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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.

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An electronic sound-masking system reduces workers' distractions in open-plan spaces by utilizing an artificial broadband sound. The artificial sound should raise a background noise level spectrum to the targeted masking sound level uniformly over the entire area.Uneven distribution of the masking sound levels can cause unnecessary loud background noise or inefficient sound masking performance at the same time and in different locations. The ASTM E 1573-18 standard provides a procedure to quantify the uniformity of the masking sound but does not specify any acceptable degree of uniformity. Thus, this study aims to investigate the uniformity of the masking sound field in an open-plan space under varying room acoustic conditions. The acoustic measurement was carried out in an open-plan office with a measurement grid of 0.6 m. The spatial variation of the sound pressure levels was calculated with the measured one-third-octave band SPLs from 250 Hz to 4 kHz. The study also employed computer-aided acoustic simulation to find key design parameters, impacting the uniformity of the masking sound. The results show that the number of loudspeakers, a partition height, scattering, and absorption coefficients can significantly influence the spatial uniformity and speech privacy within the space. Finally, the results proposed an acceptable variation of the masking sound field by examining the Articulation Index (AI) change in the space.

Electronic sound masking systems raise the ambient sound level in offices to a controlled minimum sound level in order to increase speech privacy and reduce distractions. Sound masking systems are calibrated to provide the most uniform sound field achievable, as a spatially non-uniform masking sound field could result in occupant perception and uneven speech privacy conditions. Tolerances for acceptable spatial uniformity vary between specifiers, and may be based on different evaluation methods using only a few discrete measurement points to represent an entire office space. However, the actual uniformity of a masking sound field across an office, and the parameters influencing it, has not been widely investigated. Thus, this study aims to investigate the masking sound uniformity in a typical open-plan office space using fine-grid measurements conforming to measurement method of ASTM E1573-18. Percentages of measured locations where the sound pressure levels were within specified tolerances (with increments of 0.5 dB) were calculated using the measured 1/3 octave band levels. The research also utilized geometric acoustical simulations to investigate how physical office parameters (number of loudspeakers, partition heights, ceiling absorption, and diffusion characteristics) affect the sound field uniformity of the sound masking system.