Fluid-structure coupling in the guitar box: numerical and experimental comparative study

Resonance boxes are common to many musical instruments and determine the radiated sound to a great extent. The behaviour of the structure and the air inside must be understood as a whole, the complexity of which is increased by the presence of sound holes. In this work, we present a comparative study of the guitar box in which the interior gas is changed both experimentally and numerically. Modal patterns, natural frequencies and quality factors are determined when the box is full of helium, air and krypton, respectively. This allows us to characterise the soundboard-back plate coupling via the cavity fluid, stressing the role of the structural and acoustic uncoupled modes. This could help guitar makers, allowing them to modify the final modes by means of structural modifications. Moreover the methodology, together with the developed finite element model, proves to be valid for studying the dynamic fluid-structure coupling in any arbitrary mechanical system, including cavities connected to the surrounding air.