A metallophone is any musical instrument consisting of tuned metal bars which are struck to make sound, usually with a mallet. Metallophones have been used in music in Asia for thousands of years. There are several different types used in Balinese and Javanese gamelan ensembles, including the gendér, gangsa and saron. These instruments have a single row of bars, tuned to the distinctive pelog or slendro scales, or a subset of them. The Western glockenspiel and vibraphone are also metallophones as they have two rows of bars, in an imitation of the piano keyboard, and are tuned to the chromatic scale. In the Hornbostel-Sachs classification scheme they are categorized as a sub-category of “percussion plaques” 111.22 Percussion plaques.