Computer modeling of the acoustic guitar

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Dr. Rucz Péter
Department of Networked Systems and Services

The design of the soundboard and the air cavity of a guitar are the most critical parts in terms of the sound quality of the instrument.

The string itself produces only a small amount of sound pressure because it has very low radiation efficiency. This phenomenon is called acoustic short-circuit. Hence, the soundboard must amplify the vibrational energy of the string. The top plate has a relatively large surface, which means that it can avoid the acoustic short-circuit and can radiate efficiently.

The air cavity also plays a very important role in the sound production, especially in the low frequency range.

This thesis shows the analysis of the aforementioned oscillating systems.

During the modal analysis of the soundboard the transfer characteristics were computed between several measurement points on a Fender CD-60 type folk-guitar top.

The measurement was based on the determination of the responses to excitations recorded by accelerometers. The force was generated by means of an impact hammer, which acted like a point source on the surface.

Therefore, the complex poles and the corresponding frequency values of the soundboard were determined.

The mode shapes of the air cavity were computed by means of numerical techniques in Matlab environment. With the utilization of the finite element method (FEM), a three-dimensional model was established.

After all, by using an alternative numerical method, the boundary element method (BEM), the outer infinite acoustic field was successfully coupled to the existing system.

Thus, a coupled simulation had been executed in a relatively wide bandwidth, in which the accuracy of the model was successfully tested by the evaluation of the transmission characteristics of the Fender CD-60.

The experiments and simulations presented herein in lead to a better understanding of the acoustics of the guitar and are helpful in the development of novel modelling techniques.


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