Prediction of the Effectiveness of a Sound-Masking System in an Open-Plan Office Including the Lombard Effect

Abstract

NoiseSession 4aNSa: Effects of Noise on Human Performance and Comfort I 4aNSa6. Prediction of the effectiveness of a sound-masking system in an open-plan office including the Lombard Effect Sound masking can improve speech privacy in rooms by increasing background-noise levels that mask distracting speech sounds. The Lombard Effect indicates that an increase in background-noise level can increase talker voice levels, reducing speech privacy and the benefit of a sound-masking system. To investigate this, a model of an existing open-plan office was created in CATT-Acoustics and validated. The model was used to predict speech-transmission index (STI) and the effectiveness of a sound-masking system, without and with the Lombard Effect, described by the existing Lombard Voice Model. Predictions were made for ambient-noise levels of 30, 40 and 45 dBA, at various distances from a primary talker, and for 0-4 secondary talkers. With 30-dBA ambient noise, STIs at 1 and 4 m varied with the number of talkers from 0.67-0.91 and 0.23-0.62 without the sound-masking system, from 0.58-0.70 and 0.13-0.25 with it but ignoring the Lombard Effect, and from 0.64-0.73 and 0.18-0.27 with the Lombard Effect. The Lombard Effect reduced the benefit of the sound-masking system by 14-67% and 5-50%. With higher ambient noise, the system is less effective; the Lombard Effect can cancel its benefit, resulting in increased STI (decreased privacy) with the system operating.