Optimizing Ceiling Systems and Lightweight Plenum Barriers to Achieve Ceiling Attenuation Class (CAC) Ratings of 40, 45 and 50 Points

Acoustics is one of the lowest scoring indoor environmental quality metrics in building occupant surveys. This is in part due to the misconception that a lightweight, modular, acoustic ceiling alone can be used to block noise when room demising walls do not extent full height. Acoustic codes, standards and guidelines typically require 40, 45 or 50 decibels of isolation between rooms, yet most ceiling panels only provide 20-35 decibels of inter-room blocking. Penetrations for lights, grilles and diffusers can decrease the ceiling attenuation class (CAC) by 10 decibels overall and 20 decibels in the 1,000, 2,000 and 4,000 hertz octaves. A full height wall is the preferred way to block inter-room noise, but when combined with the 20-25 decibels of blocking provided by typical ceiling systems that have been penetrated by lighting and air distribution systems, can result in unnecessary costs to the project. The isolation provided by the ceiling and upper wall significantly exceeds that provided by the lower wall. Laboratory tests were conducted to optimize combinations of modular, acoustic ceilings and lightweight top of wall, plenum barriers that result in ceiling attenuation class ratings of 40, 45 and 50 points. The ceiling systems and the plenum barriers contained multiple penetrations for building services, representing real world application.