The Relation Between the Loudness and the Mean of Energy of Level-Fluctuating Noises

It is very significant to investigate the law of perception concerning the level-fluctuating noises when we consider that the levels of sounds which surround us are fluctuating at any moment. In our previous paper (Namba, et al., 1971) the loudness of intermittent noises whose levels are fluctuating (abbreviated as ‘level-fluctuating noises’) was investigated by matching it with that of level-fixed noises. And the result showed that the loudness of level-fluctuating noises changed corresponding with the mean, L or Lm, of physical intensity of level-fluctuating noises. L and Lm were calculated as follows:Lm=1/nnΣi=1Xi=1/n[nΣi=1(10logIi/I0)]L=10lognΣi=1Ii/I0-10lognWhere Xi is the sound pressure level of each noise which constitutes the level-fluctuating noise. I0 is the reference level (0.0002μMbar), Ii is the value of intensity of each noise and n is the number of constituent noises.In the present experiments we investigated the two problems which remained unsolved: (1) which mean, L or Lm, is more suitable for expressing the loudness of level-fluctuating noises? And (2) what effects does the length of on-time and off-time of intermittent noises have on the loudness of level-fluctuating noises? The method and the apparatus used in the present experiments were just the same as in our previous experiments except that two electronic switches were added in order to control on-time and off-time in Exp. II and III.Exp. I was designed to investigate which of the two means, L and Lm is more fitting. Both noises, level-fluctuating and level-fixed, were composed of 50 constituent noises, on-time and off-time of which were 72msec and 34msec respectively. The levels of constituent noises of level-fluctuating noises were 66, 68, 70, 72 and 74dB SPL in series 1, 66, 68, 70, 72 and 78dB SPL in series 2, 66, 68, 70, 72 and 82dB SPL in series 3, 66, 68, 70, 72 and 86dB SPL in series 4, and 66, 68, 70, 72 and 90dB SPL in series 5. In other words 4 kinds of stimuli in each series were kept at the same level and only the most intense stimulus was systematically changed with the corresponding change of L and Lm. The result showed that the loudness increased in accordance with the change of L and the discrepancy from Lm, was clear.Exp. II and III were conducted in order to investigate the effect of on-time and off-time. In Exp. II the levels of constituent noises were 62, 66, 70, 74 and 78dB SPL, and both on-time and off-time were 50, 100, 200 or 500msec. In Exp. III, for the purpose of the more precise investigation of the effect of the duration, the levels of constituent noises were fixed at 70dB SPL and only on-time and off-time were changed just in the same way as in Exp. II. The results of Exp. II and III showed that the loudness increased as the increase of total on-time during 5sec presentation of intermittent noises and that the loudness was again in good agreement with L when it was calculated as the ratio of total on-time during 5sec. This means that the effect of duration is nothing but the effect of the amount of energy the noise has. Therefore, it may be concluded from these results that the loudness of level-fluctuating noises is expressed by L.There still remain several problems such as the effect of rise and fall time, etc, which must be solved before establishing the definite model.