Improved well-being
In 2003, a multiorganizational study conducted by academic institutions in the United States and Sweden inside a Swedish hospital investigated the effect high-performance, sound-absorptive ceiling panels had on the quality of care and physiological state of patients in an intensive coronary care unit (ICCU) (See Influence of Intensive Coronary Care Acoustics on the Quality of Care and Physiological State of Patients by Inger Hagerman et al.). The study was conducted in an actual hospital ICCU under clinical conditions and involved 94 coronary patients.
During the 20-week baseline condition, the ceiling was hard and sound-reflective. Patient physiology (heart rate and variability, blood pressure, pulse, etc.) and acoustic conditions (RT) were recorded. At the end of the baseline condition, the ceilings in the ICCU were changed to high-performing, Class A, acoustic ceiling panels. Class A in Europe is equivalent to NRC 0.90 in the United States.
Patient physiology and acoustic conditions were then monitored for another 22-week period. The study showed the effects of the high-performing, acoustic ceiling panels decreased patient heart pulse amplitude and their rehospitalization rate. In other words, the high-performance ceiling panels reduced stress in the patients’ bodies and cardiovascular systems, while they were in the hospital, resulting in fewer of them being readmitted after three months due to complications or reoccurrence.
In 2010, researchers from the Department of Psychology at the University of Kaiserslautern in Germany studied the effect of RT and noise on speech perception and listening comprehension in child and adult students (Read Effects of Noise and Reverberation on Speech Perception and Listening Comprehension of Children and Adults in a Classroom-Like Setting by Maria Klatte, Thomas Lachmann, and Markus Meis, 2010.). Acoustics conditions in a real classroom, before and after an acoustic renovation, were measured and then simulated in the laboratory of the university’s Hearing Research Center.
The acoustically unfavorable condition, representing surfaces with low sound absorption performance, had an RT of 1.10 seconds. The acoustically favorable room, representing surfaces with high-performing sound absorption, had an RT of 0.47 seconds (as mentioned, ANSI/ASA S12.60 recommends classrooms be adaptable to an RT of 0.30 seconds). More than 350 first-graders and third-graders, and adults were tested under both acoustic conditions. The results showed with the high-performance sound absorption present, speech recognition improved significantly in all test subject groups. As an example, with the high-performance absorption in place, first graders sitting in the third row recognized 22 percent more words than when the acoustic conditions were unfavorable. Similarly, adults recognized 18 percent more words under the favorable acoustic conditions.
Ceiling alternatives
While the standards often state the absorption requirements as ceiling NRC, it does not necessarily mean every space must have a standard, contiguous, modular, acoustic ceiling. That approach does not always agree with the preferred architectural style or aesthetic of the room or building. Other sound absorptive systems are permitted if they provide at least the same amount of absorption as an acoustic ceiling of NRC 0.90.
An equal amount of absorption can be achieved with a variety of acoustic metal or wood ceilings—suspended, horizontally oriented, clouds, or islands—or vertically oriented baffles. The first step is to determine how much absorption a ceiling with NRC 0.90 would have provided.
A sabin is the unit of sound absorption. Sound-absorptive elements that hang free in space, such as acoustic islands and baffles, have their performance specified in sabins rather than NRC. There are both metric and imperial sabins—it is important to distinguish between the two when reviewing product information.
Metric
For every square meter of floorspace, NRC 0.90 ceiling provides 0.9 metric sabins of absorption. Another way to look at it is to multiply the total area of the floor in square meters by 0.9 metric sabins per square meter to get the total number of metric sabins required inside the room by any absorption system.
Example
A 100-m2 (1076-sf) classroom should have 90 metric sabins of absorption over it (100 m2 x NRC 0.90 = 90 metric sabins). If a baffle provides 1 metric sabin of absorption each, then 90 baffles would be needed over the classroom.
Imperial
For every square foot of floorspace, an NRC 0.90 ceiling provides 0.9 imperial sabins of absorption. Therefore, multiply the area of the floor in square feet by 0.9 sabins per square foot to get the total number of imperial sabins required inside the room by any absorption system.
Example
A 1000-sf (93-m2) classroom should have 900 imperial sabins of absorption over it (1000 sf x NRC 0.90 = 900 imperial sabins). If a baffle provides 10 imperial sabins of absorption each, then 90 baffles would be needed.
Conclusion
Building standards, guidelines, and rating systems are now requiring high-performance acoustic absorption overhead with a minimum NRC of 0.90. This requirement is based on both quantitative research and studies showing the positive impact on occupant well-being in offices, schools, and healthcare facilities. Specifiers should remember complying with the high NRC requirement may impact other acoustical requirements, such as minimum airborne sound isolation between vertically oriented rooms. Other sound-absorptive systems, such as acoustic islands and baffles, can be used in lieu of ceilings if they provide equivalent absorption.
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). He authors technical articles and speaks publicly on the topic of optimizing acoustic experiences. Madaras can be reached at gary.madaras@rockfon.com.
