Instruments that produce sound from the substance of the instrument itself (wood or metal) are classified as idiophones . They are further divided into those that are struck, scraped, plucked, shaken, or rubbed. In the Philippines, there are metal and wooden (principally bamboo) idiophones. Metal idiophones are of two categories: flat gongs and bossed gongs,. Flat gongs made of bronze, brass, or iron are found principally in the north among the Isneg , Tingguian , Kalinga , Bontok , Ibaloi , Gaddang , Ifugao , and Ilonggot . They are commonly referred to as gangsa . The gongs vary in size, the average are struck with wooden sticks, padded wooden sticks, or slapped with the palm of the hand. Gong playing among the Cordillera highlanders is an integral part of peace pact gatherings, marriages, prestige ceremonies, feasts or rituals. In Southern Philippines, gongs have a central profusion or knot, hence the term bossed gongs . They are of three types: 1) sets of graduated gongs ...