The traditional one-dimensional mechanical models of longitudinal or transverse vibrations of beams in the acoustic field considers material in vibration as being elastic and homogeneous. The use of these models leads to the expression of the deformation, as well as the Eigen frequencies of vibrations, by the use of the equation of the movement and the boundary conditions. For the technologist working in pure elasticity, the spectrum is then reduced to a succession of infinitely long vertical bars whose X-coordinates correspond to the values of the Eigen frequencies. However in physical reality, the frequency spectra obtained in experiments are very far from resembling a purely elastic modelling which thus remains very restrictive. To use the traditional developments in dynamics of the beams in the purely elastic field thus allows only one very limited comprehension of the phenomena occurring in material when this one is in vibration. Decades ago, the data processing specialists in musical synthesis developed new musical instruments very different from those usually manufactured in stringed-instrument trade made up primarily of printed circuits. The technologist and the data processing specialist in musical synthesis tackle the same physical problem under two different and complementary aspects. It is indeed possible to unify the models of musical synthesis and the models of mechanics of materials. This study allows a characterisation of wood material in longitudinal vibration from the point of view of its elasticity but also of its viscosity starting from an impulse dynamic test. The whole of the phenomena, such as the delay, dispersion, and the dissipation, which transform the waves during their propagation are taken into account through specific mathematical formulations. In addition, tests of total characterisation of beams coming from historic buildings, from the elastic and viscoelastic point of view, show the interest of this method for the mechanical classif