Experimental and theoretical studies of the modes of stringed instruments and their relevance for quality control of instrument manufacture

Abstract

This paper reviews various methods for measuring and predicting the modes of vibration of the wooden structures found in instruments of the violin and guitar family. These methods include holographic and speckle interferometry, modal analysis by impact hammer excitation, and the finite element method. Theoretical modeling of stringed instruments has now advanced to the stage where the models can be ‘‘played,’’ allowing listening tests to be used to link construction of the instrument with the perceived sound quality in a formal way. Early indications of this work suggest that mode frequencies play a much smaller role in determining the sound quality of an instrument than has previously been assumed, and that greater attention should be paid to the ‘‘ease’’ with which modes can be driven by the strings and to the ‘‘source strengths’’ of the modes. This paper will put the case for measuring additional modal parameters, such as effective mass and effective stiffness, and discuss their relevance to quality control by the maker during manufacture of an instrument.