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 potential sound 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 - one possibly original, and one ”typical” of a latter modification - on the vibration modes is then studied using X-radiography and FEM analysis. The dynamical analysis is then coupled to uncertainties analyses to evaluate the influence of material and geometrical lack of knowledge on the results.