Evaluation of high-powered outdoor sound systems

Outdoor installations of high-powered sound systems have been made for the purpose of communicating over large areas from systems located on tall buildings and on airplanes. In order to evaluate the performance of these systems it is necessary to use actual speech materials rather than perform simple physical measurements. Airborne systems are affected greatly by the Doppler shift in frequency which cannot be accounted for in a physical evaluation of a system and reflections from buildings introduces echoes for which it is impossible to calculate the effect upon intelligibility. Speech materials have been used to determine both the intensity levels as a function of distance and angle, as well as the intelligibility of the system for various power levels. The results of these studies lead directly to the design of more efficient communication systems. The application of the results of two studies is shown for the design of optimum systems.