Abstract
Train noise as a nuisance has begun to arouse an increasing public attention, but there are few investigations on the evaluation of train noise. This study aimed at obtaining a quantitative relation of noisiness to level, duration and rise time of train noise. As a result of the psychoacoustical experiments by using simulated train noise, an expression was obtained and it gave a satisfactory explanation to noisiness. The reliability of the expression was verified in turn through rating experiments by using the actual train noise recorded in a magnetic tape. Relations between this expression and other evaluations are also discussed in this paper. The results obtained here are as follows:1)The noisiness change of train noise caused by the variation of its time pattern is based on the change of its total energy. The rate of noisiness change, however, differs according as the energy change is caused by the change of peak level of noise or by the change of its duration, even if the energy changes are equal in both cases(See Fig. 5). 2)As to noisiness the penalty for doubling of duration Td(10dB down duration time)depends on the peak level of noise. The penalty is 1. 2dB for doubling of duration at 60dB(A) peak level, 1. 5dB at 70dB(A) and 1. 8dB at 80dB(A) respectively(See Fig. 6). 3)As an evaluation index representing the contributions of peak level and duration of train noise in the judgment of noisiness, the following N seems to be convenient and reasonable. N=P. L(A)+(P. L(A)-20)/10log_<10>(Td) where P. L(A)is the A-scale peak level and Td is the duration. This index gives a satisfactory explanation to noisiness of actual train noise observed in laboratory experiment. 4)When periodical and pulsive fluctuation appears in the peak level, some numerical correction should be made to N. For a fluctuation period of 1 sec or less we obtain +3dB as a correction by another examination. However, further study should be carried out for many cases.
