The Influence Of Street Space Shape And Interface On Sound Environment

Street is the framework of a city and also an important urban public place.It can not only reflect the urban landscape and characteristics but also interpret the urban culture.However,in the implementation of modern urban planning,the urban street space is seen more as a traffic attributes,its public space attributes are dimmed,and its acoustic environment has not been attracted enough attention.As the automobile era is approaching,the urban streets have become more and more crowded with more traffic problems and lots of environmental problems have arisen.In order to solve the problem of urban traffic congestion,planning measures such as th e “block system” and one-way traffic are used to solve traffic problems,but they also cause more vehicles to enter urban branch roads and residential roads at higher speeds.The acoustic environment deteriorated further.Based on surveying the current status of acoustic environment of the urban streets in China,this paper has analyzed the current acoustic environment and noise pollution in the urban streets,based on which and according to field measurements,computer simulation s and statistical analyses of the results,the influence of street space shape and street interface on street sound environment are studed.As to the actual survey of acoustic environment,this paper has chosen the urban streets in Harbin as the research object.Based on the functio nal classification of the street,the sample has been collected in 72 streets so as to measure the noise level comprehensively.According to the survey result,the problem of noise pollution at the daytime has been present on the arterial road,branch and street in the residential area at different levels.The noise pollution on the branch street at the daytime has been most serious only with a pass rate of 51.9 %.There is no significant difference in the environmental noise between different city areas(new city area and old city area).There is a significant difference in the environmental noise between different types of street(trunk road,branch and residential road).As shown by universal indexes for noise source,traffic noise and social life noise are the two most important noise sources on the living streets.According to the comparison of the difference between different sections on the same street,the street space form and street interface have a significant influence on the acoustic environment of the street.The influence can be found on different types of street(trunk road,branch and residential road).As to the influence of street space form on the acoustic environment of the street,this research is based on the actual condition of the 144 sections of the living streets.Reliable parameters about space shape have been extracted.The research models for point sound source and line sound source have been also built respectively.The computer simulation has been conducted to gain the characteristics of sound propagation.The statistical principles have been utilized to gain the laws regarding sound propagation on the street space based on the actual condition.The model for predicting the acoustic environment for the urban living street space has been also built.As shown by the research,the spatial parameters of different streets have different influence on different acoustic indicators.As to the model for predicting the sound propagation of point sound source,acoustic damping amount is linearly and positively related to the logarithm of sound propagation distance.For the same distance of sound propagation,acoustic damping amount is smaller with a larger sectional enclosure and planar enclosure as well as a smaller driveway width.Reverberation time(RT30)does not change much in the propagation direction.RT30 will increase with the sectional enclosure,planar enclosure,width and average elevation height.The distribution of the early acoustic damping time(EDT)has displayed a certain typical feature in the propagation direction.EDT value will rise dramatically when the sound propagation distance reaches 20 to 30 meters for most streets.Before or after this point,EDT value remains stable.EDT rises more dramatically with a wider driveway and larger front sectional enclosure.As to the line sound source prediction model,the noise level on the tested point is higher than that of the empty field due to the effect of the street space.The increment is named as sound level increment of space form(?Lspace).The research shows that the noise level on the street are mainly ranged from 0.5 to 3.0 d B.?Lspace will be larger with a narrower driveway,larger average height of building interface,larger sectional enclosure and larger planar enclosure.RT30 ranges from 1.5 to 2.5 seconds.EDT ranges from 1.5 to 2.0 seconds.EDT will be larger with a wider street,higher building interface,larger planar enclosure and even distribution of planar opening.With regard to the influence of acoustic reflection of street interface on the acoustic environment,the researcher has combined the sound source positioning technology and sound ray theory to analyze the acoustic reflection characteristics for six categories of street interfaces.The factors influencing the acoustic reflection characteristics of the building interface have been also discussed.It is found that the type of acoustic reflection has a decisive influence on the acoustic reflection characteristics of the building elevation.The reflected sound signal generated by the diffraction is weakest and does not have a significant response frequency.The reflected sound signal generated by mirror reflection is strongest and also has a significant response frequency.Response frequency is influenced by the acoustic characteristics of the building materials in the reflection area.The reflected sound of angular reflector is relatively strong and also has a significant response frequency.The strength and frequency of the reflected sound signal is influenced by the size of the angular reflector.The response frequency of the diffused reflected sound with an irregular shape and the strength of reflected sound signal are related to the reflection angle and reflected sound distance.If the reflection angle is larger,the response frequency is larger and sound pressure is also lower.The green belt in the front will not only reduce the strength of the reflected sound of the building elevation but also cause the time delay effect on the reflected sound signal.Based on the conclusions above,this paper has discussed real cases and simulation cases.From the perspective of designer,this paper has also summarized three design strategies and specific methods for improving the acoustic environment on the street.According to the features of noise source of the street,this paper has proposed two design strategies,namely limiting the noise source and creating the street sound view.Considering the influence of the parameters of street space form on the acoustic environment,this paper has also put forward two design strategies for acoustic environment,namely improving the openness of the street planar space and improving the openness of street sectional space.According to the sound reflection characteristics of street interface,this paper has put forward three design strategies,namely weakening the reflected sound of angular reflector,changing the sound reflection direction of building interface as well as increasing the sound absorption coefficient of building interface.