In the present work a contribution to the study of the quantification of the radiation of the structure walls in systems of closed box has been made, establishing a relation of the vibroacustic response of this type of radiating systems with the characteristics of the material used, such as the Young modulus, the damping, or the density. From a general point of view, the object of the work fits within the problems of dynamic fluid-structure interaction, so the presented foundations of the procedures and models, are similar to the used in other dominions of application, like  the construction, aeronautics, naval construction, Biology, etc.   

In order to approach the problem, a mecano-acoustic couple between the different elements from the radiating system is considered. Ideally, in the radiating systems composed of loudspeakers mounted on an acoustic enclosure or box, the walls of the box are considerated infinitely rigid with null movement. In the reality, the experience demonstrates that the walls behave like vibrant plates under the action of the inner pressures, and contribute to the final radiation of sound of the system, mainly in the low frequencies range. To obtain the proposed objective, first a series of experimental measures has been made on models of closed box with and without loudspeaker. In the experimental procedure the vibracional behavior of the walls of the structure has been studied by means of modal analysis and measures of vibration. The acoustic response of the systems is evaluated by means of measures of acoustic pressure and intensity.   

Next, numerical models of the loudspeaker, inner air and structure have been implemented. The implemented numerical models are mechanical-acoustic, the electrical part of the loudspeaker has been replaced by a harmonic excitation force.   The first numerical model is three-dimensional, looking for obtaining a simulation of the simultaneous interaction of the three main elements of the system: the inner air of the box, the diaphragm of the loudspeaker, and the walls of the box. Moreover another numerical model in two dimensions has been implemented, adding the air outside of the box, and obtaining a fluid-structure-fluid couple. With both models a parametric study been made.
In sumary the structure colors the sonorous response of the system in all the studied frequency range, due to resonances or forced vibrations of the walls. On the other hand the proposed numerical model supposes an advance with respect to the presented ones until the moment. The model constitutes a design tool that allows to study in an economic form, the importance of the structure in the sonorous response of the system.