Effects of Five Speech Masking Sounds on Performance and Acoustic Satisfaction. Implications for Open-Plan Offices

The aim of this study was to compare different sounds which can be used in open-plan offices to mask distracting speech. Fifty-four subjects were tested in seven sound conditions: speech, silence and five masked speech conditions. The five masking sounds were filtered pink noise, ventilation noise, instrumental music, vocal music and the sound of spring water. They were superimposed on speech. The masked speech conditions corresponded to an acoustically excellent open-plan office in respect to the Speech Transmission Index (STI 0.38). The speech condition (STI 0.62) corresponded to the STI obtained between nearby workstations in an acoustically poor open-plan office. Silent condition (STI 0.00) corresponded to the STI measured between two nearby private office rooms. In each of the seven sound conditions, the subjects performed a short-term memory task, a proofreading task and a creative thinking task and completed a questionnaire on acoustic comfort. Compared to silence condition, shortterm memory performance deteriorated in speech condition and in most masked speech conditions. Compared to speech condition, performance improved when speech was masked with spring water sound. Ratings of acoustic satisfaction and subjective workload showed that masked speech conditions subjectively improved the working conditions compared to speech condition. Overall, the performance results and subjective perceptions showed that the spring water sound was the most optimal speech masker whereas vocal music produced negative effects similar to those of speech. The use of constant masking sounds should be preferred in open-plan offices instead of instrumental or vocal music.