In the automotive industry, like in other transport industries, predicting noise during design cycle is a necessary step. Well-known methods exist to answer this issue in low frequency domain. Among these, Finite Element Methods, adapted to closed domains, are quite easy to implement whereas Boundary Element Methods are more adapted to infinite domains, but may induce singularity problems. In this article, a new method based on the well-known elastodynamics Substructure Deletion Method is presented. Analogies between acoustical and seismic problems are made to transpose the method. It consists in dividing a complex unbounded problem into two easier ones to solve finite and infinite problems. Instead of considering a geometrically complex structure, a prismatic bounding volume is first studied. Then a classical Finite Element computation is performed on the volume left between the box and the considered structure. The advantage of this technique is that when testing and comparing several geometries contained in such a box, only one boundary element calculation is needed. Efficiency of this method is discussed in the present document.