The municipal public address (M.P.A.) system for disaster prevention is an important information facility in communities. The speech intelligibility of such a system, however, tends to be deteriorated by multipass echoes with long time delay owing to reflections from nearby buildings and by the sounds from loudspeakers covering other subareas. When designing such an M.P.A. system, a tool effective for the prediction of outdoor sound propagation should be developed. For this purpose, the authors have been investigating the applicability of a computer modeling technique based on geometrical acoustics. To elucidate the effectiveness of the modeling technique, two case studies were examined by comparing impulse responses (echo diagrams) calculated by computer modeling and those obtained by field measurements. As a result, it was found that this modeling technique can be effectively applied to the prediction of outdoor sound propagation and the basic design of M.P.A. systems.