Abstract
This study was designed to investigate the factors which affect the impression of road traffic noise and to find the effective countermeasures to improve sound environment. A preliminary experiment was conducted with 30 different kinds of road traffic noise in order to select sound sources to be used in Experiments 1 and 2. It was found in the preliminary experiment that LAeq showed fairly good correlation with noisiness. However, there were some sounds whose noisiness deviated from the regression line. In Experiment 1 the impression of 10 kinds of road traffic noise was judged using semantic differential. The LAeq values of the sounds were kept equal. It was found that sounds which dominantly consisted of engine noise or exhaust noise were judged as being “shrill” and “powerful”. The impression of “powerful” showed high correlation with loudness level based on ISO 532B and fluctuation strength and the impression of “shrill” with calculated sharpness. The impression of “pleasant” was found to be affected by many factors such as sound pressure level, frequency characteristics and temporal fluctuation of the sound. Experiment 2 was conducted in order to confirm the result of Experiment 1 using the method of paired comparisons. It was suggested that the sound quality was affected by loudness level, fluctuation strength and sharpness. The possible countermeasures to improve the impression of road traffic noise were discussed on the basis of the results of the experiments.
