1978-01-01

Relation Between Passby and Stationary Near-Field Noise Measurement of a Passenger Car 785065

Measurements were carried out with a few samples of one type. Nevertheless, as conclusions are based on a given type or at most on a group of motor-noisy passenger cars, it can be taken for granted that conclusions are valid also for a wider range of road vehicles.
Results of full-throttle acceleration passby measurements are governed mainly by engine noise, the contribution of rolling noise being negligible. This means that, as intended, type approval test can be used only to assess noise emission of a car under relatively rare circumstances, existing mainly in urban traffic.
The noise radiation pattern of a car in motion can be approximated in horizontal plane by a circle with acceptable error. This can be important especially for traffic noise prediction methods.
The noise emission of a front engine car can be approximated by the results of the stationary near-the-exhaust measuring method only under operating conditions of fast variation in engine speed, unless, the exhaust system is defective or utterly deteriorated. It has been show that~in accordance with the intention of the standard /3/~the state of repair of the exhaust system can be assessed both from runup and deceleration measurements. This means that stationary near-the-exhaust measurements are appropriate means for vehicle monitoring.
Distinct similarity has been found between passby and stationary near-the-engine measurements when consistent operating conditions were maintained. This suggests that also some degree of correlation between the results of standard measurements exists if the data are restricted to certain types or samples of only one type. The research work so far performed does not enable for setting up quantitative formulation of the question.

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