The angular distribution of sound incident on a panel or opening

A theoretical method has been developed for predicting the directivity of the sound that is radiated from a panel or opening excited by sound incident on the other side. This directivity needs to be known when predicting the sound level at a particular position due to sound radiation from a roof, wall, ventilating duct, or chimney flue. The method uses a two‐dimensional strip model and the low‐frequency result for a square piston. It was found necessary to use a weighting function in order to account for the angular distribution of the incident sound. Initially a cosine squared weighting function with a weighting angle parameter was chosen and the weighting angle parameter was varied in order to obtain the best agreement with experiment for the particular situation. This talk will describe the theoretical development of weighting functions, which are based on the actual physics of each situation. Situations that are covered include an opening or panel on the surface of a room and an opening at the end of ...