Hong and teammates studied adding nature sounds to outdoor spaces. Study participants wore a mixed-reality head-mounted display and saw a hologram of either a sparrow or a fountain or a loudspeaker while hearing birdsong or a stream. The researchers determined via data collected outdoors, near an expressway, that “both natural sounds significantly reduced the PLN [perceived loudness of the traffic noise] and enhanced the OSQ [overall sound quality]. . . . Analysis on the preferred signal-to-noise ratio (SNR), i.e. ratio of natural sound to traffic levels, indicated a strong negative correlation between the preferred SNRs and ambient traffic noise levels. Overall, the preferred SNR of the birdsong was significantly higher than that of the water sound. . . . It was also found that there was no statistically significant difference in the reduction effect of PLN between the birdsong and water sounds.” Quantifying some of the effects seen: “When the traffic noise levels were below 70 dB, higher natural sound levels than the background noise level were considered as desirable . . . at higher traffic noise levels over 70 dB, the participants tended to prefer lower natural sound levels than the ambient traffic noise levels.” Responses to the sounds were not significantly different if people were looking at the corresponding hologram (a bird for birdsong and a fountain while hearing the water sound) or a loud speaker, which makes adding sounds to outdoor spaces via loudspeakers a much more viable option.
Joo Hong, Bhan Lam, Zhen-Ting Ong, Kenneth Oo, Woon-Seng Gan, Jian Kang, Samuel Yeong, Irene Lee, and Sze-Tiong Tan. 2021. “A Mixed-Reality Approach to Soundscape Assessment of Outdoor Urban Environments Augmented with Natural Sounds.” Building and Environment, vol. 194, 107688, https://doi.org/10.1016/j.buildenv.2021.107688