During the last decades, new building techniques based on lightweight systems have been developed and today they are frequently used in many countries. Nowadays, these systems present some disadvantages when compared with the traditional building technologies, since most of the acoustic regulations are still based on the latter. Frequently, the acoustic rating of a lightweight structure using the standard methods is not well correlated with the perceived disturbances caused by footsteps, falling masses, etc. Wooden houses are specifically known for their poor impact sound insulation, fulfilling the legal requirements but highly annoying for the residents. Therefore, the intention of this paper is to contribute to a better knowledge of the vibrational behavior of lightweight wooden floors (LWF). In this study, a simple un-damped floor with constant cross-section geometry and elastic properties along one of the coordinate axes has been selected. These kinds of structures can be considered as waveguides where the cross-sectional modes are propagated as waves along one axis. The dispersion curves describe the wave propagation in the structure where each curve represents one wave. This approach is very helpful to facilitate the physical understanding of the acoustical performance of the floors since each wave present in the structure can be identified and classified. The so-called Waveguide Finite Element Method (WFEM) has been applied. This method uses finite element techniques to describe the modes of the cross-section geometry. Each mode is then propagated along the waveguide, getting the wave solutions or dispersion curves. To understand the wave propagation on the structure, different modifications of the LWF have been analyzed. In these modifications, the different basic parts of the floor (beams and plates) have been decoupled to different degrees by e.g. blocking degrees of freedom or changing the elastic parameters of the coupling elements. This methodology allowed for analyzing the evolution of the vibrational behavior of the system from the uncoupled waveguides to the complete coupled structure, getting a full picture of the vibrational behavior of a LWF.