Study of Volume Limit for Hearing Protection in the Music listening

In this paper, the mobile diffusion of music player in order to prevent hearing loss, we evaluated whether to be able to lower the volume to a safe level at such a rate as not to be noticed by the listener. Subjects consisted of seven young people and five elderly. The optimal listening level was measured and first used a portable music player to grasp the daily volume the subjects listened to music. As a result, it was discovered that seven out of the twelve listened to volumes greater than 80dB. Based on this result, reaction time was measured due to the difference in attenuation amount per unit time (decay rate). As a result, without being affected by changes in decay rate, youth in the range of 12 dB ± 4 dB, the elderly were found to have noticed the change in volume in the range of 13 dB ± 4dB.


INTRODUCTION
In recent years, portable music players have been spreading due to the convenience of being able to carry music anywhere.Hamamura et al. (1), it revealed that the questionnaire in order to determine the actual usage of the portable music player, done in student 72 people of 26 years from 18 years, 70 people were owned anything like one of the portable music player.In addition, according to the usage of each generation of portable music player through the Internet Research (2), it has been available to those most in their teens and twenties, using better of about 50% in from the 30s 50s We have been hear about you are.Any of the report also shows the height of the utilization of a lower layer of age, listening to music using a portable music player, it can be seen that has become a fairly routine thing for young people.The future, with the aging of such young people, the increase in the elderly of the portable music player usage is also expected.However, on the other hand, is listening to music spanning a long period of time in excess volume has been pointed out that there is a danger that lead to hearing loss (3)(4).In fact, in the EU and WHO, an index that summarizes the listening time of the relationship between the dangerous sound pressure level it has been published.According to it, the European Union (EU), in the case of the sound pressure level 80dB, it is described as at risk for carrying out the hearing loss music listening 40 hours a week.Furthermore, the World Health Organization (WHO), it is pointed out that there is a risk of hearing loss in the case of performing the music listening more than one hour continuously for one day at a sound pressure level 85dB or more.In addition, WHO, the young people of more than one billion people in the world have announced that in the face of fear to become a hearing loss by listening to loud music.However, in Japan, since measures by listening to music at dangerous levels compared to other countries is insufficient, it is necessary to raise awareness of more measures.So, we will, if it is listening to music at dangerous levels, it is possible to reduce the volume at such a rate that the listener will not notice, thought to be useful if you can prevent hearing loss.So far, consideration has been such as music listening time optimum listening level (1), there has been no study on whether reducing the volume people notice at what speed.
In this study, we measured the optimal listening level in order to understand how loudly the user (young, elderly people) listens to music on portable music player.More we measured level difference until the user notices (difference of perceived attenuating level) as well as reaction time until the user notices when sound volume was gradually turned.
as well as reaction level and the reaction time were measured.

Measurement Of Optimal Listening Level
In this chapter, we measured the volume that subject usually listened to music.

The proposed method
The subjects consisted of seven younger individuals ranging from 22 years old to 25 years old (6 males, 1 female), and five elderly individuals from 72 years old 77 years old (all male).Hearing tests were conducted in advance for all of the subjects; the young people had normal hearing, and the elderly confirmed that they have moderate hearing loss to mild hearing loss.
In the experiment, Western rock, of which a large volume was expected, Japanese rock, Japanese punk, and Western pop were used, totaling six different types of music; five of them including Enka of Japanese pop were used as a stimulus.
The presentation of stimulation, using Apple's iPod touch, was conducted through headphones (SENNHEISER HD205).Furthermore, users of portable music players have been found to have many opportunities to listen to music in a noisy environment.The experiment was carried out in two conditions, a quiet environment and a noisy environment (four).The noise level of the five types of environmental sound is shown in Table 1.After the start of reproduction of the subject, each stimulus sound, I was taught to operate the volume control bar to "just say and feel its size."Adjustment of volume was allowed to increase or decrease until appropriate for each subject.Also, before playback of each stimulus, the volume of the iPod touch was set to the state that music playback sound could not be heard.After the optimum listening level adjusting operation ended, each stimulus was recorded with a dummy head, and the optimum listening level values of the equivalent noise levels were multiplied by the A characteristics.

Experiment result
Five of the mean and standard deviation of the young and the elderly another optimal listening level for the environment is shown in Fig. 1.From Fig. 1, a lot of young people found that the optimal listening level was greater than 80dB.Therefore, when you are listening to music at a level that leads to hearing loss, there is a need to lower the volume.

Difference reaction level and awareness time in several attenuation rate
Based on the optimum listening level measurements, when gradually attenuated, the sound volume, the subject and lowering the degree volume were evaluated for perceptibility.

The proposed method
Subjects consisted of the same individuals who participated in the measurement experiment of the optimum listening level.
An experimental stimulation was used as a stimulus for the six kinds of music shown in Section 2.1.Experimental stimuli started to decay from one point in the song (start time), for the time the four patterns were reduce to 20 dB of the average sound pressure (0.5 dB/sec, 0.3 dB/sec, 0.25 dB/sec, 0.2 dB/sec).It shows the waveform of the time difference of perceived attenuating level of 0.5dB / sec in Fig. 2.
The presentation of stimulation, using Apple's Mac Book pro, was played through headphones (SENNHEISER HD205).
Moreover, in order to reproduce the music while listening in noisy environments, using the station premises used for measurement experiment the optimum listening level, experiments were conducted.Stimulus to play, was presented and set to 85 dB of the A level.When listening stimulation was performed, Kraepelin test was conducted so that it did not concentrate only on the listening of the presented music.Then, to measure the final level, the stimulation noticed changes from the start (response level) and time (reaction time).

Experiment result
Two types of songs attempted twice the data in the seven young individuals (28 samples), as the target in Fig. 3 (a) shows the mean and standard deviation of all subjects, all sample results for attenuation perceived difference of perceived attenuating level and it shows the standard deviation.Two types of songs (youth and similar songs) attempted twice the data (20 samples) with the elderly five as the target in Fig. 3 (b) , the mean value of all subjects all sample results for attenuation perceived sound pressure level and it shows the standard deviation.The vertical axis shows the attenuation perceived sound pressure level, the horizontal axis shows that the speed sound pressure level is attenuated between the 1s (the decay rate).
From Fig. 3 (a), it can be seen that there is approximately a 12 dB attenuation perceived sound pressure level regardless of the rate of decay.In addition, when viewed only by the standard deviation, there was seen dispersion of about ± 4dB.In view of this variation, it can be said to have been perceived in the range of approximately 12 dB ± 4 dB from  2, it was perceived that approximately 13 dB ± 4 dB in range is from the start of decay.The cause of variation this time is considered to be due to the difference of feeling the ease of every influence and subject by the melody.When comparing the results of Fig. 3 (a) and Fig. 3 (b), the better attenuation perceived sound pressure level of the elderly is seen to be at a higher tendency than the younger people, which is considered to be due to the hearing level difference.
Then, Two types of songs attempted twice the data in the seven young individuals (28 samples), as the target in Fig. 4 (a) shows the mean and standard deviation of all subjects, all sample results for reaction time.Two types of songs (youth and similar songs) attempted twice the data (20 samples) with the elderly five as the target in Fig. 4 (b) , the mean value of all subjects all sample results for attenuation perceived reaction time and it shows the standard deviation.Compared to the results of Fig. 2, it is considered as being delayed reaction time as the attenuation rate becomes slow in Fig. 4 is the difference between the time taken to reach the attenuation perceived level difference.

Conclusion
For this study, This study, many young and in some Elderly people, measurement of optimal listening level under noise has been found to have exceeded 80 dB.Also, difference of perceived attenuating level in the case of attenuated at the volume that does not notice the person is, regardless of the attenuation rate is about 12 dB ± 4 dB in adults, is perceived in the range of about 13 dB ± 4 dB in the elderly thing is I found.
In the future, it is planned to carry out the study by focusing on high melody, which is likely to have an impact on the variation.

Fig. 1 .
Fig. 1.The optimal listening level of each noisy environment and standard deviation

Fig 3 .Fig 2 .
Fig 3. Relationship between difference of perceived attenuating level and attention rate

Table 1 .
Noise level (dB) of each sound