Our Indonesian Thunder Drum is made with a spring attached to the diaphragm, so when it is shaken the spring moves and creates a continuous resonance through the body of the instrument. This results in a sound very much like thunder, thus the name Thunder Drum! ♫ Handmade in Bali. ♫ Hardboard and Mylar, with 17ö steel spring. Measures 3" x 8". ♫ Please allow for variation in color and design of these truly remarkable instruments.