The failure of traditional traffic noise control for quiet areas

摘要

One can consider the acoustic soundscape as consisting of two parts the direct acoustic soundscape and the diffuse acoustic soundscape. This fact has important consequences whenrnattempting to change the acoustic soundscapes. The traditional approach to control traffic noise byrnmeans of noise barriers or change of traffic distribution is only valid for the areas directly exposedrnfrom sources (direct acoustic soundscape). These areas will experience a certain decrease of soundrnpressure levels when applying these noise control measures. However there will be a lower limit forrnreduction due to the presence of a diffuse acoustic soundscape. To control/modify such a diffusernacoustic soundscape has been shown very difficult by traditional means of noise control. Mainrncharacteristic of diffuse acoustic soundscapes is the presence of a multitude of sources, distributedrnover a wide area contributing evenly to the acoustic soundscape in a certain areas. Screening will onlyrnlead to a redistribution of sound, however consequences of such a redistribution will not be recognisedrnin a diffuse sound field. Absorption has been identified as a main parameter to control diffuse acousticrnsoundscapes. Reducing sound pressure levels in shielded areas such as inner-yards can only be achieved by adding acoustically absorbing areas along the transfer path between source and receiver, but especially inside the inner-yard. Redistribution of traffic flow has been shown to have a tremendous effect on the directly exposed side, but only a small effect in shielded areas.