Hanging bossed gongs in a traditional Gamelan percussion orchestra (Yogyakarta, Java Island)
The largest gong (on the left) is called Gong ageng.
For more information about Gamelan, read en.wikipedia.org/wiki/Gamelan
For more information about gongs, read en.wikipedia.org/wiki/Gong and en.wikipedia.org/wiki/Gong_ageng