In this article, the performance of a two degree-of-freedom dynamic vibration absorber (DVA) with very large or very small moment of inertia is studied. Although it has been shown previously that an optimally tuned DVA with a negligibly small moment of inertia marginally outperforms the optimally tuned DVA with a very large moment of inertia, the physical reasons for this have not been made clear. Using a simplified model of the stiffness elements of the DVA, it is shown that the two sets of parallel combinations of stiffness and damping elements of the DVA with negligibly small moments of inertia effectively act in series, rather than in parallel as in the other case. Furthermore, it is shown that the stiffness and damping elements can be represented as a single stiffness and a single damping element whose properties are frequency dependent. This frequency dependency means that there is additional freedom in choosing the optimum stiffness and damping of the DVA, which results in better performance.