騒音のうるささに及ぼす立上がり速度の効果

抄録

The object of this experiment is to clarify the effect of rising speed of a sound on its annoyance. White noise was used as stimulus sounds whose rising speed ranged from 25 dB/s to 1000 dB/s. The idealized time pattern of signal employed in the judgment test is shown in Fig. 1, and some physical characteristics of the stimulus sounds are presented in Table 1. Ten male and ten female students with normal hearing acuity served as the subjects. They were given abundant practice before the actual experiment began. Subjects were instructed to judge the whole perceived magnitude of the sound, for example, annoyance, unpleasantness and so on. The sounds were arranged at random with respect to test variables and presented to the subjects through a headphone in the sound proof room. Annoyance of sounds thus presented are estimated by the subjects by the method of magnitude estimation. The number denoting annoyance of a sound, the level and rising speed of which were 80 dB and 1000 dB/s respectively, was arbitrarily equated to 1, and the other annoyance estimates for each subject were transformed with reference to this value. The results obtained as shown in Fig. 3 that the annoyance expressed as the logarithm of the ratio of annoyance increases linearly with the logarithm of the rising speed. The following equation was obtained by multiple regression analysis with two independent variables: logψ=0. 0278L+0. 0346R_s-2. 269, where ψ is the ratio of annoyance, L is the peak level (dB), and R_s is the rising speed (dB/s). From the equation, it can be seen that annoyance becomes twice when the level of sound increases by 10. 8 dB (Fig. 4). From this relation, ψ is expressed as the relative sound pressure level (RSPL), which is shown in the left ordinate of Fig. 3. To show the average annoyance increase with rising speed, the results shown in Fig. 3 are averaged and plotted in Fig. 5. However, since acoustic energy of stimulus decreased as the rising speed increases, the results are corrected so that the annoyance increase due to steepening of rising speed can be obtained for equal energy stimulus (Fig. 6). Difference of sound pressure level corresponding to the difference of annoyance between the sounds with rising speeds of 25 dB/s and 1000 dB/s was about 2. 6 dB.