Field experiment on sound propagation from an elevated directional source

The authors investigate outdoor sound propagation from a directional source by field experiments. Results on ground-to-ground sound propagation are reported in this conference by another paper. In addition to an experimental investigation on ground-to-ground sound propagation from a directional source, in this report, results of an experiment on air-to-ground sound propagation from an elevated directional source lifted by a tethered balloon is described. In this experiment, a horn type loudspeaker was raised at the heights of about 100 and 200 m, and sound propagation characteristics from the source to receivers on the ground were analyzed from impulse responses measured by a swept sine method. As a result of the experimental study, which was made under a meteorologically calm condition, it was confirmed that the sound propagation characteristics can be accurately estimated by considering the directivity characteristics of the sound source in low and middle frequencies, and that they are considerably affected by meteorological effects.