Proceedings of Meetings on Acoustics

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Proceedings of Meetings on Acoustics Volume 19, 2013 http://acousticalsociety.

1 Proceedings of Meetings on Acoustics Volume 19, ICA 2013 Montreal Montreal, Canada 2-7 June 2013 Noise Session 3pNSc: Joint Poster Session on Noise and Architectural Acoustics (Poster Session) 3pNSc12. Effects of age on feasible sound level of possible warning sounds for quiet vehicles Katsuya Yamauchi*, Takayuki Shiizu, Fumio Tamura and Yuichiro Takeda *Corresponding author's address: Nagasaki University, Bunkyo 1-14, Nagasaki, , Nagasaki, Japan, It has been noted that reduced noise can also lead to potentially dangerous situations for pedestrians because electric and hybrid vehicles are quieter than conventional internal combustion engine vehicles. Hence, the use of warning sounds which are radiated by the vehicle to alert pedestrians is being considered by various governments. To design the sound itself or to develop the regulation concerning the sound, it is much important to know the feasible sound level of the warning sounds compared to the background sounds. Pilot studies on this topic were performed by Yamauchi et al. in 2011 with young subjects. This present study was aimed to reveal the effect of age on feasible sound level of warning sounds. In the experiment, level of five possible warning sounds was adjusted in three different urban environmental sounds in a laboratory. Thirty subjects aged from 19 to 74 years old participated in the experiment. The subjects were asked to adjust the level of warning sounds so that they are clearly audible or just audible depends on the instruction. Results of the adjustments are presented and compared to current recommendations for sound levels of warning signals in quiet vehicles. Published by the Acoustical Society of America through the American Institute of Physics 2013 Acoustical Society of America [DOI: / ] Received 22 Jan 2013; published 2 Jun 2013 Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 1

2 INTRODUCTION Vehicle sounds have been regarded as a noise in urban environments and its levels have reduced by decreasing upper limit regulations of vehicle noise and developping related technologies. On the other hand, for pedestrians, vehicle sounds are also an information source to recognize and estimate a vehicle s behavior. The reduced noise can lead potentially dangerous situations for pedestrians when an oncoming vehicle is inaudible over the background noise[1]. The vehicles that are propelled in whole or in part by electric motors, such as electric or hybrid electric vehicles (EV/HEV), are becoming common in urban fleets. Number of these vehicles is expected to increase following the social demands of greenhouse gas reduction and the realization of a low-carbon society. These vehicles are usually quieter than conventional internal combustion engine vehicles (ICEV), especially when they are driven at slower speed. That is regarded as a problem of vehicle quietness by some governments and the automotive industory. That is of particular concern to the blind community[2][3]. As a measure to the problem of vehicle quietness, installation of a warnign sound to alert pedestrians has been discussed in various governments. The Japanese Ministry of Land, Infrastructure, Transport and Tourism (MLIT) have formulated a guideline for the measure against the quietness problem[4]. The guideline says that a warning sound should automatically emitted when the vehicle is driven at a speed of less than 20 km/h, that the sound should be a continuous sound that evokes the running condition of a vehicle, and that the sound level should not exceed the level of ICEV running at a speed of 20 km/h. Some Japanese automobile manufacturers launched warning systems for their EV/HEV which confirm to the guideline (e.g. [5]). In the United States, the Pedestrian Safety Enhancement Act of 2010 was approved, which was going to establish performance requirements by 2014 for an alert sound that allows blind and other pedestrians to reasonably detect nearby EV/HEV. To harmonize these actions, UN/ECE/WP29/GRB (Working Party on Noise, World Forum for Harmonization of Vehicle Regulations) has established an Informal Group for Quiet Road Transport Vehicles (IG-QRTV). The group has formulated an international guideline based on the Japane guideline[6] and now is going to develop a Global Technical Regulation (GTR) for acoustic requirements of quiet vehicles. Note, however, that the problem can be regarded as a variation of traditional problem such as a masking of a key information sound by the other noise source[7]. Moreover, according to the result of a questionnaire survey on the sound of quiet vehicles[8], 51.6% of respondents who drove their own car daily answered yes to the question that have you ever felt danger or unsatisfaction due to pedestrians unawareness of your driving car? even though all the respondents owned and drove an ICEV except only two who drove HV. These mean that an imitation of ICEV sound cannot be a golden solution to alert pedestrians in urban environments. It is desired to design suitable warning sound that appropreately works as an information, as well as to realize the quiet environment that does not mask even a quiet vehicle sound. Both to develop regulations and to design the warning sound, it is necessary to acquire wide range of knowledge on acoustics. Nevertheless, the acoustical properties of ideal warning sound design, including basic issues such as adequate sound levels, are still not known sufficiently. Though the Japanese and WP29 guideline[4][5] just states that a warning sound should not exceed the sound level of an ICEV running at a speed of 20 km/h, there are not sufficient knowledge whether the sound level is enough to work as a warning in urban sound environment. Concerning that issue, Yamauchi et al.[9][10] showed that a quantitave information on feasible sound level of the warning sounds for quiet vehicles through a psychoacoustic experiment using environmental sounds and possible warning sounds binaurally recorded. The results showed that the feasible sound levels were comparable to noise level of the environment (in L Aeq ), were affected by sound quality of warning sound, and were not different significantly between German and Japanese subjects. However, the most of subjects participated in those experiments were in their 30 s or 40 s. It is well known that the hearing ability decreases as their age. To confirm the effect of age on the feasible sound level of the warning sounds, in this paper, we examined feasible sound levels with subjects in wide age range. Moreover, the previous studies was started before the guidelines were published, hence some of the warning sound stimuli were not meet to the guideline. For the present experiment, the warning sound stimuli were re-designed taking account of the guidelie. Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 2

3 EXPERIMENTAL METHOD Stimuli Three environmental background sounds recorded in Japan were used as background stimuli; on a shopping street with sounds of crowds and shops, on a back street in downtown including traffic noise from distant streets, and in a suburban parking area including sounds of birds and insects. The recordings were performed binaurally using a head and torso simulator (HATS). The A-weighted equivalent sound levels (L Aeq ) were also measured simultaneously with the recording. The measured sound levels and road environmental conditions are shown in TABLE 1. Five potential warning sounds were used in this study as target stimuli. Each target stimulus was designed to exceed the level of the target loudness curve at least one 1/3-octave band when the stimuli played at 55 db(a). The target loudness curve was determined from the ISO-532B loudness curve of the background stimuli. Each potential warning sound was played back over a loudspeaker in an anechoic room and recorded binaurally via the HATS to simulate an assumed relative position between the pedestrian (subject) and the vehicle providing warning sounds from 2m diagonally behind the subject which illustlated in FIGURE 1. TABLE 1. Noise level and environmental conditions of each background sound stimulus. ID Noise Level (L Aeq ) [db] Outline Env Env Env Shopping street (sounds of crowds, sounds from shops) Back street in downtown (traffic noise from distant streets) Suburban parking area (sounds of birds and insects) FIGURE 1. Assumed relative position between the pedestrian and the vehicle providing warning sounds. Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 3

Set-up and Procedure The experiments were performed in a soundproofed room. The experimental setup is shown in FIGURE 2. The signals were presented over Sennheiser HD-650 headphones.

4 Set-up and Procedure The experiments were performed in a soundproofed room. The experimental setup is shown in FIGURE 2. The signals were presented over Sennheiser HD-650 headphones. The input voltage to the headphones was measured, so that, taking into account the headphones sensitivity, the playback level could be calibrated. Subjects could adjust the level of the warning sounds using a slider of a sound mixer. The adjusted level was recorded with a sound recorder. The presented sound level of background stimuli were configured to same level with the recording. FIGURE 2. Experimental set-up. First, one of the background stimuli was presented, and then, approximately 10 s later, one of the warning sounds was overlapped. The subjects were asked to imagine that they were on a road and that the vehicle providing the warning sound positioned 2 m behind them diagonally backward right, as shown in FIGURE 1. There were two tasks in each experimental session. One task was to adjust the warning sounds so that they were clearly audible and could be reliably recognized in the background noise even without concentrating. The other task was to adjust the warning sounds so that they were just audible in the background. The order of these tasks was switched for each new subject. All stimulus combinations were presented once in pseudo-random order. All subjects took two trials for all stimuli combinations for each task. The sound presentation was repeated until the subjects indicating a satisfactory level adjustment. Subjects Thirty Japanese subjects aged between 19 to 74 years old participated in the experiment. The subjects were classified into three age groups (TABLE 2). Two subjects who could not catch the background stimulus and one subject who could not understand the experimental task were excluded form the analysis. TABLE 2. Number of the subjects and their age distribution. Age group Number of subjects (male / female) Age median (min. / max.) Young 10 (5/5) 20.5 (19/24) Middle 10 (6/4) 38.0 (30/48) Older 10 (5/5) 69.0 (60/74) Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 4

5 RESULT AND DISCUSSION FIGURE 3 shows the medians and interquartile ranges of averaged level of two trials for each subjects adjusted level. The adjusted sound levels to be clearly audible and to be reliably recognized in the background noise are indicated as white simbols (as adequate level ), and those to be just audible in the background are indicated as black symbols (as minimum level ). There were no significant difference on the sound levels to be clearly audible between older group and the others. It was expected that the older group requires higher sound level. However, the tendency was not fond. On the other hand, while the minimum sound levels for older group is slight higher than those for young and middle groups. Older people seem to have difficulty to detect the warning sounds in background sounds. The minimum levels to be audible by older group were around 50 db for Env. 1 and 2, which means that some warning sounds in around 50 db at 2 m from the vehicle could not be detected by older people. Env 1 Adjusted Level [db] Env 2 Adjusted Level [db] Adjusted Level [db] Env 3 Adequate Level Minimum Level Noise Level of Environmt Stimuli 35 A B C D E A B C D E A B C D E FIGURE 3. Medians and interquartile ranges of the averaged adjusted levels. (White symbols: warning sounds clearly audible. Black symbols: warning sounds just audible. Horizontal lines: level of environmental background sound). Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 5

6 For Env. 1 and 2, adjusted sound levels to be clearly audible for young group were slightly higher than those for the other groups. The reason of this difference may include a supposition of masking effect by using headphone audio device. After the experiment, some subjects in young age group reported that they adjusted the warning sound louder to be audible even while they were listening to music via headphone on a street. Hamamura[11] has revealed that 97% of young generation in Japan own portable headphone audio device and their average listening level of that was 71.1dB under 63 db, in L Aeq, road traffic noise condition. According to their study, many of young generation reported that they were encountered with danger situation because they did not realize approaching vehicles when they were using headphone audio. The difference found in present experiment is tought to be caused as the result of the supposition of use of the headphone audio devices. According to the previous research results, it was expected that the adjusted sound level would be around the noise level. Nevertheless, the adjusted sound levels for quieter envieonments were higher than their environmental nise levels. In the experimental condition, the subjects were instructed to imagine that they were on a road. That means that when a vehicle comes and goes nearby them, the noise level will increase even in a quieter environment. Comparison between 5 kinds of the warning sounds, the stimulus D was adjusted relatively higher than the others. The frequency characteristic design of warning sounds is thought to be a reason of that. The mean loudness of the initial 5 s for stimulus D was lower than the others. (mean loudness for each stimulus: 8.06, 7.71, 6.60, 4.51, 8.00 sone.) The stimulus D had only one dominant spectrum peak on around 2 khz. Which means that this stimulus could be easily masked by a particular sounds in environmental sound. CONCLUSION The relative quietness of EV/HEV can lead to potentially dangerous situations for pedestrians when an oncoming vehicle is inaudible due to background noise. One possible solution to this problem is the use of warning sounds. To know the feasible sound level of the warning sounds for quiet vehicles, in this paper, we examined feasible sound level with subjects in wide age range. In the experiment, level of five possible warning sounds was adjusted in three different urban environmental sounds in a laboratory. The sound levels to be clearly audible for older subject group were not different from other age groups. The minimum level of older subjects was higher than other. Some warning sounds in 50 db at 2 m from a vehicle, which is similar sound level to an ICEV running at lower speed, could not be detected by older people. Those findings were very important to develop a regulation of warning sound for quiet vehicle that appropreately works as an information for all people. On the other hand, the sound levles to be clearly audible for young subjects was slightly higher. The reason of this increase may include the use of headphone audio device among young generation. It was also revealed that some warning sounds having poor spectral components would be difficult to recongnize in background sounds. ACKNOWLEDGMENTS This study was partially supported by the Japan Society for the Promotion of Science (JSPS), Grant-in-Aid for Young Scientists (A) REFERENCES 1. S. Kerber and H. Fastl, Perceptibility of approaching vehicles in urban background noise, Proc. Inter-noise 2007, CD- ROM (2007). 2. Key Stakeholders Agree on Measures to Protect Blind Pedestrians from Silent Cars Urge Passage as Part of Motor Vehicle Safety Act, (National Federation of the Blind, 2010) (Last viewed 22 Jan 2013). 3. World Blind Union, World Blind Union comments on Japanese guidelines, Informal document of UNECE/WP29/GRB/QRTV, QRTV (2010). 4. Ichiro Sakamoto, Hiroyuki Houzu, Takeharu Tanaka, Kazumoto Morita, Michiaki Sekine, Report on baseline survey for standardization of measures for quiet vehicles in Japan, Proc. Inter-noise 2011, CD-ROM (2011). 5. UNECE World Forum for Harmonization of Vehicle Regulations (WP29), Consolidated Resolution on the Construction of Vehicles (R.E.3), pp (2011). Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 6

7 6. Toshiyuki Tabata, Heather Konet, Tsuyoshi Kanuma, Development of Nissan Approaching Vehicle Sound for Pedestrians, Proc. Inter-noise 2011, CD-ROM (2011). 7. Koji Nagahata, A critique on the quiet vehicle problem from the view point of soundscape study, Proc. Inter-noise 2011, CD-ROM (2011). 8. K. Yamauchi, Yuma Sakabe, Kenji Ito, Sayaka Inoue, Shin-ichiro Iwamiya, Questionnaire survey on the sound of quiet vehicles, Proc. Inter-noise 2012, CD-ROM (2012). 9. Katsuya Yamauchi, Masayuki Takada, Koji Nagahata and Shin-ichiro Iwamiya, An Examination on Required Sound Levels for the External Acoustic Sign for Quiet Vehicles, Proc. Inter-noise 2010, CD-ROM (2010). 10. Katsuya Yamauchi, Daniel Menzel, Hugo Fastl, Masayuki Takada, Koji Nagahata, Shin-ichiro Iwamiya, Cross-cultural study on feasible warning sounds for quiet vehicles, Proc. Inter-noise 2011, CD-ROM (2011). 11. Mariko Hamamura and Shin-ichiro Iwamiya, Survey on the use of portable audio devices and the users attitude toward music and environmental sounds, Proc. Inter-noise 2011, CD-ROM (2011). Proceedings of Meetings on Acoustics, Vol. 19, (2013) Page 7

Detectability and hearing impression of additional warning sounds for electric or hybrid vehicles

Detectability and hearing impression of additional warning sounds for electric or hybrid vehicles Katsuya YAMAUCHI 1 ; Takaichi SANO 2 ; Shin HASEGAWA 2 ; Fumio TAMURA 2 ; Yuichiro TAKEDA 2 1 Faculty of