An experimental study on the acoustic characteristics of outdoor spaces surrounded by multi-residential buildings

A comfortable sound environment in the outdoor spaces of apartment complexes contributes to the improvement of the overall environmental quality. It is expected that the characteristics of room acoustical parameters and sound pressure level (SPL) attenuation of outdoor spaces surrounded by multi-residential buildings depends on many design factors such as the openness, volume, and building layouts, etc. The aim of this study is to clarify the influential factors determining room acoustical parameters and SPL attenuation in outdoor spaces that are surrounded by buildings with complicated topographical conditions. A series of measurements was carried out for 15 outdoor spaces in 6 apartment complexes with different building layouts. The 15 outdoor spaces were categorized into 4 types of building layouts: linear-shaped, parallel-shaped, U-shaped, and square-shaped. The result showed that reverberation time (RT) at 500 Hz and 1000 Hz is relatively long, over 4 s, with uneven RT distribution showing a non-diffuse field. With increasing source to receiver distance, the RT and early decay time (EDT) increased logarithmically. On the other hand, the Definition (D50) and rapid speech transmission index (RASTI) decreased with increasing source to receiver distances. The result for the SPL attenuation measured at a 20 m source to receiver distance in 10 outdoor spaces showed a 17.7 dB difference between the 10 spaces due to the influence of building geometry. An empirical method considering the openness, size-related parameters, and room constant is also suggested to predict the approximate RT and SPL attenuation in the outdoor spaces.