Gamelan are found in the Indonesian islands of Java, Madura, Bali, and Lombok (and other Sunda Islands), in a wide variety of ensemble sizes and formations. In Bali and Lombok today, and in Java through the 18th century, the term "gong" has been preferred to or synonymous with gamelan. Traditions of gamelan-like ensembles (a well known example of which is Kulintang, sometimes called "gong-chime ensembles" by ethnomusicologists) also exist in the Philippines, Malaysia and Suriname, sometimes due to emigration, trade, or diplomacy. More recently, through immigration and local enthusiasm, gamelan ensembles have become active throughout Europe, The Americas, Asia, and Australia.
Although gamelan ensembles sometimes include solo and choral voices, plucked and/or bowed string and wind instruments, they are most notable for the large number of metal percussion instruments. A central Javanese gamelan ensemble includes:
metallophones, such as the saron, gendér, gangsa, and ugal (sets of metals bars laid out in a single row and struck like a glockenspiel)
cradled gongs called bonang and kenong (sets of large, drum-shaped gongs laid out horizontally on stands)
hanging gongs called kempul and the large gong ageng
xylophone-like instruments called gambang (similar to saron and gendér but with wooden bars instead of metal ones)
drums called kendhang
Metals used include bronze, brass, and iron, with a 10:3 copper-to-tin bronze alloy usually considered the best material. In addition, there are gamelan ensembles composed entirely of bamboo-keyed instruments, of bamboo flutes, of zithers, or of unaccompanied voices with the functions of metallophones or gongs in the metal ensemble transferred to surrogates.
Gamelan music is built up in layers. At its centre is a basic melody (core melody) known as the balungan. Further layers, including singing in vocal pieces, elaborate upon this melody in certain ways, but the notes of each layer of music relate to the balungan, and generally coincide at the ends of phrases (called seleh in Javanese). There are also a set of instruments which delineate a colotomic structure, usually ending in the stroke of the largest gong.
