The inclusion of CAC or STC in the ceiling panel specification does not result in higher vertical sound isolation from rooms above or below or greater attenuation of noise generated by mechanical equipment located in the plenum. Specification professionals can be confident that selecting ceiling panels with high sound absorption, as defined by an NRC rating of 0.90 or higher, will meet their projects’ acoustic performance requirements in accordance with building design standards and guidelines.
Notes
1 Examples include: the International WELL Building Institute’s WELL Building Standard, Sound Concept, Feature S02 Maximum Noise Levels; the Facilities Guidelines Institute’s “Guidelines for Design and Construction of Hospitals,” (FGI Guidelines for Hospitals) Table 1.2-5 Maximum Design Criteria for Noise in Interior Spaces Caused by Building Systems; and the American National Standards Institute and the Acoustical Society of America (ANSI/ASA S12.60), Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools, Part I: Permanent Schools, Table 1 Limits on A- and C-Weighted Sound Levels of Background Noise and Reverberation Times in Unoccupied Furnished Learning Space.
2 Refer to 2008 AHRI Standard 885 (with Addendum 1), Procedure for Estimating Occupied Space Sound Levels in the Application of Air Terminals and Air Outlets; free download at www.ahrinet.org/App_Content/ahri/files/STANDARDS/AHRI/AHRI_Standard_885_2008_with_Addendum_1.pdf; refer to Appendix D Sound Path Factors, Sections D1.6 Ceiling/Space Effect, Table D14 Uncorrected Ceiling/Space Effect Attenuation Values and Table D15 Ceiling/Space Effect Examples.
3 Review the 2019 ASHRAE handbook HVAC Applications, Chapter 49 Noise and Vibration Control; available for purchase at https://www.techstreet.com/ashrae/standards/a49-noise-and-vibration-control-si?product_id=2073870), Section 2.8, subsection Sound Transmission Through Ceilings and Table 43 Ceiling/Plenum/Room Attenuation in dB for Generic Ceiling in T-Bar Suspension Systems.
4 ASHRAE research project RP-755 was conducted by the National Research Council Canada (NRCC) and is available online at https://nrc-publications.canada.ca/eng/view/ft/?id=df153a91-863d-48ca-a037-dfbece1f5456.
5 More information about the ceiling panels in Table 1 can be found in ASHRAE’s final report RP-755, Tables 3-1 (page 6).
6 Refer to section 13 on pages 125-127 of ASHRAE RP-755 for the measured CAC and STC data and for more detailed analysis and discussion by the original researchers.
7 Examples include: the WELL Building Standard, Sound Concept, Feature S04 Reverberation Time and Feature S05 Sound Reducing Surfaces; FGI Guidelines for Hospitals, Table 1.2-4 Minimum Design Room-Average Sound Absorption Coefficients; and ANSI/ASA S12.60, Table 1 Limits on A- and C-Weighted Sound Levels of Background Noise and Reverberation Times in Unoccupied Furnished Learning Space.
8 Caution should be taken if the building design does not comply with minimum standards and has interior partitions that do not extend full height to the floor or roof above. In this case, a specifier might consider adding CAC back into the ceiling panel specification, so the CAC of the ceiling system equals the STC rating of the partition below the ceiling.
9 The background noise requirements provided in Step 2 are from the ASHRAE handbook, HVAC Applications (2019), Table 1 Design Guidelines for HVAC-Related Background Sound in Rooms. If the building must comply with a different building standard or guideline, use those values instead.
10 The values in this graph were derived using the method in the 2019 ASHRAE handbook HVAC Applications and 2008 AHRI Standard 885. Octave band values for the Noise Criterion curves taken from Table 13 in AHRI Standard 885 were added to the “Environmental Adjustment Factor” in Table C1 in AHRI Standard 885. The average “Uncorrected Ceiling/Space Effect Attenuation Values” per Table D14 in AHRI Standard 885 were added to the sum to get the maximum permissible sound power levels for the mechanical equipment in the plenum.
Author
Gary Madaras, PhD, is an acoustics specialist at Rockfon. He helps designers and specifiers learn the optimized acoustics design approach and apply it correctly to their projects. He is a member of the Acoustical Society of America (ASA), the Canadian Acoustical Association (CAA), and the Institute of Noise Control Engineering (INCE). Madaras can be reached at gary.madaras@rockfon.com.
