Normal modes of a Gamelan Gong

A gamelan is an ensemble of traditional musical instruments from Indonesia and surrounding countries. The backbone of a gamelan is a selection of gongs with a wide range of sizes but a characteristic general shape. Compared with many other percussion instruments these gongs have been incompletely investigated. In the present work we report a study of the normal modes of one particular small gamelan gong originating in Sarawak. A finite-element model of the gong has been constructed and used to calculate the forms and frequencies of its normal modes. These are compared with experimental ESPI results. Agreement is reasonable in view of the lack of precision in the manufacture of the instrument. They show exactly what one would expect of an axially symmetric system subject to reasonably small symmetry breaking. A comparison with the acoustical power spectrum enables us to identify the small number of modes mainly responsible for sound output.