Comparison of theoretical and experimental results for the directivity of panels and openings

A theoretical method has been developed for predicting the directivity of the sound that is radiated from one side of a panel, or an opening, which is excited by sound incident from the other side of the panel, or the opening, from a room or duct. This directivity needs to be known when one is predicting the sound level at an external position which is due to the radiation of sound from the roof, wall, ventilating duct or chimney flue of a factory. The theoretical method is essentially a two dimensional method, although it does include some three dimensional considerations. This paper compares this theoretical method with published experimental data. The theory presented in this paper agrees with the average trend of the experimental measurements. However the experimental results show significant variability about the theoretical predictions. This is believed to be due to both experimental and theoretical difficulties.