One of the main goals of the research in Molecular Magnetism is to increase the blocking temperature TB of Single-Molecule Magnets (SMMs). A significant breakthrough was achieved with the dysprosocenium compound and its record TB = 60 K. Recent results on similar Dy-based compounds showed a clear correlation between TB and Raman relaxation. Thus, a deeper insight into SMMs phonon-induced relaxation dynamics is required, but very few experimental information on phonons is available. Having already successfully measured the phonon density of states (DOS) of the dysprosocenium compound, we propose using MERLIN to measure the phonon DOS of two other Dy-based molecules, displaying much lower TB despite still having strong magnetic anisotropy. This systematic study on phonons in SMMs will allow us to correlate them with TB, in order to identify the real ingredients behind high-TB compounds.