Effect of Height-To-Width Ratio on the Sound Propagation in Urban Streets

Street geometry is one of main issues on urban design which influence sound environment as well as urban climate in a street canyon. A parametric study was performed in order to investigate the influence of height-to-width ratio (H/W) on sound fields in urban streets in terms of sound pressure level (SPL), reverberation time (T30), and early decay time (EDT). A computer simulation technique based on a hybrid method combining ray tracing and image source modeling was adopted, and an omnidirectional sound source was used. Four typical idealized urban streets were modeled, with street widths of 6 m, 13 m, 20 m, and 27 m, respectively. The H/W ratio was then changed in seven steps with varying building heights while the widths of streets were fixed. Comparisons with experimental studies showed that the computer simulation models produce reliable results for SPL and T30. It was found that the variation of SPL was affected by the H/W ratio only for narrow urban streets, and the T30 and EDT increased with an increase in the H/W ratio for both narrow and wide streets. It was also observed that the T30 decreased with increasing scattering coefficients, and the EDT significantly increased as scattering coefficients increased for H/W of 3 and 6. A line source representing road traffic noise was found to produce different tendencies in SPL and EDT, showing that SPL and EDT were relatively constant along the length.