A Dictionary of Music and Musicians/Belly (pianoforte)
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BELLY or SOUNDBOARD of pianoforte. (Fr. La Table d'harmonie; Ital. Tavola armonica; Ger. Resonanzboden, Resonanztafel). The broad flat of wood, usually of Swiss pine, extended under the strings of a pianoforte, and connected with them by a bridge of hard wood over which they are stretched, is technically called the belly, but is also called the sound- or sounding-board. The strings when set in vibration, owing to their small surface in contact with the air, would be scarcely audible, were it not for the belly, an auxiliary vibrating body of large surface, to reinforce them. Thus the tone of a pianoforte essentially depends upon the movement and variable pressure of the strings at the point of contact with the bridge, by which their vibrations are conveyed to the belly to be intensified by the vibrations of the fibres of this elastic support. There is no sonorous body for which we may calculate movement under varied conditions, and then verify the calculation by trial, to compare with a stretched string. The problem is far more complicated of a resonant surface, as the belly, and appears to have offered less attraction to research. We are mainly indebted to Chladni for what we know of the forms of vibration of resounding substances. His determination of the nodal lines by means of fine sand placed upon vibrating surfaces has been of great importance to theory, and has been the foundation upon which the law of the practice of ribbing the belly diagonally to the direction of the grain with slender bars of pine has been finally established by Dr. Schafhaeutl, who has proved that this contrivance creates nodal lines of rest, and prevents the transversal vibration of the belly as a whole which would be inimical to the production of tone. But up to this time, in the construction of bellies, experiment alone has effected what has been achieved. The difference in the character of tone of pianofortes by different makers, depends very much upon variations in the proportions, direction of the grain, and barring of the belly; but as other important variations of structure invariably and simultaneously exist, the question is too complex ever to be satisfactorily answered. The further description and history of belly will be found under Pianoforte.
[ A. J. H. ]