(A) study on the radiation characteristics andacoustic performance of korean bells

Abstract

A study on the unique feature of Korean bells was executed by adopting a appropriate models such as a prolate spheroidal dome or a finite cylindrical cavity. The radiation characteristics and the effect of internal cavity were discussed as well as the role of sound tube. Theories on the acoustic performance of internal cavity developed in chapter 3 and chapter 4 were verified by the experiments before applying to the model. The investigation of the model characteristics of bell body were left due to lack of standards to classify bell sound. The results of numerical analysis such as finite element method agree well with those of experiments, so that the method can be applied to bell design. The radiation characteristics of Korean bells were analyzed in chapter 2, by modelling those as a section of vibrating prolate spheroidal dome with infinite baffle. The characteristics of sound field generated by a certain mode of bell were obtained and the radiation impedances of the modes were discussed by varying the maximum or minimum radius of prolate spheroidal dome. The contour plots of velocity potential show the transition region between cylindrical and spherical wave field. And the pressure response on the surface of spheroid is maximum at the height of man when the ratio of max.dia. to min.dia. is 3.8. The under-and overpressure between adjoining out-of-phase surface elements of the spheroid cancel each other, if the wavelength of flexural wave in radial direction is smaller than that of the wavelength in air as in Fig.2.5. As a result, the maximum contour of pressure locates at a wavelength distance from the body, but the amplitude is smaller than that case of the longer flexural wavelength by 40dB, in general. In chapter.3, the role of cavity composed by the internal boundary of bell and dug ground were investigated and also the sound pressure distribution on the gap area between the bell and the ground was obtained. The cylindrical chamber on which wall piston s...