Tong Chen
Inst. of Acoustics, Acad. Sinica, 100080 Beijing, People's Republic of China
Temple bells in Korea are quite special as compared with bells in other countries. The bell has a tube on its head and a pit or cavity (``rumbling structure'') under it. The acoustical behavior of the bell and its pit has been modeled as a cylindrical cavity with an air gap. The air gap changes the mode frequencies and damping factors of the cavity; the damping factor increases sharply with increase in length of the air gap, especially for some modes. In real cases, the air gap between the bell and the rumbling structure is limited to 0.3--0.4 m. The tube on the bell is effective for radiation of sound only when its length is nearly an integer times the half-wavelength of a cavity mode. It is reasonable to adjust the tube length for the most prominent partial in the bell sound, which determines the strike note. The acoustic mode frequencies can be tuned by adjusting the depth of the pit and the length of the tube to improve the timbre of the bell sound.