Abstract
Sound radiation from a sound source of concave shape is analyzed by applying wave theory. In our analysis, we divide a sound source into thin cylindrical subsections whose radii vary gradually, so that the propagation of a plane and higher modes of sound waves in each subsection is calculated in a stepwise manner by solving boundary value problems. It may be expected that the solution of this analysis is applicable to prediction of the sound field radiated from a cone type or a horn type loudspeaker in an infinite baffle. In this paper, some numerical calculations are made for the sound fields of a rigid piston located at a certain depth from an infinite baffle (Fig. 5)and of a rigid cone in an infinite baffle (Fig. 8), and are compared with the values obtained by the usual approximate methods. Fig. 6 shows the dependence of the normalized sound pressure, which is defined by Eq. 50, upon the frequency parameter ka_1 for the case of the rigid piston. In this case, comparing the values obtained by a plane-wave approximation, we may be able to say that they are in agreement with each other in some degree. For the case of the rigid cone, however, there are significant differences between the values by a geometrical acoustic approximation as shown in Fig. 9. The values by the present method fluctuate around the values by the approximate method.
