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FEATURE
| acoustics
desired, consider perforated or slotted ceiling systems made from metal or wood. Most of these systems offer a variety of finishes and perforation patterns. To achieve an NRC rating of 0.90 or higher, a more open perforation pattern of 5% to 10% or more, and the use of a fibrous batt on the topside will most likely be required. If fiber erosion is a concern, some manufacturers offer encapsulated fibrous batts. Should a ceiling not fit with a project’s desired aesthetic, know that an equal amount of absorption can be achieved with a variety of acoustic metal decks, spray-on deck treatments, suspended horizontally oriented clouds or islands, or vertically oriented baffles. The first step is to determine how many Sabins of absorption a ceiling with NRC 0.90 would have provided if it would have been used. For every 10 sq. ft. of open-office space, an NRC 0.90 ceiling would provide 9 Sabins of absorption. Another way to look at is to multiply the area of the open office by 0.9 Sabins/sq. ft. to determine the total number of Sabins required by any other solution. Example: A 2,500-sq.-ft. open-office area should have 2,250 Sabins of absorption over it. (2,500 sq. ft. x NRC 0.90 = 2,250 Sabins) The amount of sound absorption provided by acoustic products and materials varies by frequency. Therefore, the number of Sabins varies by frequency as well. Ideally, the acoustic solution used should provide the calculated
Should a ceiling not fit with a project’s desired aesthetic, know that an equal amount of absorption can be achieved with a variety of other treatments and devices.
total number of Sabins at all frequencies. In reality, it becomes increasingly difficult to meet this ideal absorption goal for frequencies below 500 Hz.
offices to achieve an acceptable level of speech privacy,
Gary Madaras, PhD, ASA, INCE, Assoc. AIA, is the
Try to reach this ideal goal at 500 Hz and above. It might
there are numerous design options ranging in aesthetics
acoustics specialist at Rockfon North America, Chica-
be necessary to accept a lower amount of absorption
and budget. With so many choices, the acoustics can, in
go, where he helps designers and specifiers learn the
below 500 Hz unless commercially available, specialty
fact, be the creative inspiration for the space. Also
Optimized Acoustics design approach. Madaras is a
low-frequency absorbers are incorporated into the
remember that an NRC 0.90 ceiling over an open office
member of the Acoustical Society of America (ASA),
design. This is seldom done because the most common
space is only one of at least five requirements needed to
the Canadian Acoustical Association (CAA), and the
and distracting noises inside open offices areas occur at
make a space successful. No single aspect alone guaran-
Institute of Noise Control Engineering (INCE). He can
500 Hz and higher.
tees acoustic success. CA
be reached at gary.madaras@rockfon.com.
Consider combining systems if no single approach provides all of the necessary absorption. For example, perhaps an array of vertically suspended acoustic baffles is desired visually, but too many baffles in too tight of an array are required. Instead, consider using an aesthetically pleasing baffle array and accomplish the additional absorption by using a lower-performing acoustic-metal deck above them or apply a treatment to the underside of
PODCAST Learn about an acoustics ROI calculator designed for office spaces in a new podcast editorial director Gary L. Parr recorded with Gary Madaras, author of this article, and Shirley Wodynski, executive director of the Ceilings & Interior Systems Construction Association (CISCA), Oak Brook, IL (cisca.org). Listen to the podcast at commercialarchitecturemagazine.com/1903facousticpod.
the deck. Often, the best acoustic experiences are a result of using a variety of materials, each with their own acoustic advantages, arranged at different heights and orienta-
ADDITIONAL RESOURCES
tions. There is no need to become overly concerned with
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heights and spacing. The most critical design aspect is the total amount of absorption. Try to distribute it somewhat uniformly over the entire open-office area.
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Architects and specifiers should not feel limited by the acoustic requirements of the spaces they are designing. While it is has been known for decades that treatments of NRC 0.90 or higher are required over open 22
MAY 2019
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“Acoustic Design Guide for Open Offices,” Warnock, A.C.C., National Research Council Canada report IRCRR-163, March 2004. “Measurements of Sound Propagation between Mock-Up Workstations,” Bradely, J.S., Wang, C., National Research Council Canada report IRC-RR-145, January 2001. “Acoustical Design of Conventional Open Plan Offices,” Bradley, J.S., National Research Council
Canada report NRCC-46399, June, 2003.
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“A Renewed Look at Open Office Acoustical Design,” Bradley, J.S. National Research Council Canada report NRCC-46399, August, 2003.
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“Acoustical Design for Open-Plan Offices,” Bradley, J.S., National Research Council Canada construction update no. 63, October, 2004.
