Finite element modelling of Japanese koto strings

Abstract

The development of a high resolution finite element model of the Japanese koto has been previously reported. The koto is a plucked zither made of paulownia wood and 1.83m in length. Its 13 strings are made of polyester fibre and supported by 13 moveable bridges approximately 6cm high. A functional representation of each string was included in the high resolution model by using a wave form that entered the koto sounding body at a signal point where the bridge would be located for the standard (hirajoshi) tuning. Correlation between spectra generated in the model and spectra of an actual instrument as played provided initial observations of string behaviour. This study aims to improve the fidelity of the spectral response by directly coupling the string resonating body. A beam model and a truss model with the dimensions of a professional string that is pre-tensioned to yield a close approximation of strings on an actual instrument are studied. Initial results from the string models as compared to notes played on the koto used as the basis of the finite element modelling are reported.