Sound board (music)
A sound board, or soundboard, is the surface of a string instrument that the strings vibrate against, usually via some sort of bridge. The resonant properties of the sound board and the interior of the instrument greatly increase loudness over the string alone.
The sound board operates by the principle of forced vibration; the board is gently vibrated by the string, and despite their differences in size and composition, the board will be "forced" to vibrate at exactly the same frequency, producing the same sound as the string alone, differing only in timbre. Although the same amount of energy is transmitted with or without the board present, the sound board, due to its greater surface area, is more readily able to transform this energy into sound. In other words, the sound board can move a much greater volume of air, therefore producing a louder sound.
Sound boards are traditionally made of wood (see tonewood), though other materials can be used, such as skin or plastic on instruments in the banjo family. Wooden sound boards typically have one or more sound holes of various shapes. Round, oval, or F-holes appear on many plucked instruments, such as guitars and mandolins. F-holes are usual in violin family instruments. Lutes commonly have elaborate rosettes. A sound board, depending on the instrument, is also called a top, plate, or belly.
In a grand piano, the sound board is a large horizontal plate at the bottom of the case. In an upright piano, the sound board is a large vertical plate at the back of the instrument. The harp has a sound board below the strings.
More generally, any hard surface can act as a sound board. An example is when a tuning fork is struck and placed against a table top to amplify its sound.
- Alberto Bachmann (1975), An encyclopedia of the violin, p. 87