Metro noise-induced activity disturbances and their water sound-based countermeasures

With the rapid renewal and development of metro lines, the activity disturbances caused by metro noise inside buildings have attracted much attention. A large number of studies have explored the activity disturbances induced by aboveground railway or road traffic noises, there is a lack of research assessing the activity disturbances due to metro noise. Accordingly, this study investigated the disturbances induced by metro noise in indoor condition at four noise levels (50, 55, 60 and 65 dBA) in three kinds of stimulation conditions (calculation, judgement and memory) and the regulating effects of adding four types of water sounds (fountain, stream, water-drop and waterfall sounds) on the disturbance levels due to metro noise. Seventy-nine subjects participated in the experiment and were exposed to a series of acoustic samples before being asked to evaluate the disturbance levels using a 5-point verbal scale. The results show that under the same metro noise environments, the disturbance levels of memory were much higher than those of calculation and judgement, and compared to the disturbance level of calculation, the disturbance levels of judgement and memory were more sensitive to the change of metro noise level. Besides, when A-weighted equivalent sound pressure level lay between 55 and 65 dBA, the disturbance level of memory seemed to reduce after adding the fountain sound or water-drop sound, among which the capability of water-drop sound seemed stronger, and the mitigating effect of water-drop sound seemed to become more significant with the increase of metro noise level.