DIGITAL HERITAGE (2025) Identification of Violin Reduction via Contour Lines Classification

The first violins date back to the end of the 16th century in Italy. For around 200 years, these instruments have spread throughout Europe and luthiers of various royal courts, eager to experiment with new techniques, created a highly diverse family of instruments. In an attempt to normalise violins for European orchestras and conservatories, size standards were imposed around 1750. Instruments that fell between two standards were then reduced to a smaller size by luthiers. These reductions have an impact on several characteristics of violins, in particular on the contour lines, i.e. lines of constant altitude as measured from a reference plane between the violin plates, which look more like a 'U' for non reduced instruments and a 'V' for reduced ones. Those differences between (un)reduced violins have been observed empirically but to our knowledge no quantitative study has been carried out on the subject. In this paper, we aim at developing a tool for classifying violin contour lines in order to distinguish reduced instruments from non reduced instruments. We study a corpus of 25 instruments whose 3D geometric meshes have been acquired via photogrammetry. For each instrument, we sample contour lines at 10-20 levels, regularly spaced every millimetre. Each contour line is fitted with a parabola-like curve (with an equation of the type y = α|x| β) depending on two parameters, describing how open (β) and how vertically stretched (α) the curve is. We compute additional features from those parameters, using regressions and counting how many values fall under some threshold. We also deal with outliers and non equal numbers of levels, and eventually obtain a numerical profile for each instrument. We then applied different learning techniques on those profiles to determine whether instruments can be classified solely according to their geometry. We find that distinguishing between reduced and non reduced instruments is feasible to some degree, taking into account that a whole spectrum of more or less transformed violins exists, for which it is more difficult to quantify the reduction. We also find the opening parameter β to be the most predictive. 1. Historical context and preliminary observations It took around 200 years for the violin family, which dates back to the end of the sixteenth century in Italy, to adopt standard dimensions. Before about 1750, the size of instruments and their names differed from one country to another and from one luthier to another. Once the new standards had been established (namely the violin, viola and cello, which are still the current references), luthiers reduced instruments which stand between two sizes in order to make them fit a smaller size. An important question that arises in musicology nowadays is to determine whether or not an instrument has been reduced, and if so, to quantify how; this issue is also relevant for its cultural and economic aspects. A detailed historical review of violin reduction can be found in [CBF * 23,Zel19]. It should be noted that the reduction problem only concerns the sound box of the instruments, and not the neck, which has often been changed and replaced over time [Sib85, Sto90, Her03]. Figure 1: Impact of the reduction of the width of the sound box on the contour lines. Starting from the original instrument (left), a slice of wood is removed from the main axis (centre) and then the two halves are glued back together (right)

Affiliations

UCLouvainSST/ICTM/INMA - Pôle en ingénierie mathématique

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Beghin, P., Ceulemans, A.-E., & Glineur, F. (2025). DIGITAL HERITAGE (2025) Identification of Violin Reduction via Contour Lines Classification. Published. https://doi.org/10.2312/dh.20253083 (Original work published 2025)