Gongs of the gamelans have a remarkable musical sonority. It is partly by virtue of the knob. The knob, called peñcu in Javanese, moñcol in Balinese, is a round protuberance at the gong's center.
The knob characterizes South-East Asian gongs and hence those of the gamelans. The side wall of these gongs is deeper and the wall is often stronger than among a second type gong. A gong possessing these physical features, the peñcu above all, emits an exact note through a pure and strong vibration. The same principle takes place when one fixes a mass onto the center of a drum membrane. The membrane sets to vibrate according to a fixed note. One can adjust the note's pitch by changing the mass's weight. Without the aid of a mass, the drum membrane gives normally a sound of non definite pitch.
Why are the gongs of gong chimes knobbed ?
Having a peñcu, South-East Asian gongs give an exact note. They possess thus a melodic potential that one exploits by forming them into chimes. A chime of first or second type gongs would not be as claimed a melodic instrument as is a gamelan's trompong.
Physical proportions of the gamelans' gongs are so various that one discovers here the biggest wealth of gong shapes of all Asia.
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