Material variability compensation in a finite element model of a classical guitar by appropriate geometry modifications

Abstract

The sound of some old master instruments like the Stradivari violins or the Torres guitars is still unrivaled for many musicians. The common practice among instrument makers is to copy these instruments by building instruments with the same geometry as the original. However, audible differences between these copies and the original instruments are unavoidable, mainly due to the natural variability of the wood characteristics. A suitable measure to objectively characterize an instrument's sound is evaluating its modal parameters. Our project aims to develop a methodology to design copies of the old master instruments that match these modal parameters of the original instruments instead of copying their geometry. After showing that such an approach is appropriate for an individual guitar soundboard in a recent publication, we now present a parameter study to find suitable geometric modifications on an entire guitar to compensate for the natural material variation. Therefore, this study is based on a detailed finite-element model that shall predict the effect of suitable geometry alterations on the instrument's modal parameters and suited optimization techniques. Geometric modifications like the shape of the braces, the thickness of the fretboard, and the thickness of the plates are taken into account.