A Comparative Study between the Traditional Ratings and Real Acoustical Properties of Walnut Wood (Juglans regia) used in Santur Making*
For many years، the wood of walnut tree (Juglans regia) has been used for making Santur. Even though artisans have their own divers’ ideas about this species’ features; until now there has been no scientific data to support them. In Santur’s case specially، differently cut surface plates can be formed into final instrument. Besides، some steam treatments، which supposedly improve the final sound quality، are common for preparing the raw material. Their true efficiency is also unknown. In this study، specimens from Sanoor’s surface plates with different traditional grading were collected from ateliers of two professional instrument makers and their real vibrational properties were measured and compared. Different cutting plans، visual characteristics، the types of pretreatments involved as well as the sample’s age and conditions were the basis of grading according to artisans. Samples were dried and stabilized in a climatic chamber before being tested for their vibrational qualities. The vibration test was done using a non contact free-free bar bending method. The frequency sweep was between 100 and 500 Hz and both specific elastic modulus (E/ρ) – from the first frequency resonance using Euler-Bernoulli method– and damping coefficient (tanδ) –using bandwidth at the half power– were calculated. Walnut wood had the basic characteristics of chordophones related species: high specific modulus and comparatively low damping coefficient. No statistically significant difference was observed between the four obtained mechanical factors (i. e. Density، Young modulus، specific modulus and damping) based on the wood conditions (Heartwood or sapwood). However the traditional grading was related to the measured characteristics. The best graded specimens had both higher densities and Young moduli. In all specimens the standard decreasing relation between damping coefficient and specific modulus was observed. This verified the trustworthiness of the calculated data. As a general fact، the results of acoustical tests were in harmony with the grading. This means that the better graded samples had relatively higher specific moduli and lower damping coefficients. The situation was vice versa for the lowest grades. The line separating the best and the worst graded specimens was very clear، on the other hand middle range grades borderlines were vague، meaning all the measured factors were almost in the same range. This indicated the importance of artisanal cut، wood color and design in traditional grading: one acoustically valuable specimen could be cast aside just because it is not properly cut. Steaming as a commonly done traditional pretreatment had improving effects on the wood’s final characteristics: it apparently caused the specimen properties to get closer to the best graded ones. An old wood can also be considered a treated specimen، as aging can also be done artificially (by the hands of the craftsmen through leaving the wood untouched for years before beginning the process of fabrication) or naturally (as in direct using of an old tree). Walnut aged specimen، also demonstrated nearly the best mechanical features، validating the choice of the instrument makers in preferring the aged wood over the freshly cut one. In conclusion، in the case of Santur، a significant coherence between artisanal experimental knowledge and scientific data was observed
Honar-Ha-Ye-Ziba: Honar-Ha-Ye Mosighi Va Namayeshi, No. 47, 2013
23 - 32
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