The propagation of sound in narrow street canyons

Abstract

This paper addresses an important problem of predicting sound propagation in narrow street canyons with width less than 10 m, which are commonly found in a built-up urban district. Major noise sources are, for example, air conditioners installed on building facades and powered mechanical equipment for repair and construction work. Interference effects due to multiple reflections from building facades and ground surfaces are important contributions in these complex environments. Although the studies of sound transmission in urban areas can be traced back to as early as the 1960s, the resulting mathematical and numerical models are still unable to predict sound fields accurately in city streets. This is understandable because sound propagation in city streets involves many intriguing phenomena such as reflections and scattering at the building facades, diffusion effects due to recessions and protrusions of building surfaces, geometric spreading, and atmospheric absorption. This paper describes the development of a numerical model for the prediction of sound fields in city streets. To simplify the problem, a typical city street is represented by two parallel reflecting walls and a flat impedance ground. The numerical model is based on a simple ray theory that takes account of multiple reflections from the building facades. The sound fields due to the point source and its images are summed coherently such that mutual interference effects between contributing rays can be included in the analysis. Indoor experiments are conducted in an anechoic chamber. Experimental data are compared with theoretical predictions to establish the validity and usefulness of this simple model. Outdoor experimental measurements have also been conducted to further validate the model.

High frequency sound propagation in a network of interconnecting streets

“…In practice, some energy incident on the walls is absorbed, and the simplest way of including this in the ray model (cf. [1,4]) is to introduce an absorption coefficient a 2 ½0,1, such that the magnitude I of the intensity along a ray undergoing a reflection at the boundary is attenuated according to the rule…”

Prediction of reverberation time and speech transmission index in long enclosures

“…Recently, Li and Iu presented a ''coherent'' model, or the complex image source model, for the prediction of sound propagation in street canyons, 9 long enclosures 10 and tunnels. 11 The model was based on an analytic Green's function, which allowed a variation of the reflection factors with the angle of incidence.…”

A Scale Model Study of Parallel Urban Canyons

“…Recently, Picaut et al presented the results of a successful measurement campaign in a single street canyon [16]. Also, scale model measurements have been conducted to show the usefulness of the developed models [10,16,17,18,19]. In contrast to street canyon situations, studies on squares are more rare.…”

“…Based on the assumption of diffuse reflections, the diffusion equation [8] and a radiosity based model were presented [9]. For narrow street canyons, Iu and Li showed that a coherent image sources model is necessary rather than an energy based model [10]. Other valuable contributions to modelling sound propagation in a street canyon can be found in references [11,12,13,14].…”