High-CAC Ceilings
What you need to know
Ceiling Attenuation Class (CAC):
What’s CAC? CAC is a measure for rating the performance of a ceiling system as a barrier
to airborne sound transmission through a common plenum between adjacent closed spaces
such as offices.
• The higher the CAC rating, the better the performance. A ceiling system with a CAC < 25
is very low performance, 25 - 35 is better but still not the “best choice.” CAC > 40 is high
performance.
• When using a high-CAC ceiling, wall construction with a minimum STC 40 rating should
be specified.
Balanced Acoustical Design:
You can Block noise with an effective combination of wall and ceiling construction,
using a high performance CAC ceiling.
Other considerations affecting ability to effectively block sound:
– Door and window seals
– Wall/floor interface
– Wall system joints
– Air returns
– Penetration in light fixtures
CAC is measured according to ASTM E1414
Application Considerations:
CAC is important between closed spaces and from closed rooms to adjacent spaces,
such as corridors:
– Closed office, conference rooms
– Classrooms / core learning areas
– Mixed Plan Offices
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Other resources available:
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• Website www.armstrong.com/acoustics
• CS-3832 Marshall Erdman case study
• CS-3513 HIPAA/Speech Privacy white paper
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• CS-3712 Office Acoustics white paper
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• CS-4556 Sound Design™ brochure
ARMSTRONG PRODUCT FAMILIES OFFERING HIGH-CAC
– MetalWorks™ (unperforated)– Ceramaguard®
– Ultima®
–
Cirrus®
– Mesa™
– School Zone™ Fine Fissured™
CEILING
SYSTEMS
Between us, ideas become reality ™
– Ceramaguard Fine Fissured™
– Clean Room™ VL
– Cortega®
Construction Practices and
Creating Effective Speech Privacy
Effective Building Design:
Building design can have significant impact on speech privacy and construction costs.
Below are typical construction scenarios showing how speech privacy is affected.
Standard Performance
Scenario 1:
Scenario 2:
Ceiling panel (NRC 0.50/CAC 33) with
no plenum barrier
1.5” Fiberglass board fitting
around plenum obstructions, and
a ceiling panel (NRC 0.50/CAC 33)
Privacy Index = 90% Non-intrusive
Privacy
Privacy Index = 95% Confidential
Privacy
Concrete Deck
Concrete Deck
Plenum
Plenum
Ceiling
CAC 33
Ceiling
CAC 33
Wall w/R11
STC = 44
Wall w/R11
STC = 44
Best Performance
Scenario 3:
Scenario 4:
Walls to deck. 5/8” Drywall fitting
around plenum obstructions, and a
Ceiling panel (NRC 0.70/CAC 40)
ceiling panel (NRC 0.50/CAC 33)
Privacy Index = 98% Confidential
Privacy
Privacy Index = 97% Confidential
Privacy
Concrete Deck
Plenum
Wall STC + 38
Ceiling
CAC 33
TechLineSM / 1 877 Armstrong
1 877 276 7876
armstrong.com (search: acoustics)
BPCS-3845-313
Plenum
Ceiling
CAC 40
Wall w/R11
STC = 44
NOTE: RC 30 background noise
Concrete Deck
Wall w/R11
STC = 44