ASHRAE RP 1852 toward a unified metric for speech privacy in high-performance buildings: Determination of a suitable metric for both open-plan and closed offices through measurement

Various metrics have been developed since the 1960s to measure speech privacy (SP) within office spaces, but have diverged between those intended for open-plan (e.g., Articulation Index, ASTM E1130 or Speech Transmission Index, ISO 3382-3) or those for closed offices/rooms (e.g., Speech Privacy Potential, or Speech Privacy Class, SPC, ASTM E2638). Others (e.g., Speech intelligibility Index, ANSI S3.5) do not have a standardized use in offices. No single metric has been validated for both office types. Furthermore, SII, AI, and STI struggle to differentiate between unintelligibility and inaudibility, while SPC’s relationship to distraction and use in open plan is underexplored. This ASHRAE-funded research project (RP 1852) aimed to determine and validate a single metric and method for both space types to accurately rate or predict SP (in terms of audibility, intelligibility, and distraction). 308 open-plan workstations and 44 closed rooms (private offices and meeting rooms) across 5 sites were assessed using the aforementioned metrics and associated methods and variants thereof. Statistical analysis of 1312 open-plan and 1532 closed room measurements reveals the relations between SP metrics. Effects of source/receiver locations and room boundaries are described. The strengths and weaknesses are discussed, with ultimately the SPC being the strongest candidate for a unifying metric across spaces.