Ceiling Attenuation Class
This is a rating value for the efficiency of the ceiling as a barrier to airborne sound transmission between adjacent rooms when the dividing wall doesn′t connect with the structural ceiling.
The ceiling plenum is the volume defined by the area above the back of the ceiling tile, and below the bottom of the structural slab above. Within this plenum is usually found a combination of HVAC ducts, electrical and electronic conduits, water pipes and other items such as loudspeakers to delivery masking noise.
35 is a typical CAC for offices.
A ceiling system with a CAC < 25 is consider low performance, whereas one with CAC > 35 is high performance.
ASTM E1007 Field Measurement of Tapping Machine Impact Sound Transmission through Floor-Ceiling Assemblies and Associated Support Structures
ASTM E1111 Measuring the Interzone Attenuation of Ceiling Systems
ASTM E1414 Airborne Sound Attenuation Between Rooms Sharing a Common Ceiling Plenum
ISO 140, Part 9 Laboratory Measurement of Room-to-Room Airborne Sound Insulation of a Suspended Ceiling with a Plenum Above
Subjects: Noise & Vibration