Abstract
In predicting and controlling the propagation of noise in the open air, it is very important to take account of the shape of a building that is the noise source, the cross section of railway track and road, as well as barriers and surrounding buildings. Then, the theory of the free-field diffraction of a spherical sound wave by a thin half-plane is basically necessary and the rigorous solution was given by H. M. Macdonald long ago. However, the rigorous solution is hardly used in calculating noise reduction in the design of barriers etc., and instead, Maekawa's experimental curve is widely used. But the range of application of the experimental curve is limited, because which is obtained by experiments to satisfy the Kirchhoff's approximate conditions. In the previous paper the detailed behaviors of Macdonald's rigorous solution were clarified by numerical calculation, and it was shown that all experimental results were in a very good agreement with the rigorous solution no matter where a source and an observating point were located, and that the approximate formula of the rigorous solution given accurately by Bowman & Senior had little approximation error. In this paper a new simple approximate formula of the rigorous solution is presented and a practical method based on the new approximate formula is proposed for the prediction of the propagation of noise, by which the detailed peak-dip due to interference between several waves are not drawn in the sound pressure level distributions but only monotonous gradual variations are drawn.
