Source modelling of road vehicles

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Hans Jonasson
Gijsjan van Blokland
Jurek Ejsmont
Greg Watts
Marcello Luminari

The state-of-the-art of acoustic source modelling of road vehicles has been reviewed. Extensive measurements and simulations have been carried out. The aim has been to identify and quantify all relevant parameters influencing the noise emission of road vehicles. The collected information has been used to construct a source model suitable to combine with point-to-point sound propagation theory to calculate day-evening-night weighted yearly average sound pressure levels of road traffic noise. Each vehicle category is represented by two point sources, each having a specified sound power having contributions from tyre/road (rolling) noise and propulsion noise. As a minimum 3 vehicle categories are used: Passenger cars, medium heavy and heavy vehicles. Additional categories are defined. The medium heavy vehicle has two axles and the heavy vehicle has 3 or more axles but corrections are made for the number of axles. All default data refer to a reference condition: constant speed, 20 °C and the average of DAC 0/11 and SMA 0/11 road surfaces. Deviations from these conditions are corrected for. Default data, one constant and one speed coefficient, for rolling noise are given for each frequency band, 25-10000 Hz, using a logarithmic speed dependence. 80% of the rolling noise sound power is assigned a point source at 0,01 m and 20% is assigned a point source at 0,3 m (passenger cars) or 0,75 m (heavy vehicles). Default data, one constant and one speed coefficient, for propulsion noise are given for each frequency band, 25-10000 Hz, using a linear speed dependence. 20% of the propulsion noise sound power is assigned a point source at 0,01 m and 80% is assigned a point source at 0,3 m (passenger cars) or 0,75 m (heavy vehicles). Rolling noise is corrected for different road surfaces and different air temperatures. It is also possible to correct for wetness, studded tyres and number of axles of heavy vehicles. Propulsion noise is corrected for acceleration/deceleration. All point sources are assigned a specific frequency dependent vertical directivity with the main purpose to take the screening of the car body into account. The lowest point source is assigned a specific frequency dependent horizontal directivity with the main purpose to take the horn effect of the tyre/road source into account. The highest point source for propulsion noise and heavy vehicles is assigned a frequency independent horizontal directivity. Propagation effects are taken into account by giving different acoustic impedances of some different road surfaces.

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