Acoustic characteristics of urban streets in relation to scattering caused by building facades

doi:10.1016/j.apacoust.2006.01.010

Applied Acoustics

Volume 68, Issue 3, March 2007, Pages 310-325

https://doi.org/10.1016/j.apacoust.2006.01.010 Get rights and content

Abstract

The relationship between scattering and the acoustic characteristics of urban streets is examined by computer simulation. The simulation method is a combination of the image method for specular reflection and the radiosity method for scattering reflection. The findings are as follows: (1) the effect of scattering on the SPL appears as an increase at short distances and as a decrease at great distances. The range of the increase in SPL is larger in high-facade streets. In low-facade streets, the primary effect of scattering on SPL is a decrease in SPL. (2) In low-facade streets the reverberation time is determined by the sum of absorption coefficient and scattering coefficient. In contrast, in high-facade streets, the reverberation time is determined by the absorption coefficient. (3) The simulated result for the reverberation time shows good agreement with measured value in actual streets. (4) The estimated values for the sum of absorption coefficient and scattering coefficient of facades of actual urban streets range from 0.1 to 0.25.

Introduction

A number of studies have examined the sound propagation characteristics of streets. By the 1970s, scattering caused by building facades was known to be an important factor in sound propagation in streets. Lyon [1] cited Delany et al.’s [2] measurement of sound pressure level in an actual street, which indicated a decay of −8 dB/dd at a distance of 20–100 m from the source, as good evidence for scattering reasonably close to the source. Davies [3] calculated the sound pressure level based on a model that considers both geometrical reflection and diffused energy. His results revealed a considerable increase in sound level close to the source due to scattering. Steenackers et al. [4] measured the sound decay curve in actual streets and found that wider streets have a larger apparent absorption coefficient, which includes diffusion. Scattering is included in the apparent absorption coefficient of his model, which therefore cannot show the sound level increase due to scattering. Kang [5] compared the calculation results for two boundaries: diffusely and geometrically reflecting surfaces. Although his study provided useful insight, his calculations were not useful for explaining the actual conditions of a street, in which reflection from building facades is neither completely diffuse nor completely specular.

None of these previous studies systematically examine scattering of various degrees and so cannot provide a useful perspective on the effect of scattering on sound propagation in actual streets. The purpose of this study is to demonstrate the relationship between scattering and the acoustic characteristics of urban streets. The acoustic indices examined in the present study are sound pressure level (SPL) and reverberation time.

Section snippets

Calculation method

The simplest model of a street consists of three surfaces: two parallel facades and the ground surface. The upper side and street ends are open and do not cause reflections. The dominant reflection that characterizes the street sound field is the repeatedly reflecting sound between the two parallel facades. In this model, the reflection consists of two components: specular reflection and scattering reflection (see Fig. 1).

The total sound energy density at the receiver in the street is given by

Sound pressure level (SPL)

Fig. 8 shows the calculated SPL, in which the abscissa represents the x-directional distance. The effect of scattering on the SPL appears as an increase at short distances and as a decrease at great distances. The range of the increase in SPL is larger in high-facade streets. However, the level change due to scattering is not large. The largest increase in SPL at a short distance, just over 1 dB, is observed for the case of high facades (h = 30 m) and an absorption coefficient a = 0. In every other

Conclusions

The acoustic characteristics of urban streets are examined using computer simulation in relation to scattering caused by building facades. The simulation method is a combination of the image method for specular reflection and the radiosity method for scattering reflection. The findings of the present study are as follows:

1.
The effect of scattering on the SPL appears as an increase at short distances and as a decrease at great distances. The range of the increase in SPL is larger in high-facade

References (7)

J. Picaut et al.
A scale model experiment for the study of sound propagation in urban areas
Appl Acoust
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R.H. Lyon
Role of multiple reflections and reverberation in urban noise propagation
J Acoust Soc Am
(1974)
M.E. Delany et al.
Propagation of traffic noise in typical urban situations
Nat Phys Lab Rep
(1971)

There are more references available in the full text version of this article.

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Acoustic characteristics of urban streets in relation to scattering caused by building facades

Abstract

Introduction

Section snippets

Calculation method

Sound pressure level (SPL)

Conclusions

Appl Acoust

Role of multiple reflections and reverberation in urban noise propagation

J Acoust Soc Am

Propagation of traffic noise in typical urban situations

Nat Phys Lab Rep