Temperature-dependent damping of the tonewood spruce

Abstract

The material wood is sustainable, resource- and energy-efficient and recyclable. Its low density which ranges between 0.5 and 0.8g/cm3 makes from it an important material in the transport sector, in which weight reduction is a key factor against the background of energy savings and the associated reduction in CO2 emissions. Wood can be regarded as a low-damping material, due to its molecular structure and its relatively high modulus of elasticity. This characteristic is well known to musical instrument makers. For musical instruments with a resonance body (e.g. piano, harpsichord, viola, cello, double bass, cymbal, harp, zither and certain organ pipes) spruce is the first choice of wood. Since the parameters time, temperature and moisture content influence the mechanical properties of wood, it is considered to be viscoelastic. Especially, the moisture content of the wood can significantly alter its sound quality and, thus, its damping behaviour. In order to study that moisture influence, the individual drying behaviour of nearly 130 years old spruce and new spruce wood was investigated by damping measurements as a function of the temperature. The material damping of new spruce wood was found to be generally higher than that of old spruce wood. Furthermore, former results showed that the damping of new wood is less sensitive to moisture content changes, which corresponds to a stable tone colour. Activation energies for damping mechanisms were calculated based on data from the Arrhenius plot of both woods. These results suggest that further or stronger damping mechanisms are active in new spruce wood.