(Fr. table d'harmonie; Ger. Resonanzboden; It. piano armonico, tavola armonica).
The thin sheet of wood in a piano, harpsichord, clavichord, zither, or the like, that serves to make the sound of the strings more readily audible and helps to form the characteristic tone quality of the instrument. A string presents so small a surface to the surrounding air that its vibrations cannot set the air into vibration with any great efficiency; as a result, the sound produced by a string in the absence of a soundboard, although it may well sustain for an appreciable time, is hardly loud enough to be used for any musical purpose. The soundboard, coupled to the strings by means of one or more bridges over which they pass, provides a larger vibrating surface so that the air can be set into vibration more efficiently and a louder sound can be heard. The soundboard does not serve as an amplifier in the same sense as an electronic circuit or device, since it adds no energy from an outside source; rather, it enables the energy already imparted to the string by a hammer, plectrum, tangent, or the like, to be dissipated more rapidly, so this energy is converted to a sound of higher intensity that lasts for a shorter time. The particular resonance and vibrational characteristics of the soundboard determine which components of the complex vibration of the string will be given particular prominence, and the rate at which they will be dissipated; consequently the shape, thickness and ribbing of the soundboard are of primary importance in determining the quality of the instrument of which it is a part.
EDWIN M. RIPIN