In surveys of office environments that measure occupants’ satisfaction with their workspace, the intrusion of unwanted sound—noise—vies with temperature as the leading source of dissatisfaction (Harris, 1978, 1991, Sundstrom, 1994, Brill, 2001). Recent research by the Center for the Built Environment supports this finding, with more than 40% of employees responding to CBE’s occupant satisfaction survey reporting that workplace acoustics make it harder for them to do their job (CBE, 2001). Moreover, an elevated level of workplace noise has been shown to increase stress, decrease motivation and is associated with risk factors for musculoskeletal disorder (Evans, 2000).
To improve this situation, architects, interior designers, and facilities management professionals need to be able to translate a proposed design into a specific prediction of acoustical satisfaction with the resulting workspace. Over the past 40 years, acoustical consultants have in fact developed such a method. In the late 1950’s, engineers at Bolt, Beranek & Newman recognized that a majority of acoustical complaints in offices were related to speech privacy—overhearing unwanted conversations or feeling that one is overheard. Building on research at Bell Labs that correlated a listener’s ability to understand words with the ratio between the loudness of a person’s voice and the loudness of the background noise, these engineers demonstrated that a listener’s inability to understand words in a workplace setting is part of this same continuum of signal to noise. They then showed that that a series of objective measurements can establish this ratio and accurately predict an occupant’s satisfaction with their speech privacy (Cavanaugh 1962). Over the past forty years, this method for predicting speech privacy satisfaction with has been simplified (Young, 1965), adapted for use in open plan environments (Pirn, 1971) and consolidated into worksheet formats for both open and closed office environments (Egan, 1972). Versions of this calculation procedure have been published in leading texts on acoustical design, including ones by Cavanaugh (1999), Egan (1988), and Salter (1998).