FACILITIES MANAGEMENT WHITE PAPERS Achieving Effective Office Acoustics Understanding acoustics leads to the inclusion of sound masking in office designs Niklas Moeller, LogiSon Acoustic Network Studies show that acoustics are an essential consideration in meeting what is arguably the primary goal of the office: to provide a setting conducive to optimal work performance. In fact, a survey of 400 business managers conducted by the Building Owners and Managers Association (BOMA) and the University of Maryland identifies noise control as the greatest opportunity for productivity improvement with an estimated average increase of 26 percent. Such statistics suggest that the benefits of an effective acoustic environment on workplace satisfaction and profitability would be substantial. But how can one create an effective acoustic environment? Discussions of noise control methods in offices typically revolve around the ABC Rule, meaning Absorb, Block and Cover Up, but the tendency is to rely upon only the first two of these three methods. While these two steps are necessary, it is the exclusion of the third method, the masking of sound, which prevents many facilities from achieving the desired acoustical conditions. Though sound masking systems have been used for over twenty-five years and in thousands of facilities worldwide, they remain novel to many people; therefore, it is useful to provide a brief description of this technology. Basically, a sound masking system consists of a series of speakers that distribute an electronically generated background sound within a facility. Because the human ear cannot perceive simultaneous sounds of similar volume and frequency, unwanted noises are more difficult, or impossible, to hear or comprehend. Many people refer to such systems as white noise systems; however, this is a misnomer. The term "white noise" describes a specific type of sound used in early masking systems developed in the 1970s. Newer sound masking products do not distribute a white noise signal; rather, they offer an engineered sound that is much more comfortable, unobtrusive and effective. Sound masking greatly contributes to four key acoustical requirements. This fact becomes clear when we consider those requirements and analyze one company's attempts to fulfill them. A well-known U.S. company recently completed their new headquarters in Europe and was unhappy with the results with respect to noise. The office was finished with reflective surfaces on ceilings, walls and floors and no sound masking system had been installed. After the company moved in, they discovered that noise levels in their office were quite high due to the reflection of sounds from the hard surfaces back into the space. Sounds traveled a great distance as they reverberated off the ceilings, floors and walls. The space was very difficult to work in. It was hard to concentrate. There was a modest amount of privacy, but only due to the high levels and quantity of noise. How could they resolve these issues? The first requirement is to create a background sound level that is high enough to mask noises and yet low enough to be comfortable. The noise floor (the level of continuous sound that characterizes a space at any given time) should be too high or too low because overly loud environments are irritating and tiring, while overly silent environments provide little noise control or speech privacy. Since offices exist for active purposes, silent environments are not an option. Yet the typical response to acoustic issues such as those in our case study is to try to achieve silence by using the first two of the three methods of noise control: blocking noises and adding absorptive materials to the space. In our example, the company was advised that they could lower the noise levels in their office by completely renovating the area with absorptive materials. This action was a positive first step, but it was not sufficient to provide an acceptable acoustic environment. Absorptive ceiling tiles and furniture partitions reduce the average sound levels in a space by decreasing the volume of noises reflected back into the office. However, they also reduce the noise floor and can actually produce a space that is too quiet. While they made the space somewhat more comfortable, these materials also eliminated the modest degree of speech privacy that had existed in the space. Conversations became more intelligible over a greater distance. Absorptive materials reduce the noise floor making conversations intelligible over a greater distance Occupants' level of speech privacy and their ability to concentrate is influenced by the signal-to-noise ratio, or the volume of conversation or sound relative to the background level or noise floor. The greater the sound relative to the background, the more noticeable and understandable it is. While sounds decay in volume over distance, low background levels mean that they can be clearly heard from afar. A masking system dramatically reduces this distance by raising the background sound level. Any voices or sounds that have decayed to a level below the masking will be covered up and go unheard. Over shorter distances, masking may not prevent one from hearing that someone is speaking, but it will inhibit one's ability to understand what is being said. This effect is a key benefit because comprehensible speech is the most distracting and least private. Sound masking increases speech privacy Referring again to our case study, the company's sole reliance upon absorptive materials also failed to meet the third acoustical requirement, which is low dynamic range. This term is defined as the variation in the volume of sound over time or the difference between the peak sound levels and the noise floor in the space. Our senses easily detect such changes and it is difficult to ignore them; therefore, the higher the dynamic range, the harder it is to "block out" noise. The absorptive materials used in the European headquarters had no effect on the high dynamic range within the space. Masking would dramatically reduce the variation in sound levels by raising the noise floor in a controlled manner. The lowest level of sound to occur in the space would become that generated by the masking system and all sounds beneath the masking level would become unintelligible or imperceptible. With peak levels minimized through blocking noise, as well as absorption, the result would be a more comfortable and consistent acoustic environment. Sound masking and absorptive materials work together to lower dynamic range The fourth requirement for effective office acoustics addresses the variations in the acoustic environment found within all facilities. The type of ceiling, open air return grills, HVAC ducts or equipment, proximity to walls, and office machinery all affect the acoustic characteristics of a space. Variations in lighting, temperature and humidity are controlled and kept within certain comfort parameters, and, similarly, the fourth requirement for effective office acoustics is to minimize variations in both sound volume and frequency. Such consistency allows individuals to move within the office and work in multiple locations with minimal impact. A sound masking system is unique among methods of noise control in its ability to minimize acoustic variations because it introduces a specific background sound at controlled levels across the space. Armed with a better understanding of the determinants of an effective acoustic environment, we see that office designs must continue to benefit from traditional noise control methods, such as blocking and absorbing noise, and that sound masking must also be integrated into the total acoustic solution. For more information, please take the Guided Tour (in Macromedia Flash) on our website. Click on the "Effective Office Acoustics" and "Sound Masking" links under the "Guided Tour" header. About the Author Niklas Moeller is Vice President of K.R. Moeller Associates Ltd., manufacturer of the Scamp® Sound Masking System and LogiSon™ Acoustic Network. Niklas has been interviewed on the subject of acoustics and/or sound masking by many magazines, including Archi-Tech, Building Operating Management and Sound & Communications. He also contributed to the development of the Canadian Standards Association's Guidelines on Office Ergonomics and the U.S. Department of Energy's Greening Federal Facilities: An Energy, Environmental, and Economic Resource Guide for Federal Facility Managers and Designers. He has published articles in Buildings, the Canadian Pharmaceutical Journal, IFMA Chapter Newsletters, Banker & Tradesman, and Canadian Property Management. He was interviewed for the television program American Architectural Review—hosted by Morley Safer—which produced a special feature on Scamp Sound Masking Systems prior to the release of the LogiSon Acoustic Network. www.logison.com