The test method requires an acoustical environment which is only obtained in an extensive open space. Such conditions are usually provided for during: measurements of vehicles for regulatory certification; measurements at the manufacturing stage; measurements at official testing stations
The results obtained by this method give an objective measure of the noise emitted under the specified conditions of test. It is necessary to consider the fact that the subjective appraisal of the noise annoyance of different classes of motor vehicles is not simply related to the indications of a sound measurement system. As annoyance is strongly related to personal human perception, physiological human condition, culture, environmental condition there is a large variation and therefore not useful as a parameter to describe a specific vehicle condition.
Spot checks of vehicles chosen at random are rarely made in an ideal acoustical environment. If measurements are carried out on the road in an acoustical environment which does not fulfill the requirements stated in this document, the results obtained may deviate appreciably from the results obtained using the specified conditions.
