The effect of sound masking on employees' acoustic comfort and performance in open-plan offices in Canada

Abstract

Sound masking systems are commonly used in open-plan offices to generate a controlled minimum level of background sound, in order to decrease the signal-to-noise ratio of intrusive speech and blend out transient office noise. However, a question in the acoustical design of offices is whether the self-generated noise of occupants may alone be sufficient to provide the background sound level conditions necessary to achieve similar levels of speech privacy and acoustic comfort as sound masking systems. This study examines the relationship between occupant-perceived speech privacy and acoustic comfort under three different acoustic scenarios (no masking, controlled 42 dBA, and 47 dBA masking sound levels). The study was conducted pre-COVID-19 in two separate open-plan offices located in Quebec, Canada that at the time were close to full occupancy. Employees completed subjective questionnaires before and after each change in conditions, focusing on how the sound environment impacted their comfort and work performance during the study. Statistical results show that the occupants were significantly more satisfied during the two sound masking conditions in comparison to the no-masking condition, where only the occupant-generated and exterior/mechanical system noise was present as the background sound. Implications for open-plan offices with lower occupancy conditions post-COVID-19 are discussed.

THE USE OF ADAPTIVE SOUND MASKING SYSTEMS IN OPEN-PLAN OFFICES: HOW THEY WORK AND THE RELATIVE IMPROVEMENTS FOR SPEECH PRIVACY & ACOUSTIC COMFORT

“…Considering an ΔLAeq-Lmk = 0 dB would mean that the masking sound is the dominant sound in the office environment, and that an ΔLAeq-Lmk = 10 dB means the masking sound has almost no contribution to the overall ambient noise, then a value of 5 dB for ΔLAeq-Lmk appears to be a reasonable value to evaluate at what point any discomfort due to an increasing contribution of the higher level of masking sound may occur. Whilst ISO 3382-3 4 introduces the comfort distance metric as the level at which intruding speech falls below 45 dBA, 42 dBA is taken in this study as a lower limit for occupant discomfort based on NRCC guidance that levels lower than this significantly reduce the effectiveness of sound masking for speech privacy (this is supported by the findings of Haapakangas et al 13 and Lee et al 12 wherein lower residual background sound levels were found to be associated with a higher degree of noise disturbance. A masking sound level lower than 42 dBA (Lmk<42 dBA) should therefore be considered as comfortable even if the LAeq is not 5 dB above Lmk.…”

“…Indeed, background levels below this would make achievement of the ISO 3382-3 recommended distraction distance (<5m) very difficult to otherwise achieve in most open-plan offices. A recent subjective study by Lee et al 12 across large open-plan offices determined that a masking level of 42 dBA was found to be more pleasant and less distracting than at 47 dBA, whilst both masking sound conditions scored more highly than when the masking system was muted (residual level approximately 38 dBA). Nevertheless, this minimum masking level can be set to meet the needs of the acoustical consultant's specifications.…”

Sound masking by a low-pitch speech-shaped noise improves a social robot’s talk in noisy environments

“…Sound masking is a process of adding a steady state nonfluctuating background sound to an environment to mask or cover up unwanted noises (Chanaud, 2007). The core idea behind using masking sounds is to make the tempo-spectral properties of the background speech less easily detectable and hence, reduce the distraction caused by them (Mackenzie et al, 2021). A stationary noise with a slope of −5 dB per octave is the most commonly used type of masking sound (Hodgson and Warnock, 1992).…”

Using active noise-cancelling headphones in open-plan offices: No influence on cognitive performance but improvement of perceived privacy and acoustic environment

“…Sound masking methods raise the background noise through loudspeakers in the room (usually a −5 dB/octave filtered pink noise) and therefore cover speech signals. They have already been researched in detail and are able to increase cognitive performance in the office (Bradley 2003;Haapakangas, Kankkunen, et al, 2011;Liebl, Assfalg, and Schlittmeier 2016;Hongisto et al, 2016;Zaglauer, Drotleff, and Liebl 2017;J. Lee et al, 2021).…”