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.

Reference

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

See also: Acoustic Tile, Articulation Class, Sound Transmission Class.

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Subjects: Noise & Vibration