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Research paper : Development and standardization of accessible design technologies that address the needs of senior citizens (K. Kurakata, et al.)−17−Synthesiology - English edition Vol.1 No.1 (2008) The authors, therefore, addressed the three factors: (i) decreased hearing by aging, (ii) interference by domestic sound, and (iii) presence of individual differences. Then, research was conducted to develop the volume setting method for auditory signals that can be heard readily by both the elderly and the young in actual domestic situations. As a result, JIS S 0014 was proposed and established.4 Issues in development of volume setting method for auditory signalsThere were several issues that had to be solved technologically for the three factors and addressed in developing the volume setting method for auditory signals. The solutions taken by the authors for each issue will be summarized using examples of some measurement results.4.1 Accommodation of decreased hearing by agingThe volume setting method for auditory signal must appropriately accommodate the issue of decreased hearing due to aging. For young people, there is a long history of research on hearing sound in interfering noise, and the model for estimating the hearing level has been established. The sound becomes audible when the target sound level is higher than a certain level against interfering sound. Similarly, for the elderly with decreased hearing, it was assumed that whether the target sound could be heard or not can be estimated based on the difference of sound pressure level (SN ratio) of the two sounds. At that time, however, useful data that measured the least SN ratio needed for the elderly or the difference compared to young people did not exist at all.Therefore, the authors started by measuring the hearing ability in presence of interfering sound for the elderly and young people. Figure 2 shows an example of the results. It can be seen that even under condition of the same interfering sound, the elderly cannot hear the target sound unless it was 5 dB higher compared to young people, and 10 dB for some frequencies in people with severely decreased hearing. From these measurement results, similar level of aging effect in hearing auditory signals in actual environment was anticipated.Next, based on the above basic findings, sound pressure level of auditory signals needed in presence of real domestic sounds must be estimated. The problem was that the interfering sound used in the experiment described in Figure 2 was a relatively simple noise, but domestic sounds fluctuated in both time and frequency. The audibility of signals changed depending on type and scale of change. However, it is not realistic to experimentally investigate the auditory effect of all fluctuations. It was necessary to construct a simplified auditory model based on certain assumptions for a sound detection process.Looking back at the researches in which the authors were involved pertaining to detection of sound from noise[8, 9] and basic research on hearing characteristics[10], it was projected that average energy content, rather than fine time fluctuation in sound, had greater effect on many auditory phenomena. Therefore, it was hypothesized that auditory signals could be heard when the ratio of average volume of auditory signal and interfering noise (SN ratio) surpassed a certain value (this was defined as “minimum value”).Also, the level that could be heard clearly by the elderly with decreased hearing should be attained when the volume of auditory signal was raised above this value. Experimental investigation confirmed that the elderly perceived the sound just as loud as young people when the sound reached a certain level[11]. This sound level was defined as “maximum value”. By setting the sound pressure level of the auditory signal so it would fit between the minimum and maximum values, the model was simplified for designing auditory signals that could be heard at appropriate level even in the presence of fluctuating interfering sound.The validity of the hypotheses as well as maximum and minimum values were investigated and measured by hearing Fig. 2 Sound pressure level necessary for hearing sound in interfering sound (detection threshold).Revised from Reference [7]. Setting young people as standard (vertical axis, 0 dB), relative increase in detection threshold of elderly people is shown.Fig. 3 Range of domestic sounds targeted in domestic sound database JIS TR S 0001[12] and factors considered.250500100020004000151050-5Relative detection threshold (dB)Frequency (Hz)Elderly, severe hearing lossElderly, mild hearing lossYoung…IndoorOutdoorTypes of roomLiving roomBedroomKitchenBathroomJapanese-style roomWestern-style roomSize of roomVolume of sound sourceJapanese-style roomWestern-style roomVariableTarget spaceConstant

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