Motor Vehicle Noise Assessment by Semireverberant Testing

The feasibility of a new approach to vehicle noise monitoring, providing an effective alternative to “side‐of‐the‐road” enforcement is under study. This new approach involves the measurement of vehicle noise in the semireverberant environment of Motor Vehicle Testing stations. Initial studies have shown that the reverberant amplification can be predicted from the room constant. Comparisons between semireverberant and freefield measurements show that the same noisiest vehicles can be identified under both test conditions. Modal patterns have little effect on A‐weighted indoor readings. Tests are continuing to evaluate other factors including changes in the frequency spectrum, consistency of the room constant, selection of engine speed, and the importance of engine load. The statistical distribution of the noise levels from a large sample of vehicles is being recorded to determine levels for legal limits.