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Acoustic satisfaction will exist if occupants' needs for noise level and privacy are met.
Office acoustics must be appropriate for the job: the more supportive the environment, the easier it is to work. Because sound travels easily in an open-plan office, employees can experience two significant problems: many distractions and little speech privacy.
Distraction
Distractions compromise employees' physical and task needs, making it difficult for them to work. Researchers Tom Demarco and Timothy Lister found that it takes approximately fifteen minutes for employees to regain a state of deep concentration ("flow") after an interruption [1]. After nine distractions, half the workday can be lost.
An employee becomes distracted when an unwanted, unexpected noise intrudes into his or her cubicle.
In general, noise levels above 45-50 dB(A) tend to be disturbing [2]. Distraction also tends to increase with the presence of too much high-frequency sound relative to low-frequency sound. High-frequency sound should not be eliminated from the environment because it masks speech well, but a balance between low and high is required for satisfaction.
Sources: Distracting noises can be machine or human in source; they can be intermittent (speech, phone, printer) or continuous (ventilation system). Intermittent noises are disturbing because they break relative quiet. Continuous noises can be annoying when they are too loud or have a distracting character: rumble, roar, or hiss.
Receivers: In an open-plan office, any occupant is a potential receiver.
Speech Privacy
Speech privacy affects employees' privacy needs and organizational effectiveness. Speech privacy exists if a neighbour cannot understand a person's conversation. Inadequate speech privacy creates dissatisfaction because employees dislike feeling that their conversations are public. Client, personnel, and product confidentiality can also be difficult to maintain if cubicle occupants can hear information not intended for them.
Speech privacy depends on the loudness of the source (voice), the propagation paths, and the loudness of any background noise. Two acceptable levels of privacy have been identified for offices: confidential and normal. [3]
Confidential Privacy: Confidential privacy exists if a listener can understand only a few words but no entire sentences or phrases. It is important for executive and sensitive spaces. Confidential Privacy has been given a Speech Intelligibility Index (SII) rating of 0.1 (Articulation Index [AI] 0.05)
Normal privacy: Normal privacy exists if the speech is intelligible to an active listener only; an uninterested listener would be able to tune-out the conversation. The normal privacy SII rating is 0.2 (AI 0.15).
References:
1: Demarco, T. & Lister, T. (1987). Peopleware: Productive Projects and Teams. New York: Dorset House Publishing Co.
2: Veitch, J.A., Bradley, J.S., Legault, L.M., Norcross, S. & Svec, J.M. (2002). Masking Speech in Open-Plan Offices with Simulated Ventilation Noise: Noise Level and Spectral Composition Effects on Acoustic Satisfaction. COPE project report. Ottawa, Canada: Institute for Research in Construction/National Research Council (IRC/NRC).
3: Bradley, J.S. (2003). "The Acoustical design of conventional open plan offices." NRCC-46274. Ottawa, Canada: Institute for Research in Construction/National Research Council (IRC/NRC) and American Society for Testing and Materials (ASTM). (1976). Acoustical Environment in the Open-Plan Office (Task Group E33.04C). Philadelphia, PA: ASTM.
