There are two important acoustic parameters for a suspended ceiling system, sound absorption and the ceiling attenuation class (CAC). The sound absorption of a suspended ceiling system indicates how much of the incident sound is absorbed, whereas the CFN indicates how much sound is transmitted between two adjacent rooms, through the suspended ceiling system and plenum. The random sound absorption coefficient will be determined using a reverberation room for the front face (the side which faces the room), and the back face (faces into the ceiling plenum) for each ceiling tile product studied. A CFN facility complying with ASTM E1414-11a was commissioned, and consequently used to determine the transmission loss through the plenum sound path (transmission loss from one room through a suspended ceiling system, across the common ceiling plenum, and down through a suspended ceiling system into the adjacent room) of five ceiling tiles. It was found that as the mass of the ceiling tile increased, the transmission loss increased. This was also seen when acoustic absorption was added to the rear of the ceiling tiles in the plenum. As the mass of the ceiling tile / acoustic absorption increased, the transmission loss increased as per mass law (6 dB increase per doubling of mass).