Protection against dangerous and harmful vibration is an urgent problem all around the world. Considerable efforts are in progress for researching and developing acoustic metamaterials. One of these acoustic materials’ working principles is the mass-in-mass subsystem that is an improved version of the 2-degree-of Freedom system of dynamic reduction of vibration. The main goal of this paper is to introduce the actualities of practical research work on this field of the University of Szeged, Faculty of Engineering. First a short review of the theory is summarized, presenting effective mass, differences between linear and non-linear spring characteristics, results of rotating vector solution. The paper highlights the author’s theory of the 5-degree-of-freedom subsystem of the “wall-paper”—like acoustic material. Then it shows the research instruments with the experimental system. It reveals the gap between the theory and the research results and features the present problems of the research, bringing into focus the practical side of it. It shortly introduces the used simulation software that reduces the number of the experiments. The other goal of this paper is to display the present state of the author’s last year began PhD work and the planned further steps.