Influence of the tyre impedance on CPX level used to evaluate tyre/road noise

For traffic noise studies CPX measurements are used to evaluate the noise-reduction of a road surface.CPX measurements as described in ISO/DIS 11819-2 are carried out at microphone positions close to predefined tyres at constant speed. The dominant CPX sound source is the tyre’s rolling noise as a result of tyre/road interaction, which - apart from the acoustic properties of the road surface - is mainly determined by the properties of the tyre.To ensure continuous quality and comparability of CPX measurements, the variation of acoustically relevant properties of the reference tyres must be taken into account to reduce measurement uncertainties. Thus, to ensure comparability, the standard ISO/TS 11819-3 specifies Shore hardness values to be checked at regular intervals and compared with normative values. According to our experience in CPX-measurements, determining the Shore hardness of the tyres is not sufficient to describe the reference tyres’ acoustically relevant properties. So, as an additional parameter the mechanical impedance of different reference tyres was measured and compared to their Shore hardness and CPX levels on different road surfaces.Based on these results, conclusions are drawn about the usability of the tyre impedance to increase the quality and comparability of CPX measurements

Influence of the tyre impedance on CPX level used to evaluate tyre/road noise

For traffic noise studies CPX measurements are used to evaluate the noise-reduction of a road surface.CPX measurements as described in ISO/DIS 11819-2 are carried out at microphone positions close to predefined tyres at constant speed. The dominant CPX sound source is the tyre’s rolling noise as a result of tyre/road interaction, which - apart from the acoustic properties of the road surface - is mainly determined by the properties of the tyre.To ensure continuous quality and comparability of CPX measurements, the variation of acoustically relevant properties of the reference tyres must be taken into account to reduce measurement uncertainties. Thus, to ensure comparability, the standard ISO/TS 11819-3 specifies Shore hardness values to be checked at regular intervals and compared with normative values. According to our experience in CPX-measurements, determining the Shore hardness of the tyres is not sufficient to describe the reference tyres’ acoustically relevant properties. So, as an additional parameter the mechanical impedance of different reference tyres was measured and compared to their Shore hardness and CPX levels on different road surfaces.Based on these results, conclusions are drawn about the usability of the tyre impedance to increase the quality and comparability of CPX measurements

Separating the contributions from air-pumping and tyre vibrations by speed dependency analysis of tyre/road noise

Traditionally tyre/road noise has been divided into low-mid frequency noise caused by tyre vibrations and high frequency noise caused by various air flow related mechanisms, "air-pumping". It has also been assumed that these two processes grow in importance with different (vehicle) speed exponents. The purpose with this work is to investigate how to extract the different noise sources by a speed exponent analysis. Such analysis tool would e.g. indicate under which circumstances it is necessary to include air flow related sources in a tyre/road noise prediction model. The results show that it is possible to extract components of tyre/road noise that grow with the speed to the power of two and four. Expecting these contributions to be connected to tyre vibrations and air flow related source mechanisms respectively, it is found that the latter are present at surprisingly low frequencies. In addition, modelled results, only taking into account noise created by tyre vibrations, also show speed exponents larger than two. It is concluded that tyre vibrations can generate noise with a range of speed exponents making it futile to separate the two main tyre/road noise source mechanisms by a speed exponent analysis

Porous ground, crops, and buried resonators

Transport noise travelling near to naturally occurring porous ground surfaces, such as grassland, is reduced at frequencies relevant to noise control as the result of interference between direct and groundreflected sound known as the ground effect. Although it is observed frequently that different types of naturally occurring ground surfaces give rise to different ground effects, little thought has been given to deliberately choosing ground to give an improved noise reduction. In this chapter, results of calculations and measurements are provided that can inform this choice. Dense vegetation, in the form of ground cover or crops, contributes to ground effect as a result of the penetration of roots into soil and adds extra attenuation due to scattering by leaves and stems. Calculations are provided that suggest the potential usefulness for noise control of certain combinations of ground and crops. Experiments and calculations are reported showing that ground that is otherwise acoustically hard, such as nonporous asphalt or concrete, can be altered to be more effective for noise reduction by being made porous or by inserting porous strips or patches composed, for example, from gravel. Porous asphalt road surfaces are used to reduce both noise generation and propagation from road–tyre interaction. Their effectiveness for reducing traffic noise can be increased by burying preformed resonating chambers. Resonators also can be buried in hard or porous ground to reduce noise. Laboratory data and predictions are presented that demonstrate the usefulness of this method

\uc5tg\ue4rder i utomhusmilj\uf6n f\uf6r att minska buller fr\ue5n v\ue4g- och t\ue5gtrafik – resultat fr\ue5n EU-projektet HOSANNA

Denna artikel ger en kort \uf6versikt av buller\ue5tg\ue4rder, resulterande fr\ue5n EU-projektet HOSANNA, f\uf6r minskning av buller fr\ue5n v\ue4g- och sp\ue5rtrafik under ljudets utbredning. Dessa verktyg inkluderar anv\ue4ndning av ny sk\ue4rmdesign, plantering av tr\ue4d, f\uf6rb\ue4ttringar av mark- och v\ue4gytor samt vegetation p\ue5 byggnadsfasader och tak, med hj\ue4lp av naturmaterial, s\ue5som vegetation, jord och andra substrat i kombination med \ue5tervunnet material och artificiella element. De akustiska ins\ue4ttningsd\ue4mpningarna bed\uf6ms genom numeriska ber\ue4kningar, perceptuella effekter och kostnadsnyttoanalys. En betydande minskning av buller fr\ue5n v\ue4g- och sp\ue5rtrafik f\uf6ruts\ue4gs f\uf6r ett 1-m-h\uf6gt urbant bullerskydd. Detta kan f\uf6rb\ue4ttras, upp till ca 10 dB ins\ue4ttningsd\ue4mpning, genom att placera ytterligare skydd mellan k\uf6rf\ue4lten. Ett 3 m brett och 0,3 m h\uf6gt rutn\ue4t, ett omsorgsfullt planterat 15 m brett tr\ue4db\ue4lte samt att ers\ue4tta 50 meter asfalterad mark med gr\ue4smark f\uf6rutsp\ue5s ge bullerminskningar om 5–8 dB, medan anv\ue4ndning av fasadvegetation och gr\uf6na tak kan minska niv\ue5n p\ue5 innerg\ue5rdar med upp till ca 4 respektive 7 dB. Tr\ue4db\ue4lten visar sig vara mycket kostnadseffektiva och kombinationer av h\uf6ga sk\ue4rmar med en rad av tr\ue4d minskar de negativa effekterna av vind p\ue5 bullersk\ue4rmars ins\ue4ttningsd\ue4mpning. Gr\uf6na tak kan minska bullret p\ue5 den tysta sidan av byggnader

NOVEL SOLUTIONS FOR QUIETER AND GREENER CITIES

This brochure summarizes the main findings of the research project “HOlistic and Sustainable Abatement of Noise by optimized combinations of Natural and Artificial means” (HOSANNA). The project aimed to develop a toolbox for reducing road and rail traffic noise in outdoor environments by the optimal use of vegetation, soil, other natural materials and recycled materials in combination with artificial elements

NOVEL SOLUTIONS FOR QUIETER AND GREENER CITIES

This brochure summarizes the main findings of the research project “HOlistic and Sustainable Abatement of Noise by optimized combinations of Natural and Artificial means” (HOSANNA). The project aimed to develop a toolbox for reducing road and rail traffic noise in outdoor environments by the optimal use of vegetation, soil, other natural materials and recycled materials in combination with artificial elements