Two classrooms of a building located in the university of Trásos-Montes e Alto Douro campus, in Vila Real city, Portugal, were adopted as emitting and receiving rooms. Both rooms are geometrically similar and have the layout shown in Fig. 2. One room is superjacent (i.e. the emitting room which is located on the second floor) to the other (i.e. the receiving room which is located on the first floor). There is a road next to the building and, therefore, the sound resulting from the traffic had to be taken into account in this evaluation. The tests were performed in July 2011, when the semester had already ended and there were no classes.