A thin wooden board, to which the vibrations of pianos strings, music box combs, or other sound-producing devices are transmitted, usually by means of a wooden bridge. The soundboard, usually found at the back of a vertical musical instrument or the bottom of a horizontal one, amplifies the sound and contributes to the desired tone quality. In almost all pianos, the soundboard is made of quarter-sawn (or vertical grain) spruce, because spruce is the strongest, stiffest wood in proportion to its weight. In music boxes and other mechanical instruments, it is sometimes made of a softer variety of wood.
MBSI
Musical Box Society International