Dynamic Response Optimization of an Acoustic Guitar

Abstract

Currently the production process of acoustic guitar factories does not result in instruments with equal dynamical behaviour, due to the varying material properties of wood from tree to tree. Experienced individual guitar builders are able to handle those material variations, but this is a labour intensive process because there is no structured methodology available about how to obtain a certain desired frequency response. In this study it is investigated if the perceived sound produced by a guitar is controllable by using dynamic response optimization methods in order to adjust geometric design parameters during the production process. The goal is to find a method which is both able to improve the consistency between mass-produced instruments and to decrease the required building time of handbuilt guitars. Until now no research is available which uses optimization methods in order to shape the dynamic response of a guitar over a range of frequencies. Previous research presented an analytical model which is able to give a quantitative description of a guitar’s dynamic response. The response is characterized by a measurement of the sound pressure level at 1 meter distance over a range of excitation frequencies. It was shown that the sound of a guitar is mainly determined by the dynamic behaviour of its top plate. This study uses a finite element model in order to estimate the effect of geometric design variations. The finite element model is used in combination with an optimization algorithm which shapes the dynamic response to a certain desired response. Due to this optimization approach the finite element model needs to be evaluated for many combinations of design variables. A computationally cheap finite element model is needed to approximate the physical behaviour of the guitar’s top plate. Based on the results of the optimization algorithm it is concluded that it is indeed possible to control the perceived sound produced by a guitar, by using dynamic response optimization methods in order to adjust geometric design parameters during the production process. Although some aspects need to be worked out further before the approach presented in this research can be implemented in a production process, the theoretical background will definitely be useful in order to improve consistency between instruments by using frequency response measurements during the building process.