Coupled modes of the resonance box of the guitar

Abstract

Vibrations of the resonance box of the guitar have been studied by means of the modal analysis technique and the finite-element method. An expert craftsman constructed the guitar box with all the structures, internal and external, characteristic of a real instrument for the experimental measurements. The boundary conditions were chosen in order to clarify the soundboard-back interaction only via the internal air coupling. The numerical model allows one to study the influence of each component on the whole box, and the contribution of the modes of the components (wooden box and its parts, and air), to the coupled modes by calculating their participation factors. The coupled modes of the guitar box are discussed taking into account both the finite-element and modal analysis results.

Fluid–structure coupling in the guitar box: numerical and experimental comparative study

“…As was demonstrated in a previous paper [8], the air contained in the box provides a coupling between the soundboard and back plate, giving rise to the box modes. Moreover it acts as an added mass because the natural frequencies decrease in comparison with those of the structural modes.…”

“…The numerical model used to model the resonance box is based on the finite element method, and is described in previous articles [8,12]. In summary, a guitar box model (whose geometrical design and material parameters were similar to the real one) was assembled from its individual components.…”

“…The experimental device along with the guitar box description has been published elsewhere [8,11]. In this case the modal analysis technique has been applied to the resonance box when filled with helium, krypton and air (this last case was previously described separately [8]) in order to compare their respective effects on the dynamical behaviour. Among the available approaches, the measurement of the frequency response function (FRF) was chosen.…”

“…The vibrational dynamic was studied at every constructional step, determining the evolution of the modal parameters. The structural modes corresponding to the box (the empty wooden structure) with the ribs fixed can be found in [8] and are shown schematically in Fig. 1.…”

“…In previous studies, we have investigated the vibrational dynamics of the guitar box by means of experimental measurements and numerical calculation [8]. The aim of the present paper is to examine in detail the way in which structural modes couple with fluid modes in the low-frequency range (up to 400 Hz).…”