Why bundengan musicians always soak their instruments before playing

Normally, water is associated with risks and problems for musical instruments. Even a slight change of humidity could alter the mechanical and acoustical properties of the instruments, affecting their musical quality in a negative way. This perspective is shared among most musicians, craftsmen (i.e. instrument makers), as well as cultural materials conservations. We would not want our guitars and our violins, for example, to be wet when they are stored and when they are played. It is therefore considered extraordinary that the bundengan, an Indonesian traditional musical instrument, is preferably played in a wet condition. In the old days, this instrument was even played under the rain. Why do the bundengan musicians play this way? In this paper, we explore the physics of why wetter bundengan sounds better. The key of this phenomenon is the bamboo culm sheaths, which deform when interacting with water. When a dry bundengan is made wet by the musician, the bamboo culm sheaths curl and become better connected, such that these sheaths vibrate together as a group, generating a sound with a lower frequency and a longer sustain than the sound of a dry bundengan, therefore better at imitating the sound of a metal gong.