A soundwalk study on the relationship between soundscape and overall quality of urban outdoor places

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1 A soundwalk study on the relationship between soundscape and overall quality of urban outdoor places Mats E. Nilsson 1, Jin Yong Jeon 2, Maria Rådsten-Ekman 3, Östen Axelsson 4, Joo Young Hong 5, and Hyung Suk Jang 6 1, 3, 4 Department of Psychology, Stockholm University, SE Stockholm, SWEDEN 2, 5, 6 Division of Architectural Engineering, Hanyang University, Haengdang-dong, Seongdong-gu, Seoul , KOREA Abstract: In a field study, we explored the relationship between the soundscape and the overall quality (good bad) of outdoor open places. Thirty three residents in down town Stockholm participated in soundwalks near their homes. Along the soundwalk route, the participants assessed six places with respect to the soundscape, the visual environment and the overall quality of the place using a questionnaire. The six locations were selected to vary in auditory and visual quality. A regression model with perceived auditory and visual quality as predictors explained a substantial part of the variance in assessments of the six place s overall quality. Interestingly, the concordance among participants was greater for overall quality than for visual or auditory quality, which may suggest that it is easier and more natural to assess the overall quality than specific qualities of environments. Keywords: Soundscape, soundwalk, urban environments 1. Introduction The urban acoustic environment is composed of sounds from many sources. The perceived quality of the acoustic environment (soundscape quality) depends on how its sources are perceived in interaction with each other and in interaction with other aspects of the environment, for example the location s visual quality. Simple acoustic indicators, such as the equivalent continuous sound-pressure level, are not sufficient as predictors of soundscape quality in most areas (highly noise exposed environments are possible exceptions). Therefore, methods based on perceptual measurements with humans have been developed (e.g., Berglund & Nilsson, 2006; Gustaviano, 2006; Dubois et al., 2006). The purpose of the present study was to test a soundwalk methodology in which a panel of residents evaluated carefully selected locations in their neighborhood. The method tested in this study was developed from our soundwalk research conducted in Seoul (e.g., Jeon et al., 2011) and Stockholm (e.g., Axelsson et al., 2009). We selected locations in a pilot study, where 1 mats.nilsson@psychologu.su.se 2 jyjeon@hanyang.ac.kr 3 maria.radsten.ekman@psychology.su.se 4 oan@psychology.su.se 5 st200045@hanmail.net 6 janghyungs@gmail.com 1

2 participants freely indicated locations along a route with distinct visual and/or auditory qualities. Based on the result from this study, we identified six specific locations for the main study, in which a panel of 33 residents evaluated the overall, visual and auditory aspects of each location s environment. Thus, apart from testing the soundwalk methodology, the study design made it possible to assess the relationship between overall, visual and auditory qualities of the environments. Such data is needed, because previous experimental studies show conflicting results with respect to the effects of auditory features on overall quality of environments (e.g., Carles et al., 1999; Kuwano et al., 2001; Watts et al., 1999), and few field studies have been reported. 2. Method 2.1 Participants Invitations to participate were sent to 500 randomly selected households in the neighborhoods surrounding the soundwalk area. The invitation letter explained that the participants had to be 18 years or older, and be able to walk stairs. Thirty three participants agreed to participate in the soundwalks, 19 women and 14 men, with a median age of 63 years (range = years). As expected, the sample was not representative of the residents in the area, but consisted of persons with time to participate during week days, particular persons retired from work (18 out of 33 were retired, 1 was unemployed, 10 were employed and 4 were self-employed). 2.2 The soundwalk area For the soundwalks, six locations were selected near Mariatorget on the island Södermalm in down-town Stockholm. The soundwalk area was selected because it includes spots with varying visual and auditory qualities. The six locations were selected from the results of a prior study in the area, in which 8 participants walked along a predefined route and freely chose where to stop and listen to the soundscape or to view the scenery, using a methodology developed by Jeon and collegues (Jeon et al., 2011). A brief description of each location is given below. Location A was on the pavement along the busiest street surrounding park Mariatorget. Location B was at a road intersection in a down town residential area, aligned with apartment buildings. Location C was a vantage point located at the top of a small cliff, with a view over Stockholm city, fairly close to a railway bridge and construction site. Location D was on the same cliff as Location C, but further away from the railway bridge and construction site. Location E was on the pavement at a very busy street corner. Location F was on the pavement along the least busy street surrounding park Mariatorget. 2.3 Soundwalk questionnaire During the soundwalk, the participants filled in a questionnaire. For each of the six locations, the questionnaire contained three sections: (1) A set of questions on the overall environment at the location, including a general question on perceived overall quality, rated on a 5-point bipolar category scale with the response alternatives: Very good, Good, Neither good, nor bad, Bad, and Very bad (coded 2, 1, 0, -1, and -2). (2) A set of questions on soundscape quality of the location. This part included questions on sound source identification (including traffic noise, human sounds, and natural sounds), with the response alternatives Do not hear at all, Hear a little, Hear moderately, Hear a lot, and Dominates completely. It also included eight attributes ( pleasant, chaotic, exciting, uneventful, calm, annoying, eventful, and monotonous ) rated on a 5-point category scale. Finally, a general question on perceived auditory quality was included, which had the same response format as the question on perceived overall quality (see above). (3) A set of questions on the visual aspects of the location, including a general question on perceived visual quality, which had the same response format as the question on perceived overall quality (see above). 2

3 2.4 Procedure and design The soundwalks were conducted Monday to Friday afternoon (13:45 17:15), the last week of October The time of the day was chosen to obtain data collected at about the same time each day, and before the sun set at around 17:30. The soundwalks were conducted in 9 individual sessions with 2 5 participants in each. A soundwalk lasted approximately 60 min. The participants gathered at Mariatorget, and were then guided along a defined route. Thus, all participants assessed the six listening locations in the same order. Before the soundwalk, the participants were briefed about the questionnaire, and asked to conduct the soundwalk in silence in order not to disturb each other. Please observe that the purpose of this soundwalk was not to raise the participants awareness of the urban soundscape, but to measure it. At each listening location, while the participants filled in the questionnaire, the soundscape was recorded for at least 120 s (binaural microphone: B&K, Type 4101; portable field recorder: Zoom, H4n). In total, 9 groups 6 locations = 54 recordings. 3. Results and Discussion Below, we present the results of the soundscape assessments (Section 3.1), followed by analyses of the assessments of perceived overall, visual and auditory qualities of the six locations (Section 3.2). 3.1 Characterization of the location s soundscape Table 1 presents acoustics variables derived from binaural recordings at the six locations. Each db-value is calculated as a mean value from nine recordings (for each binaural recording, the left and right channel were averaged on an energy basis). The acoustic variables are indictors of overall sound-pressure level (L Aeq, L A50 ), background sound-pressure level (L A95 ), low-frequency content (L Ceq L Aeq ) and time variability (L A10 L A90 ). The table also includes percentages of participants who indicated that a given sound source (a) could at all be hard, or (b) was heard a lot or dominated completely. We also characterized the six soundscapes using Axelsson and colleagues circumplex model of soundscape quality (Axelsson et al., 2010). According to this model, each soundscape may be located in a two-dimensional space defined by the orthogonal dimensions Pleasantness (unpleasant pleasant) and Eventfulness (uneventful eventful). Values on these dimensions were calculated from responses on the eight attribute scales included in the questionnaire (cf. Axelsson et al., 2009). Figure 1 plots the soundscapes at six locations in the space defined by their values on Pleasantness and Eventfulness. The soundscape measurements may be summarized as follows. The worst soundscape was found at Location E. It was the noisiest spot (L A50 = 70 db, L A95 = 65 db), and the soundscape was dominated by traffic noise, and sounds from nature was not heard (Table 1). This location had the least pleasant and most eventful soundscape (Fig. 1). Table 1 Acoustic analyses of sound recordings, and questionnaire data on sound source identification Location A B C D E F L Aeq [db] L A50 [db] L A95 [db] L Ceq L Aeq [db] L A10 L A90 [db] Traffic noise [%] 100 / / 3 91 / / / / 21 Fan noise [%] 24 / 0 21 / 0 48 / 6 25 / 0 50 / 9 31 / 0 Other noises [%] 64 / / / / / / 0 Humans [%] 91 / 6 91 / / 0 61 / 0 91 / / 24 Nature [%] 30 / 0 36 / 0 45 / 6 67 / 6 0 / 0 64 / 6 Note. Percentages were calculated from responses on the source identification scales, with response alternatives Do not hear at all, Hear a little, Hear moderately, Hear a lot, and Dominates completely. The first percentage-value in each entry refer to the proportion of respondents who heard a given source (i.e., did not indicate Do not hear at all ), the second percentage-value refer to the proportion of respondents who either responded Hear a lot or Dominates completely. 3

4 Figure 1 Averaged perceived Pleasantness and Eventfulness of soundscapes at the six locations (A F). Values were derived from questionnaire responses on eight attribute scales (cf. Axelsson et al., 2009) The soundscapes at Locations A, C and D were of intermediate quality. These spots were fairly noisy (L A50 = db, L A95 = db), and the soundscapes were dominated by traffic noise or other noises, although other sounds, including sounds from nature, could be heard as well. These soundscapes were assessed as moderately pleasant and fairly eventful. The best soundscapes were found at Location B and F. These spots were not very noisy (L A50 = db, L A95 = db). No particular sources seem to have been dominating these soundscapes, but sounds from human activity and traffic could often be heard. These soundscapes were assessed as pleasant and fairly (F) or moderately (B) eventful. 3.2 Assessments of the location s overall, visual and auditory quality Figure 2 shows median values and interquartile ranges of assessments of the six locations with respect to (i) perceived overall quality (circles), (ii) perceived visual quality (squares), and (iii) perceived auditory quality (diamonds). The six locations are ordered along the X-axis from the worst (E) to the best soundscape (F). Perceived auditory quality was, on average, assessed as lower than or equal to perceived overall quality, whereas perceived visual quality never was assessed as less than perceived overall quality. The profiles for perceived visual and overall quality follow each other closely, whereas the profile of perceived auditory quality was different. This indicates that perceived visual quality of the environments was more important for the overall assessments than perceived auditory quality. However, at two spots (A & D), the perceived overall quality was lower than perceived visual quality, but greater or equal to perceived auditory quality, which is consistent with a detracting effect of the soundscape on perceived overall quality of the environment. Figure 2 Median perceived overall, visual and auditory quality at six locations (A F). Error bars present interquartile ranges. Perceived quality was rated on a bipolar category scale with the response alternatives: Very bad, Bad, Neither good, nor bad, God, and Very god (coded -2, -1, 0, 1, and 2). 4

5 Table 2 Regression analysis with perceived overall quality as dependent variable, and perceived auditory and visual quality as predictors. Auditory Visual Location R 2 β t β t A * B * C * D * E * F * * All *p < t-values were not calculated for the last model (All), because its coefficients were derived from multiple observations per person, which violates the independence assumption of statistical significance testing. We conducted linear regression analyses to further assess the relationship between, on the one hand, perceived overall quality of the locations and, on the other hand, perceived visual and auditory qualities. Analyses were conducted separately for each location, and combined for all six locations. Assuming that the bipolar scales approximate interval-scale measures of perceived quality, we used assessments of perceived overall quality as dependent variable, and assessments of perceived visual and auditory qualities as predictors. Table 2 presents the regression statistics. In general, the standardized regression coefficients (β) were greater for perceived visual than for perceived auditory quality, and the former were in most cases found to be reliably greater than zero. This suggests that participant s assessments of perceived overall quality were influence by the visual environment more than by the soundscape. We also explored how well the participants agreed with each other in their assessments of the location s perceived quality. Each of the 33 participants had their own quality-assessment profiles across the six locations. Figure 3 presents each participant s quality-assessment profile, separately for perceived overall (left), visual (middle) and auditory (right) quality. For each variable, this creates a skein of profiles, which illustrate the similarity of profiles. The profiles appear to be most similar for the perceived overall quality, and least similar for perceived auditory quality. To assess this statistically, the data was organized in three new 6 33 matrices, where the rows represent the six locations and the columns represent the 33 participants. The columns were then intercorrelated (Spearman s rho, r s ), and the similarity of the profiles was assessed as the mean values of all correlations. These analyses suggest that the participants agreed more in their assessments of perceived overall quality (mean r s = 0.67), than on their assessments of specific properties of the locations (mean r s = 0.51 for both perceived visual and auditory quality). This cannot be due to a ceiling effect (less variability near the end of the scale), because the assessments of perceived visual quality were, on average, closer to the upper end of the quality scale than the assessments of perceived overall quality (see Fig. 3). A more plausible explanation is that assessments of perceived overall quality comes more natural, and thereby are easier to make, than assessments of specific qualities of environments, which require the responder to separate those qualities (e.g., soundscape or landscape) from other aspects of the environment. 4. Concluding remarks This soundwalk study illustrates one approach to perceptual measurements of urban outdoor environments. The panel consisted of residents in the soundwalk area, with no prior experience of soundscape measurement. Despite this, their assessments of the soundscapes clearly separated the different locations in a meaningful way in terms of sound source identification, perceived pleasantness and eventfulness, and soundscape quality. Assessment of perceived overall quality was found to be closer linked to perceived visual than to perceived auditory quality of the locations. Interestingly, the concordance among participants was greater for perceived overall quality than for perceived visual or 5

6 auditory quality, which may suggest that it is easier and more natural to assess perceived overall quality than qualities of specific aspects of environments. This result needs to be replicated on a larger and more representative sample. At this stage, we may only speculate whether specific questions on visual or auditory features of environments may artificially force participants to separate aspects they would otherwise consider holistically. Figure 3 Individual profiles of quality assessment for perceived overall (left), visual (middle), and auditory quality (right). Perceived quality was rated on a bipolar category scale with the response alternatives: Very bad, Bad, Neither good, nor bad, God, and Very god (coded -2, -1, 0, 1, and 2). Acknowledgments This research was sponsored by (1) the Swedish Research Council (VR), (2) the National Research Foundation of Korea (NRF), funded by the Ministry of Education, Science and Technology and (3) the European Community's Seventh Framework Programme (FP7/ ) under grant agreement n , collaborative project HOSANNA. References Axelsson, Ö., Nilsson, M. E., & Berglund, B. (2009). A Swedish instrument for measuring soundscape quality, Euro Noise Edinburgh, UK: EAA. Axelsson, Ö., Nilsson, M. E., & Berglund, B. (2010). A principal components model of soundscape perception. Journal of the Acoustical Society of America, 128, Berglund, B., & Nilsson, M. E. (2006). On a tool for measuring soundscape quality in urban residential areas. Acta Acustica united with Acustica, 92, Carles, J. L., Barrio, I. L., & de Lucio, J. V. (1999). Sound influence on landscape values. Landscape and Urban Planning, 43, Dubois, D., Guastavino, C., & Raimbault, M. (2006). A cognitive approach to urban soundscapes: Using verbal data to access everyday life auditory categories. Acta Acustica united with Acustica, 92, Guastavino, C. (2006). The ideal urban soundscape: Investigating the sound quality of French cities. Acta Acustica united with Acustica, 92, Jeon, J. Y., Lee, P. J., & Hong, J. Y. (2011). Design elements of urban soundscape derived from individual soundwalk, Proceedings Inter-Noise 2011, Osaka, Japan: I-INCE. Kuwano, S., Namba, S., Komatsu, M., Kato, T., & Hayashi, Y. (2001). Auditory and visual interaction in the aesthetic evaluation of environment. Empirical Studies of the Arts, 19, Watts, G., Chinn, L., & Godfrey, N. (1999). The effects of vegetation on the perception of traffic noise. Applied Acoustics, 56,