変動騒音のうるささ : 騒音レベルの標準偏差と変動周波数の影響

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The effect of the following two factors of fluctuating noise on the annoyance was investigated by means of fluctuating noise (white noises) artificially generated:One is the standard deviation of sound level (σ), the other being the frequency of level fluctuation which is called 'fluctuation frequency' here. Randomly fluctuating noises of Markoff series type were used as principal stimulus sounds to investigate the effect of σ on the annoyance. The level fluctuation of these sounds (Fig. 1) follows the Markoff process and its correlogram is expressed by an exponential function (Eq. 5). The distribution of sound level was normal, and σ took three values (Table1). The number of stimulus sounds including four steady noises was nineteen. The levels of fluctuating noises were set so that either the arithmatic mean of sound level (L^^^-) can be 70±0. 5 dBA or the energy mean level (L_<eq>) can be 87. 5±0. 5dBA. (when σ≒15 dB and L^^^-≒20 dBA, then L_<eq>≒88 dBA. )Three sounds were generated for each combination of σ and L^^^- or L_<eq>. Test was made by the method of magnitude estimation. Students of both sexes, fifteen each, with normal hearing acuity served as subjects. They were given abundant practice before the experiment, and asked to form their judgments on the basis of the total over-all effect of sounds. The data were first normalized by equalizing the geometric mean judgement of each subject, then the numbers were multiplied by a factor to make his or her estimates for the steady noise of 75dBA average one. From the results for steady noises (Eq. 6, Fig. 2), the average estimate of a sound can be converted into the sound level of steady noise which gives an annoyance equivalent to that of the sound. The level is called here Effective Sound Level(ESL). The experimental result shows that ESL increases with σ when L is constant, but slightly decreases with increasing σ when L<eq> is constant(Fig. 3). ESL is in approximate proportion to L<eq> but is neither in proportion to NPL nor to TNI(Figs. 4-6). Similar experiments were carried out to investigate the effect of fluctuation frequency on the annoyance using sinusoidally fluctuating noise (Fig. 7) and randomly fluctuating noise of the Yule series type (Fig. 10). The level fluctuation of randomly fluctuating noise of the Yule series type follows the Yule process (Eq. 10). The power spectrum of this process has a peak at a frequcncy (f_0) and is cut off in the higher frequency region (Fig. 9). Some of the physical characteristics of the stimulus sounds are shown in Tables 2 and 3. The experimantal results (Figs. 8, 11) show that the fluctuation frequency has little effect on the annoyance over the range from 0. 1 to 1Hz. All the results including those of similar experiment using serrately fluctuating noise are plotted against σ for L^^^-=70 dBA (Fig. 12) and for L_<eq>=88 dBA (Fig. 13). It can be seen again that ESL increases with σ when L^^^- is constant, but does not increase therewith when L_<eq> is constant. High correlation coefficients were found between ESL and L_<eq>, L_<10>, and L^^^-+σ, but the correlations between ESL and NPL, TNI, L_<50>, and L^^^- were found poor (Figs. 14-16, Table 4).
社団法人日本音響学会の論文
1978-07-01

変動騒音のうるささ : 騒音レベルの標準偏差と変動周波数の影響

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