In this case, the emitting and the receiving rooms are horizontally separated by an already existing pavement which is
formed by four layers and as follows (from the bottom to the top): a 0.1 cm painting layer (1, Fig. 4b); a 45 cm thick reinforced concrete slab (2, Fig. 4b);. a 3 cm thick light weight concrete regularization layer (3, Fig. 4b) and a 0.3 cm thick polymer based material top finishing (4, Fig. 4b).