Résumé
Woods, as the constitutive materials of a majority of musical instruments throughout the world, play a major role in their final behaviour and "cultural/musical identity". Musical instrument making, which can be considered as an "intangible cultural heritage", involves the acquisition and transmission of very specific craftsmanship skills, and is integrated into a wider context - woodworking and musical traditions of a given geo-cultural area, but also knowledge on woody plant resource and material. The choice of wood by instrument makers is an essential part of such traditional knowledge and know-how. Due to the "ambivalent" nature of musical instruments (with equally strong acoustical/mechanical, and cultural, functions), the woods chosen for their building have been studied -for nearly a century now- from two distinct points of view/disciplines: "engineering" and "ethno-botanical" points of view. This paper aims at illustrating some wood science approaches to musical instrument making, with particular focus on the links between mechanical/acoustical and traditional/empirical criteria of material selection. It relies on a survey of existing literature, combined with our personal works: characterization of dynamic mechanical and physical properties of instrument woods, interviews with instrument makers, and inter-disciplinary database construction. It considers two case studies (woods for top-plates of stringed instruments and woods for bows) and two levels of variability: chosen species in different cultural contexts, and within-species wood piece selection by makers. Between-species diversity results suggest that: (i) the "western classical music instruments" standard which is usually used in material research studies cannot always be extrapolated to other geo-cultural areas; (ii) the amount of diversity in chosen species results from the combination of material availability, of mechanical "performance", but also of musical/technological trends related to a cultural context. Such trends continuously evolved since the Middle-Ages in the case of European bows, resulting in some "diversification" and some "standardization" epochs. Within-species selection by makers is by essence based on multi-criteria approaches. Different works on psycho-sensorial classification of woods for string instruments tend towards the same conclusions in terms of material properties, but they do not always fully converge, due to the "human variability" parameter, which suggests that wider samplings and surveys with several makers would be useful. The analysis of the relation between mechanical assessment and "empirical" classification of different "qualities" of pernambuco wood for modern violin bows, through two recently published references plus our present work; suggests that: (i) specific gravity and Young's modulus are indeed important parameters in bow material selection, but not always sufficient for discrimination of empirical qualities; (ii) taking into account, not only density and elastic properties, but simultaneously colorimetric (CIELCh) and dynamic mechanical (loss coefficient tanδ) parameters allowed for a much clearer discrimination between "traditional knowledge" classifications, which highlights the importance of multi-criteria, and multi-disciplinary approaches, if a better global understanding of traditional knowledge is sought after.