Estimation of sound pressure level emitted by a vehicle in the coast-by test from the sound power level obtained in laboratory tests

Abstract

Body of the abstract Tyre/road sound emissions have been proved to be the main source of noise caused by road traffic when driving at medium and high speeds. Tyre/road noise has been widely studied among the last decades. However, an important part of this research has been focused, mainly, on track tests. Different track or road methods have been developed for measurement of tyre/road sound emissions. The most important ones are the Coast-By, the Close-Proximity, the Statistical Pass-By or the Controlled Pass-By methods. Among all of them, the Coast-By method has been raised in Europe as standard method concerning the approval of tyres with regard to tyre/road sound emissions as preconized in UNECE Regulation 117. However, all the above mentioned methods have several disadvantages such as the influence of environmental factors, the different results that can be obtained depending on the test track or the vehicle upon which the tests are carried out, the lack of repeatibility or, the most important aspect, which is the limitation of the measured magnitude, the sound pressure level. A new methodology based on drum tests and the ISO 3744, which was developed in order to avoid these limitations, has been proved to be comparable to the Coast-By (CB) method. This paper describes how to estimate the results of the CB test using the new Drum test method. This new methodology obtains the sound power level of a tyre in Drum test conditions, as an individual source, and uses a standardized soundpropagation method to estimate the sound pressure level under CB track test conditions.