Performance comparison of above ceiling and through ceiling sound masking systems

Sound masking systems are an important tool for providing speech privacy in offices and similar spaces. These systems typically use an array of loudspeakers radiating masking sound above an acoustical tile ceiling. The ceiling acts to diffuse the sound laterally in order to minimize localization on loudspeakers by the listeners below. The diffusion also helps keep the speech‐to‐noise ratio relatively uniform spatially, which may help minimize variations in privacy conditions. Unfortunately, the ceiling material, the plenum, and the space below are rarely homogeneous acoustically. There are usually openings in the ceiling for HVAC return air and lighting fixture ventilation, and different parts of the ceiling often use a variety of materials and elevations for aesthetic reasons. Large ducts and structural elements may compartmentalize the plenum. These variations pose substantial acoustical challenges for the designer and additional costs for the owner, not all of which can be satisfactorily resolved. Reco...