Measurements of Acoustic Radiation of Tonewood Spruce at Different Clamping Loads

Abstract

The usage of wood as an environmentally friendly material combines optimized room aesthetics with mechanical and/or acoustic functionality. Cellular materials like wood play an important role in reducing vibration and noise. It is considered to have low damping properties due to its molecular structure and its relatively high modulus of elasticity. This property is well known to musical instrument makers and is accordingly taken into consideration in the manufacture of such instruments. Site-specific, targeted wooden cladding can help to dampen vibrations. Against the background of noise and vibration control, wooden plates in the form of connected bodies are often used, e.g. to build an enclosure. The vibration behaviour of the resonance body of a wooden musical instrument is difficult to determine. In this context, basic acoustic investigations into the radiation efficiency of wooden panels become mandatory. The solutions to the equation of motion of the vibrating plate depend, among others, on the geometry of the plate and the conditions of its clamping. A fact that makes it very challenging to predict is e.g. eccentric load application that causes much more natural vibrations. In this paper, a plate made of the tonewood spruce was mechanically excited in the centre on the back. The acoustic intensity of the panel on the other side was then measured as a spatial function using an acoustic sensor. Since the clamping conditions influence the vibration characteristics, the measurements were conducted under different clamping loads. A relatively stable mode pattern emerged that was more pronounced at the highest clamping load.