Prediction study of factors affecting speech privacy between rooms and the effect of ventilation openings

Abstract

Ventilation openings in partitions separating rooms reduce sound isolation and cause dissatis-faction with speech privacy. To better understand how ventilation openings affect the speech privacy relative to other factors and whether acoustical treatment would be effective, a simple prediction model based on diffuse-field theory was applied. This model considers two adjacent rooms with a separating wall, possibly containing a ventilation opening. The source room contains a talker; speech privacy, determined from the absence of speech intelligibility as quantified by the Speech Intelligibility Index (SII), is predicted for a listener in the receiver room. The effects of talker vocal effort, room size and surface absorption, background-noise level, partition transmission loss and ventilation-opening size were predicted. SII was greatly affected by all of these factors, showing that to design for speech privacy it is insufficient to consider the partition performance alone. Speech privacy cannot be obtained if a wall contains an untreated opening with an area 0.1% of the wall area. To achieve speech privacy, ventilation openings must be treated acoustically. The SII is significantly increased (speech privacy reduced) if the opening’s effective open area exceeds 10% of that of the wall, and doubles if the opening’s effective open area exceeds 50%.