Influence of the frequency of sound pressure level on subjective loudness for a certain length of noise

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In this study, we performed two subjective evaluation tests to obtain factors that affect subjective loudness for environmental noise having a certain duration. In the first experiment, a subjective loudness evaluation was performed using road- and rail-traffic noises having durations of 10 min. As the result, rail-traffic noise was evaluated as being softer than road-traffic noise, although LAeq of the rail-traffic noise was larger than that of road-traffic noise. Rail-traffic noise had longer duration of the low sound pressure level (SPL) and a short, higher SPL peak than road-traffic noise, and we concluded that the factor of the subjective loudness difference depended on the difference in the low SPL frequency. In the second experiment, subjective loudness evaluations were performed using road-traffic noise and modified road-traffic noise. In the modification, the SPL frequency of the road-traffic noise was changed to be similar to that of rail-traffic noise. As the result, the modified road-traffic noise was evaluated as being softer than the original road-traffic noise. In summary, the subjective loudness for a certain length of noise was found to be affected by the frequency of the SPL, and when noise has a long, low SPL duration, it is evaluated as being softer.