The classical guitar is a popular string instrument in which the sound results from a coupled mechanical process. The oscillation of the plucked strings is transferred through the bridge to the body, which acts as an amplifier to radiate the sound. In this contribution, a procedure to create a numerical finite element (FE) model of a classical guitar with the help of experimental data is presented. The geometry of the guitar is reverse-engineered from computed tomography scans to a very high level of detail, and care is taken in including all necessary physical influences. All of the five different types of wood used in the guitar are modeled with their corresponding orthotropic material characteristics, and the fluid-structure interaction between the guitar body and the enclosed air is taken into account by discretizing the air volume inside the guitar with FEs in addition to the discretization of the structural parts. Besides the numerical model, an experimental setup is proposed to identify the modal parameters of a guitar. The procedure concludes with determining reasonable material properties for the numerical model using experimental data. The quality of the resulting model is demonstrated by comparing the numerically calculated and experimentally identified modal parameters.
In this article, the transient motion of a realistically plucked guitar string is studied experimentally and numerically in both transversal polarizations. The frequency dependent damping and suitable initial conditions are identified in the experiment and used in a simulation. For this reason an experimental set-up consisting of a string, an excitation mechanism and two laser Doppler vibrometers is developed. The excitation mechanism performs a realistic and reproducible plucking motion with a plectrum. Two laser Doppler vibrometers are used to measure the string oscillation transversally in two polarizations. The experimental set-up makes it possible to measure the string’s motion under reproducible conditions and, hence, at different positions for the same oscillation. This capability renders the identification of suitable initial conditions, i.e., initial displacement and velocity as well as the pre-tension, for a string model possible. Furthermore, a finite element model for the string is developed that takes into account the oscillation in both transversal planes of polarization and the coupling between them. Finally, the model results are in good agreement with the measurements. With help of the numerical model it can be vividly shown that the coupling between the polarizations of the oscillation is due to a torsional movement of the string on the saddle.
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