Gongs are musical instruments made of alloy bronze, sometimes with gold, silver, or black bronzeadded to their composition. In the Kinh language, the word cong identifies convex gongs and the word chieng refers to the flat ones. Gongs vary in size from 20 to 120 cm in diameter. Gongs may be played one at a time or in groups of 2 to 20 units. The Muong, as well as other ethnic groups in the Truong Son-Tay Nguyen regions, use gongs not only to beat the rhythm but also to play polyphonic music. Ensembles of gongs usually include several sets that vary in number and function during the performance. Gongs can be struck with wooden sticks, mallets, or even bare hands. There are techniques that can be used to shut off sounds and to produce melodies. In some ethnic groups, gongs are only intended for men to play. However, the sac bua gongs of the Muong are played by women. In other ethnic groups, both men and women may play. In general, taboos regarding cong-chieng customs differ from ethnicity to ethnicity. Gongs hold great significance and value for many ethnic groups in Tay Nguyen. The gongs play an important role in the lives of the inhabitants of Tay Nguyen; from birth until death, the gongs are present at all the important events, joyful as well as unfortunate, in their lives. Almost every family has at least one set of gongs. In general, gongs are considered to be sacred instruments. They are mainly used in offerings, rituals, funerals, wedding ceremonies, New Year festivities, agricultural rites, victory celebrations, etc. In the Truong Son-Tay Nguyen region, playing the gongs electrifies the people participating in dances and other forms of entertainment. Gongs have been an integral part of the spiritual life of many ethnic groups in Vietnam.