Soundscape characterization of three public parks of Lisbon Ricardo António Rodrigues ricardo.a.rodrigues@tecnico.ulisboa.pt Instituto Superior Técnico, TU Lisbon, Portugal July 2015 Abstract Noise is a characteristic problem of cities due to the urbanization and industrialization, thus affecting human health and people s well-being. The urban green spaces are places that allow the citizen to contact with nature. In addition to fact that these spaces provide a more pleasant sound environment and maintaining ecological balance in the urban tissue, they also enrich the city providing dynamism and diversity. This work was developed on the theme of soundscape of public parks in Lisbon, intending to make an objective acoustic characterization and subjective one. The latter subdivided in surveys and measurement of masking levels of sound sources in the anechoic chamber. The results of acoustic characterization of the parks showed that in general the sound levels are above the limit imposed by national law. The measuring points which were registered the highest sound levels were along the park's perimeter, next to the roads, showing the impact of road traffic noise in the soundscape of these public spaces. On the contrary, the lowest sound levels were measured in central areas inside the parks. The survey results showed that in a comprehensive manner, the visitors are satisfied with the visual aspects and the sounds emanated inside the parks contrasting with the displeasure shown to transport noise. Masking tests allowed a better understanding of the phenomenon of auditory masking, highlighting the difficulty in masking sound sources with tonal characteristics. 1. Introduction The studies of soundscape began in the late 60 (Schafer, 1977). The research group World Soundscape Project led by Murray Schafer devoted to the study of the sound environment and the influence of the human community. It is in the book entitled "The Tuning of the World," published in 1977 that Schafer defines the concept of soundscape. According to the Scahfer, soundscape defines a set of sounds heard, encompassing sounds that are pleasant and unpleasant. As a musician and composer, the first works of Schafer were based on the relationship between the ear, people and the listening environments (Zhang & Kang, 2007).
Since the introduction of the concept of soundscape proposed by Schafer in the 1970s (Schafer, 1977), many projects and studies have mainly dealt with the perception of the acoustic environment in contexts (Brambilla et al., 2013). The soundscape approach treats the acoustic environment as a multidimensional entity composed of several sound sources, where some of them may have an increase and decrease effect in the overall quality of the sound environment (Nilsson & Berglund, 2006). Cities are places where the sonic environment is diverse. According to Fortuna (1999), in the middle of urban sound entropy, the sounds are characterized by its ambiguity and no single identity but rather various identifications. Each country or city has its own soundscape (Bento Coelho, 2010). In cities where the sound environment is quiet, it can be interpreted as dull and uninteresting by southern populations that enjoy mild and hot climates. Despite the noise being part of the sound composition of cities, can be also interpreted as an indicator of economic power (Schafer, 1977; Bento Coelho, 2010). Although this can be subjectively perceived by citizens as a positive factor in the urban soundscape because noise can be associated with a thriving and dynamic city An application of the soundscape approach in urban tissue is the case of green spaces like public parks. Since nature plays an important role in human health and well being, public parks play a vital health-promoting role by ensuring people s contact with nature scene (Brambilla et al, 2013). Temperature-wise, these spaces play an important role in the reducing the temperature by intervening in heat convection, the transmission radiation and the air infiltration rate. It s also important to highlight the contribution of these areas to reduce noise levels from road traffic and noisy activities (Andersson et al., 1984). The vegetation acts as an acoustic barrier, attenuating noise. Though the ability of the vegetation have in reducing noise is dependent on its length, density and height (Haverbeke & Cook, 1977). Urban green spaces are extremely important because they valorize in many ways the urban space. The different changes that vegetation suffers during the year enrich the city providing dynamism and diversity. 2. Methodology 2.1 Acoustic measurements The equipment used in the field of work related to acoustic measurements was a Bruel&Kjaer sound level meter and a tripod. Some major considerations were taken: - In terms of weather conditions, acoustic measurements weren t performed in rainy days.
- Due to the daily seasonality in terms of sound emission of certain localized sound sources in the parks, the acoustic measurements were performed in the period between 11:00 AM and 17:00 PM. - For all acoustic measurements the sound level meter was positioned 1.5 meters above the ground. The implemented height corresponds to the average height of the human ear. It was also ensured that the placement of the tripod wouldn t affect the circulation of people. - Measurement sites were strategically chosen in order to measure the sounds of certain localized sound sources in the parks (playground, water fountain). 2.2 Socio-acoustic surveys A system of personal interviews in the three gardens was adopted, where the process of selection of respondents was random. The respondents were asked to volunteer and contribute to the research. Preceding the beginning of each survey the respondents were informed that the survey intended to examine the overall quality of the park, thus avoiding induced responses (Szeremeta, 2010). Because the term noise adopts a negative connotation, this was replaced by sound and sounds in order to preserve the neutrality of the respondent s answers. Structurally the questionnaire is divided into three distinct parts. The first part consists of three questions of closed-ended questions, dedicated to the study of the frequency, length of stay and the reason that people visit the garden. a) How often do you use this park? b) How long do you usually stay in the park? c) What is the reason for your visit / stay? The second part of the survey aimed to study the overall quality of the garden. This section includes a total of four questions. 1 - In terms of infrastructure and facilities, how do you assess this park? 2 - In terms of beauty (visual aesthetics) of the park, how do you rate it? 3 - What is the most enjoyable aspect of this park? 4 - What is the most unpleasant aspect of this park? The third part of the questionnaire aimed at the study of the sound perception. This section consists of seven questions where six of them are closed-ended questions (5,6,7,8,9,10) and a mixed question (11). 5 - To what extent do you hear the five types of sounds present in this park? 6 - Which of these sounds you consider pleasant 7 - Which of these sounds you consider unpleasant?
8 - How do you evaluate the atmosphere of the park in terms of sound volume? 9 Does this volume bother you? 10 - How do you evaluate the atmosphere of the park in terms of tranquility? 11 Does sound quality changes when you enter or leave the park? In what aspect? The last section of the questionnaire was devoted to the identification of the respondent (gender, age education and occupation and residence place) 2.2 Masking levels of sound sources This experiment was carried out between 13 and 25 May 2015. The organization of the equipment in the anechoic chamber and its connection to other devices placed outside the chamber are represented in the following scheme (figure 1). Figure 1: Schematic representation of the equipment organization The equipment placed inside the anechoic chamber lie within the rectangle, where the numbers (1) and (2) correspond respectively to the sound level meter and two loudspeakers. The equipment external to the anechoic chamber was the noise generator (3), a measuring amplifier (4) and a laptop (5). The procedure and control system was carried by two researchers. Before the masking experiment, the whole system was calibrated. The communication between the two researchers was made by intercommunication device. After setting the sound source to be masked, the controller played the sound of the recording and, gradually, the white noise was introduced. The masking level was achieved when the white noise did not allow further identification of the defined sound source by the auditor. At this moment, the auditor warned the controller that he would perform the measurement of the masking level. When the measurement finalized, the result was communicated to the controller to note the value. The same procedure was applied to the remaining masking tests.
3. Objective acoustic analysis 3.1 Príncipe Real Park The acoustic measurements of Principe Real park were accomplished in November of 2014, in slightly overcast sky. For the acoustic analysis of this garden a total of 5 acoustic measurements were made where two of them were held inside the park. Figure 2: Acoustic measurement sites at Príncipe Real Park Measurement site Table 1: Description of the acoustic measurements L Aeq (db(a)) Description 1 56,8 Water fountain sounds 2 66,3 Road traffic noise 3 60,3 Road traffic noise 4 61,3 Playground sounds 5 56,4 Road traffic noise 3.2. Estrela Park The acoustic measurements of the sound environment of Estrela Park were accomplished in November in slightly overcast sky. For the acoustic analysis of this garden a total of seven acoustic measurements were made.
Figure 3: Acoustic measurement sites at Estrela Park Measurement site Table 2: Description of the acoustic measurements L Aeq (db(a)) Description 1 67,5 Youth sports activities 2 59,5 Animals and fountain sounds 3 65,1 Sounds form childrens playing 4 59,0 Water foutain and conversation sounds 5 58,2 Playground sounds 6 73,0 Road traffic noise 7 66,6 Road traffic noise 3.3. Calouste Gulbenkian Foundation Park The acoustic measurements of the sound environment of Calouste Gulbenkian Foundation Park park were accomplished in November in a slightly overcast weather. For the acoustic analysis of this garden a total of nine acoustic measurements were made. Figure 4: Acoustic measurement sites at Calouste Gulbenkian Foundation Park
Table 3: Description of the acoustic measurements Measurement site L Aeq db(a) Description 1 73,2 Road traffic noise 2 69,1 Road traffic noise 3 66,8 Water fountain 4 64,3 Water fountain and passage sounds 5 65,5 Ventilation equipment noise 6 54,6 Conversation sounds 7 53,2 Conversation sounds 8 67,3 Road traffic noise 9 67,4 Road traffic noise 4. Subjective analysis 4.1 Socio-acoustic surveys The main results of the questionnaires are depicted. The acronyms JPR, JE and JFCG stands respectively for Principe Real park, Estrela Park and Calouste Gulbenkian Foundation Park. Overall, the results showed that most of the respondents live in Lisbon and belong to the working class. Also most of the respondents visit the parks between two to seven days a week for periods less than an hour. They appreciate the park as a whole instead of a single aspect. Figure 5: Results of the question regarding the motive of visiting the park
Figure 6: Results of the question regarding the aesthetics of park Figure 7: Results of the question regarding the preference of pleasant sounds Figure 8: Results of the question regarding the preference of unpleasant sounds
Figure 9: Results of the question regarding the tranquility of the park. 4.1 Masking levels The masking of tests for further elaboration of audibility maps only served to better test the methodology. However the aim of this experiment girded only the determination of masking levels of sound sources. Due to the extensiveness of the results, the same are not shown in this article. 5. Discussion and Conclusion In the urban space, reducing noise levels have been achieved through the application of preventive and corrective measures but however this strategy is not always feasible and doesn t ensure a better quality of life for the citizens. The soundscape approach is a paradigm shift, emphasizing the strategic role of green spaces in the preservation and promotion of natural soundscape in urban areas. Given the importance of the sound aspect of green spaces, this work aimed to characterize the soundscape of three public parks of Lisbon. Some interesting conclusions were drawn. The results of objective acoustic characterization of the parks indicate that in general, the sound levels are above the limit imposed by the legislation. The highest sound pressure levels were located on the perimeter of the park, closer to the roads, showing the impact of the sounds associated with road traffic in the soundscape of these parks. Globally, lower sound pressure levels were measured inside the parks. With thes in mind, the results showed a variation of sound levels between the parks perimeter and central areas. An interesting case of this variation was found in Calouste Gulbenkian Foundation Park, where the variation was the highest of the three parks. The sound levels from Augusto Aguiar Avenue, Berna Avenue and Marquês Sá da Bandeira Street were measured at 69.1 db (A), 73, 2 db (A) 67.4 db (A) respectively. For these values and the lowest sound level measured inside the garden (L Aeq =53,2 db(a)), the variation ranged from 14.2 db (A) to 20 db (A). The largest value of this
variation is due not only to the distance between the two measurement sites but the presence of the infrastructures of the Calouste Gulbenkian Foundation which acts as an acoustic barrier. The presence of natural elements in the parks, such as water sources, birds as well as quieter interior areas, help reduce the perception of noise associated with urban dynamics and creating more pleasant sound environment. This corroborates with the aim of the use of public parks, where people come to relax and reach psychological restoration (Bento Coelho & Lobo Soares, 2011). Given that the acoustic analysis aims to the physical measurement of sound, the results of the questionnaires showed that the perception of sounds is not solely limited by their intensity. In terms of the visitor s profile, the results showed that the parks are mostly frequented by a population older than 30 years living in Lisbon. Most of the respondents visit the parks two to seven times a week for a period less than 1 hour. This may suggest that people prefer to use the main circulation paths of the parks to get from one place to another. It s important to highlight the visual aspects, since the perception of the quality of gardens results from the interpretation of the different senses. Although some signs related with lack of maintenance and vandalism in the parks were observed, the majority of respondents expressed their satisfaction with the quality of infrastructures and the aesthetics. For the three parks, emphasis was given to transport noise as an unpleasant aspect. These results corroborate with the conclusions drawn from the results of the acoustic analysis. On the other side, the natural sounds took a positive connotation by the visitors. Overall, regarding the sound volume, the visitors consider it normal, and remained unbothered by this volume. This may indicate some compliance to the volume of the sounds, regardless of sound typology. The results regarding the tranquility of the parks showed that visitors are satisfied. However these results can be inconsistent based on the definition of tranquility, whose meaning is related to serenity, peacefulness and quiet. This lack of consistency may be associated with the low specificity of the question and the way this question has been addressed to visitors. Most visitors felt that sound quality changes when they enter or leave the parks. This change may be related because of the presence of certain pleasant sound sources (birds, fountains and water passages, etc.) can mask partially or completely the sounds that decrease the quality of the soundscape. Regarding the masking levels of sound sources, it was noted the difficulty in masking signals with tonal characteristics. This difficulty has been felt particularly in masking sound sources that build the soundscape of Estrela Park. Sounds of the peacock, children playing and the ringing bells of the Basilica were the most difficult to mask.
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