The radiation characteristics of a magnetohydrodynamic (MHD) acoustic transmitter radiating into a free medium are examined. Two source mechanisms are associated with the transducer: an electromagnetic force associated with the MHD operation, and a density fluctuation associated with heating of the medium by an electrical current. The wave equation is derived and a solution is found for impedance boundary conditions using a Green's function approach. Measurements obtained in a large water tank are shown to compare favorably with the predictions.