A prototype of a street furniture element for soundscape management ...

A PROTOTYPE OF A STREET FURNITURE ELEMENT FOR SOUNDSCAPE MANAGEMENT Gioia Fusaro, Francesco D’Alessandro University of Perugia, Department of Civil and Environmental Engineering, Via Goffredo Duranti, 93, 06125 Perugia, Italy email: [email protected]

Jian Kang, Francesco Aletta, Efstathios Margaritis University of Sheffield, School of Architecture, Acoustics Group, Sheffield, Western Bank, Sheffield, South Yorkshire S10 2TN, United Kingdom

Francesco Asdrubali Department of Engineering, University of Rome Tre, via V. Volterra 62, 00146, Rome, Italy In modern urban contexts, there is a growing interest in developing new design solutions for noise-related issues and soundscape design and management. The aim of this study was to develop an integrated design solution to create selective quiet spots in urban parks affected by road traffic noise. Firstly, the acoustic properties of a set of materials suitable for 3D printing were analysed in order to select the one that can provide the best combination in terms of acoustic performance, design flexibility and cost-effectiveness. The results showed that such materials could provide a similar sound absorption compared to acoustic materials conventionally used in outdoor applications. Afterwards, the investigated materials were used to design and optimise a prototype of a street furniture element with potential implementations in different urban parks. The design and optimisation process was developed by using a simulation based on the Finite Element Method.

1.

Introduction

Noise issues have gained significant importance during the last fifty years because of the fast urbanisation process worldwide. In particular, 30% of the EU population is exposed to noise levels exceeding 55 dB(A) during night time [1]. At a policy level, the aim for a common encounter of the problem led to the adoption of the EU Directive on Environmental Noise [2] for the assessment and management of environmental noise. However, the need to mediate noise assessment with people’s perception and not only with the traditional use of LAeq led to “Soundscape”. Murray Schafer [3] initially introduced the concept of soundscape. He reported that, in the evaluation of an environment, the visual aspect often prevails on the acoustic one. His study investigated the effects of the perceived sounds on humans in the outdoor sound environment. According to Shafer, “Soundscape” can be explained as a mediator between humans, their activity and their environment. Compared to the conventional environmental acoustics approach, focused more on noise reduction, the soundscape approach is characterized by centrality of human perception, since it is defined as “the acoustic environment as perceived or experienced and/or understood by a person or people, in context” [4], giving more emphasis on the acoustics subjective sphere. It is essential to use acoustic and psychoacoustic indicators [5,6], where the attention is focused on the person who lives in a certain soundscape environment.

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The 23rd International Congress on Sound and Vibration

People are often so conscious of sounds that are “negative” that they tend to neglect those that are “positive”. The reduction of noise is often not accompanied by the substitution of more pleasant sounds [7]. An example is represented by the regeneration project of the Valley Gardens in Brighton & Hove [8,9,10], which highlighted how the presence of a street close to a park can damage the soundscape quality of the park and reduce the use of such a crucial place, for the city of Brighton, in terms of social activities and public appreciation [11]. Using the Valley Gardens project as a case study, the present research aimed to design a screen that allows a localised noise control coming from a certain direction, without the exclusion of the desirable sounds coming from the park. This can be considered as one of the most important features influencing the global assessment of parks quality [12]. The screen should not affect the visual perception, by applying on already existing street furniture such as benches. The tool to bring the research from a conceptual stage to a realized stage was identified in 3D printing.

2.

Design

2.1 Material The acoustic properties of three different 3D printing materials were investigated. These included ceramic powder, polylactic acid (PLA) based filaments and acrylonitrile butadiene styrene (ABS) based filament. A first comparison among them was made with the physic data declared by the manufacturers, as shown in Table 1, while a second one was made through the results of normal incidence sound absorption coefficient measurements performed by impedance tube. Table 1: Physic characteristics of the investigated 3D printing materials. PHYSIC CHARACTERISTICS

Appearance

Diameter accuracy mm

Relative density g/cm3

Tensile strength (max.) MPa

Flexural modulus GPa

Impact strength, (Charpy) KJ/m2

PROJECT SUITABILITY

MATERIALS

Ceramic Powder PLA

PLA ABS

zp 150 Powder ColorFabb Signal Yellow Fenner Drives NinjaFlex

Powder

0.3

2.6- 2.7

2.5

12

2

Low

Filament

1.75 ± 0.05

1.3

35

4

12

Good Eco-friendly

Filament

1.75 ± 0.05

1.2

61.5

0.0033

30.8

Good Eco-friendly

XT-WHITE

Filament

1.75 ± 0.02

1.05

48

2.2

20

Good

The second stage of analysis was accomplished just for the two different kinds of PLA, ColorFabb Signal Yellow and Fenner Drives NinjaFlex, due to their eco-friendly component compared to the ABS, which comes from petroleum processing and is non-recyclable. In total three samples were produced to be tested in an impedance tube. Two of the samples were made by the basic PLA, designed as Helmholtz resonators as shown in Figure 1, with 25% and 50% of perforation percentage, whereas another one was produced with 35% of fill density with a simple extrusion of the Fenner Drives NinjaFlex material.

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ICSV23, Athens (Greece), 10-14 July 2016


Figure 1: Pictures of the three samples for the impedance tube test.

The comparison among them proved that PLA NinjaFlex was the most appropriate to continue with because, having a similar sound absorption to simple PLA samples, it has more malleability and an easier printing preparing process. These values were then compared with the coefficients of the most common materials used as acoustic and street furniture devices, such as smooth and coarse concrete, plywood and wood panels. A comparison with an optimal acoustic absorber, such as a 50 mm thick panel of mineral wool with a density of 40 kg/m3 is also reported. The results presented in Figure 2 showed that PLA has a higher absorption coefficient than smooth concrete, plywood and wood and lower than mineral wool and coarse concrete over 250 Hz. Apart from the acoustic properties, its simplicity in the design and printing process render it more appropriate than other conventional materials for an outdoor soundscape study.

Figure 2: Comparison with absorption coefficient of other materials.

2.2 Design concept and optimization At first, a review of the current tools dealing with sound propagation was performed, such as loudspeakers, inside parabolic screens or outside street screens. Nowadays in the market it is possible to find several anti-noise devices as street barriers, but they are visually invasive. For this project, the produced object was built in such a way to be integrated in the landscape and at the same time to reduce traffic noise levels at the receiver’s position. Consequently, the design process was focused on middle dimension models able to be integrated in existing street furniture using the 3D printing technology. After the choice of the design strategy, it was necessary to realize a 3D model through the software Rhinoceros and then to import it in COMSOL Multiphysics, a Finite Element Method (FEM) simulation software. To run the study it was essential to define the boundary conditions for the frequency ICSV23, Athens (Greece), 10-14 July 2016

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domain. Consequently, the source was set as a surface source measuring 25 × 300 cm with a height assumed at 80 cm to simulate an average of the most common engines heights of the vehicles that could cross the street relative to Brighton case study area. The source was set to emit a white noise with a sound power level of 80 dB, applied on one interior surface of the boundary box, measuring 400 × 400 × 220 cm. In order to analyse the sound propagation (250 Hz) at different distances from the source a study line was set with a parallel direction to the y axis and a height of 110 cm. This was assumed as an average value for a sitting adult person with ear height at 140 cm and a sitting child person with ear height at 80 cm. In every phase of the design optimization study the screen was placed 200 cm away from the source in the centre of the box and with a height of 70 cm so to simulate its position over a bench. In order to perform a design optimisation process, it was essential to characterise the 3D model with the PLA NinjaFlex physic-acoustic properties, carried out in the first stage of analysis using the impedance tube. The design process started with a rectangular panel (reference case, Figure 3a) measuring 180 × 100 × 6 cm and, through the study of three more cases, reached to a curve shape model (Case 4, Figure 3b) with a built volume of 60 × 40 × 20 cm and a shape thickness of 3cm.

a

b

Figure 3: Prospective of Reference case (a) and prospective of Case 4 (Final case=b).

Finally, running the study with the boundary conditions and the setting described above, the sound attenuation produced by the volume reduction and the shape modulation of the screen was obtained. For the sake of simplicity, Figure 4 shows only the trends of Sound-Pressure Level (SPL) with source distance for the reference and the final case. The observation was focused mostly on the central part of the screen, where the user’s head is expected to be (10 cm far from the screen and 110 cm off the ground). In particular, Figure 4 shows that for the reference case there is a significant attenuation of the SPL, but this is placed more than 50 cm after the screen. On the contrary, it can be seen that the attenuation for the final case – still to a reasonable extent – is close to the screen at a distance of 10 cm and a medium height for ears at 110 cm. The results demonstrate that the geometry design process has defined a precise area where the SPL attenuation is concentrated.

Figure 4: Correlation between SPL and distance from the source for reference and final case. 4



2.3 The printing and the building of the prototype Following the design optimization process it was necessary to prepare the original 3D model in the physical scale. To keep the design simple, the structure was divided in 59 modular pieces printed across four 3D printers (model Ultimaker2 Extended) at the University of Sheffield laboratories. This occurred by creating a specially designed jigsaw shape in the pieces, which allows connections without the use of glue as presented in Figure 5. The design included a shape adaptable to different kind of benches backrests, as shown in Figure 6.

Figure 5: Built prototype from different viewpoints.

Figure 6: Render of an application of the prototype in a public area.


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3.

Performance

3.1 Laboratory measurement The built prototype was tested in a semi-anechoic chamber of the University of Sheffield in order to measure its acoustic performance in terms of Insertion Loss (IL), which is the difference of SPL between two different sound or geometric configurations, in this case without and with the screen. It was chosen a semi-anechoic chamber because it simulates the real screen context (as in the park the ground is semi-rigid as the one of the chamber). For the test, as shown in Figure 7, it was used a loudspeaker (model: HS7 powered studio monitor Yamaha). Boundary and geometrical conditions were assumed with the loudspeaker placed two meters far from the screen, after which, 10 cm away, was placed a dummy head (model: Neumann KU 100 Binaural Dummy Head Microphone System) to simulate the binaural acoustic capability of an individual. In order to test a variety of combined solutions, the source producing a white signal noise was moved in five different positions relatively to the screen as shown on Figure 8. For each position the head was moved perpendicularly (Relative Head Position=RHP) to the screen at a distance of 10 and 40 cm away (Figure 8). Then horizontally in a parallel direction to the screen (central to the screen and moved 10 cm to right) (Eccentricity=E). In total twenty measurements were carried out and repeated both with and without the screen.

Figure 7: Configuration of the semi-anechoic chamber with the screen.

Figure 8: Scheme of the anechoic chamber configuration (left) and of the head tested positions (up). 6



3.2 Measurement results In total, the calculated IL reached a maximum level of 4.4 dB(A) when the source was at position 1 according to Figure 9. On the other hand, at a distance of 200 cm from the source, the IL drops to 1.5 dB(A) and in the mean distances between 50 cm and 150 cm it varies from 4.3 to 2.8 dB(A). According to Figure 9a it is proved that the closer to 1 source position the higher the IL. Moreover, from the results it is clear that to feel the screen effect the user has to be in the immediate proximity of it as shown in Figure 9b. Figure 10 reports the frequency dependant trend of the value of Insertion Loss obtained by averaging the results of the measurements performed in all the configurations. As expected, the higher the frequency, the higher the SPL attenuation. Definitely the main advantages of the developed screen are: a) the idea of having a screen whose noise reduction is localized on a specific area, and b) the filtering of sounds from specific directions by reducing their effect in middle-high frequencies.

a

b

Figure 9: IL graph depending on the source position (a) and on relative head position (b).

Figure 10: Average IL value vs frequency.


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4.

Conclusions

The findings presented in this study have highlighted interesting results regarding the acoustic suitability of 3D printing materials, the suitability of acoustic design using software simulation and the actual performance of the 3D printed prototype, experimentally assessed in laboratory conditions. Conducting this research had an impact on understanding the design process and the potential benefits of acoustic furniture construction for soundscape purposes. This led to the realization of a relatively cheap and ecologically sustainable prototype that could be assembled in a flexible way. Nowadays, the 3D printing technology is increasingly becoming an integral part of everyday reality. Therefore, the soundscape process, as an interdisciplinary field, can incorporate these new technologies and take advantage of them in terms of study method and of tools to progress this research. If this technology is properly supported it will likely lead to the development of better, more intuitive systems, creative designs, and smarter manufacturing processes.

REFERENCES 1 World Health Organization. [Online.] available: http://www.euro.who.int/en/health-topics/environment-

and-health/noise/data-and-statistics/ 2 European Parliament and Council., Directive 2002/49/EC relating to the assessment and management of

environmental noise. Brussels: Publications Office of the European Union, (2002). 3 Schafer, R. M. The tuning of the world. Knopf, New York, NY (1977). 4 International Organization for Standardization., ISO 12913-1:2014 Acoustics — Soundscape — Part 1:

Definition and conceptual framework. Geneva, Switzerland, (2014). 5 Aletta, F., Kang, J., and Axelsson, Ö. Soundscape descriptors and a conceptual framework for developing

predictive soundscape models. Landscape & Urban Planning, 149, 65-74, (2016). 6 Aletta, F., Kang, J., and Axelsson, Ö. Towards acoustic indicators for soundscape design. Proceedings of

the 7th Forum Acusticum, Krakow, Poland, 7–12 September, (2014). 7 Stockfelt, T., Sound as an existential necessity, Journal of Sound and Vibration, 151, (1991). 8 SONORUS, FP7-People (ITN) Programme. [Online.] available: http://www.fp7sonorus.eu/ 9 Aletta, F., Kang, J. Soundscape approach integrating noise mapping techniques: a case study in Brighton,

UK. Noise Mapping, 2, 1-12, (2015). 10 Easteal, M., Bannister, S., Kang, J., Aletta, F., Lavia, L., and Witchel, H. Urban Sound Planning in

Brighton and Hove. Proceedings of the 7th Forum Acusticum, Krakow, Poland, 7–12 September, (2014). 11 Lavia, L., Witchel H.J., Kang, J., & Aletta, F. A preliminary soundscape management model for added

sound in public spaces to discourage anti-social and support pro-social effects on public behaviour. Proceedings of the DAGA 2016 Conference, Aachen, Germany, 14–17 March, (2016). 12 Brambilla, G., Gallo, V., Asdrubali, F., and D'Alessandro, F. The perceived quality of soundscape in three

urban parks in Rome. Journal of the Acoustical Society of America, 134 (1), 832-839, (2013).

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