wave) coincidence.