The resolution of electrical circuits and its acoustic homologous from a physical point of view is presented here. Based on the structural analogy with a mechanical system in equilibrium, it is possible to associate a Lagrangian depending on the generalized forces in a viscous medium with friction coefficients and with a set of holonomic constraint functions. By means of the Hamilton principle applied to this Lagrangian associated with a circuit, an equation of a function of a set of independent variables can be obtained, which turns out to be the condition for the resolution of a typical problem of linear programming. This minimized expression represents, in turn, the power dissipation. From all the possible values that could take a set of speed and pressure, the principle picks out one and only one (the true values) with the condition of producing the least power dissipation. All acoustic devices or systems that could be represented by an electric circuit may be solved by this method with the physical meaning described here.

Microperforated panels have been studied as a good, interesting absorbing element. In previous papers the properties of high absorption obtained in a wide frequency band was demonstrated, based on the impedance of the very small perforations. The perforation area ratio, the diameter of the holes, the thickness of the panel, and the density and viscosity of the air are the terms that define the sound absorption provided by the element. The microperforated panels have a simple structure and it is possible to build single or double resonators, in order to obtain a wide band response. An orifice may be considered as a short tube. Many years ago, Rayleigh and Crandall studied the propagation of sound in small tubes, of a very short length compared to wavelength. They found a high acoustics resistance and a very small reactance. So, the microperforated panel can be used as a dissipative element. An experimental investigation was carried out on different samples of microperforated panels, in order to obtain their sound absorption coefficient and so verify the validity of the mathematical models. Microperforated panels have been developed to cover a welding cabin internally, where classical absorbents are useless. (To be presented in Spanish.)