Vol.1 No.1 2008

22/76

Research paper : Development and standardization of accessible design technologies that address the needs of senior citizens (K. Kurakata, et al.)−19−Synthesiology - English edition Vol.1 No.1 (2008) 4.3 Accommodating individual differenceBased on the investigation in Sections 4.1 and 4.2, appropriate volume setting method for auditory signals could be established by calculating minimum and maximum values of sound pressure level of auditory signals that could be heard in interfering sounds. The last issue remaining was “individual differences”. There were individual differences in human perception. Moreover, individual differences increased with age. Therefore, standard value applicable to the elderly could not be found by simply staring at the average measurement data. The proposed volume setting method could not be accepted as standard method unless it could be proven that it satisfied the characteristics of adequate percentage of the elderly. Therefore, it was necessary to experimentally confirm the possibility of universal application of the proposed method by accurately obtaining various measurement values to estimate the statistical distribution of individual differences.In this study, what percentage of people could hear the auditory signals at which level of volume setting was measured in auditory experiment using several typical home domestic sounds (see Section 4.2). Young people, as well as the elderly, participated in the measurements to compare the differences in hearing characteristics of the two groups. Based on the statistical distribution of the measurement values obtained for the two subject groups, the level of auditory signals that could be heard by adequate percentage (for example 95 %) (minimum value), and the level which was judged “can be heard well” (maximum value) were estimated for each group. As an example, part of measurement results using the maximum value estimate (in case of 1,000 Hz auditory signal) is shown in Figure 5.In this measurement, elderly and young groups rated the audibility of the auditory signal in 5-step evaluation. The marks in the figure show the rating value at about 95 percentile from the top for each group. For example, in the condition marked with “arrow,” 95 % of the subjects in each group responded “4: Can hear well” or “5: Can hear very well” in measurement condition using certain domestic sounds. In another word, response of “3: Neither” or lower was less than 5 %.In this figure, “4: Can hear well” rating values (points above horizontal dash line in the figure) are distributed in the range above 75 dB (vertical dash line in the figure) sound pressure level for auditory signals. That is, in both subject groups, the percentage of subjects who responded “can hear the auditory signal well” at all measurement conditions dropped below 95 % when the auditory signal level was below 75 dB. Conversely, if the auditory signal was above this level, the percentage of subjects who missed the auditory signal would decrease further, but more people would perceive it as being “annoying”, so it was not appropriate as volume of auditory signal of products used daily. Therefore, maximum value of the auditory signal was set at 75 dB. For minimum value, similar estimate was conducted for auditory signals of various frequencies based on the results of the auditory experiment.Overlooking the above analysis results, maximum and minimum values could be set at a certain value in any auditory signal frequency or in any measurement condition using any domestic sound. This confirmed the validity of the auditory model created in Section 4.1. Since the interfering sounds used in the measurements covered almost all characteristics of domestic sounds (Section 4.2), the results of this measurement study should apply accurately to actual domestic situations.The experiment inevitably increases in scale as measurement data are analyzed statistically to address individual differences. In fact, Figure 5 is based on total 5,600 items of data for 80 elderly and young subjects listening at 70 different condition types. Such large-scale measurement result is the basis for setting the minimum and maximum values for auditory signal volume[15, 16].5 Volume setting method for auditory signal by JIS S 0014 Based on the above study result, the volume setting method for auditory signala as described in JIS S 0014 was prepared. The procedure is shown in Figure 6.First, the sound pressure levels of auditory signal prototype and domestic sound generated in the situation where the product in which the signal will be used (for example, sound of water running in sink if the product is used in kitchen) are measured [Figure 6 ①]. Second, the sound pressure levels of Fig. 5 Example of rating result to obtain maximum value for auditory signal (for 1,000 Hz auditory signal).〇: Elderly group ×: Young groupRating scale value of subjectsSound pressure level of auditory signal (dB)5: Can hear very well4: Can hear well3: Neither2: Cannot hear well1: Cannot hear at all2030405060708090100

※このページを正しく表示するにはFlashPlayer9以上が必要です