Investigation Of Bracings Transformations On Voboam Guitars: What Can Uncalibrated FEM Models Tell Us?

The Baroque guitar was one of the most popular instruments among the French nobility, especially at the court of Louis XIV. The instrument makers of the Voboam family (1640-1731) helped to set the standard for Parisian Baroque guitars, particularly in terms of proportions and decorative features. Twenty-nine guitars of these makers are still extant, among which nine are preserved at the Musée de la musique, Paris. These instruments exhibit significant material transformations which are part of the instruments’ material histories. Various modifications of the bracings glued underneath the soundboards are prone to have a strong impact on the vibrational behaviour of the instruments. This paper aims to provide answers to clarify the intention behind these transformations. Using 3D scan imaging, the dimensional differences of the eight soundboards are proved to be small enough to create one numerical model whose soundbox is representative of the corpus. The influence of two allegedly “typical” bracings on the vibration modes is then studied using X radiography and Finite Element Modeling (FEM) analysis. The dynamical analysis, coupled with uncertainties analyses, show that the lack of knowledge about material and geometrical parameters is too high to draw conclusive statements about bracings influence.