SoundCape. Combating Environmental Noise in Urban Areas

Sophie Luger

Sophie Luger (Institute of Architecture) and Lenia Mascha (Institute of Architecture) address the increasingly important issue of urban noise pollution. "SoundCape. Combating Environmental Noise in Urban Areas" explores how sound and noise prevention can be incorporated into architectural design. To develop building structures for noise control in urban environments, the authors examine contradictory historical approaches from architecture and acoustics to learn about the relation of sound and material. Their approach focuses on geometry; experiments with Chladni patterns show that geometrical and material properties of architectural façades have an impact on spatial acoustics and result in the design of ornamental elements that can reduce unwanted noise in cities.

“Noises are the sounds we learned to ignore.”

R. Murray Schafer, The Soundscape:

Our Sonic Environment and the Tuning of the World, 1994

In February 2022, we initiated an architectural research project on acoustic ecology and architectural design. The reasons for doing this were manifold. First and foremost, we felt it was important to address the impact of noise pollution on the welfare of cities, an often-overlooked aspect of city planning and urban design. In particular, urban soundscapes affect the health and well-being of all life coexisting in urban spaces. Rethinking architectural design to create a more sustainable acoustic environment is an approach that goes hand-in-hand with a joint attempt by architects and designers to bring environmental concerns to the foreground of their disciplines today and direct their efforts toward a sustainable and ecologically aware urban future. As architects with a strong focus on design, we saw the potential to employ our own experience in computation, urban strategies, architectural practice, and pedagogy to address architecture’s relevance to the field of environmental acoustics. This research area has been commonly associated within the architectural profession with building physics and product solutions for noise abatement; however, it has not been prioritized in the design decisions of early conceptual phases of planning. Several measurements and planning principles can be employed to redirect sound and shield critical areas from noise, like optimal building position and well-considered floor plans (Jaramillo and Steel, 2015). We decided to focus our attention, however, on a possible performance of architectural facades and the retargeted role of geometry and ornamentation on building skins for noise regulation. Recent studies on urban acoustics show the potential of building envelopes to provide acoustic comfort to outdoor spaces (Crippa et al. 2019; Krimm et al. 2017), thus highlighting the role of buildings in defining the public space both spatially and aurally. In our study, we aimed to extend this premise further through an interdisciplinary design approach that draws its methods from art, science, and technology. We sought to explore a sound-informed design strategy through the study of vibrational phenomena and the ability of sound to produce ornamental figures. The early pathways of our research journey have been formed by ideas on sound behavior and architectural acoustics, together with experiments in digital simulations and physical measurements, which we are going to present in this article. Titled “SoundCape,” the project was initiated with the support of the Angewandte Program for Inter- and Transdisciplinary Projects in Art and Research (INTRA), which is funded by the Austrian Federal Ministry of Education, Science, and Research.

Working on the SoundCape project, we investigated which geometries could inform the design of building elements to reduce noise pollution in urban environments. More specifically, could ornamentation become a highly specialized agent in reducing unwanted noise in cities today? To seek answers, we first had to address a more profound question: What is sound, and how does it relate to material and geometry?

In his 1912 essay “The Mystery of Acoustics,” Viennese architect Adolf Loos asserted an almost supernatural relationship between materials and architectural acoustics (Loos 1995). As a famous adversary of ornament and the non-modern world, Loos rejected the common principles of acoustic solutions related to architectural dimensions of space and instead proclaimed that exceptional acoustics result from architectural materials. He placed his emphasis not on inherent physical properties of matter but on such developed in time after long-term exposure to “good” music. The Viennese architect considered the classical orchestras of the imperial music halls of his time as such music. In his view, the materials’ physical properties could change and improve their acoustic resonance when impregnated long enough with these compositions. For Loos, it was the distinction between soaking matter in “good” or “bad” sounds that resulted in a better or worse aural experience. Similarly, his polemic writings asserted a distinction between a primitive and a modern world that embraced or rejected ornamentation in architecture and design respectively (Loos 2019, p.188). We can assume that this distinction did not merely derive from the architect’s aesthetic dogma but has coincided with the acoustic theory of his time, including the writings on “unmusical sound” by Hermann von Helmholtz and his definition of noise “as sound composed of nonperiodic vibrations compared to music which consists of periodic vibrations” (Schafer 1998, p.182). Even if Loos’ acoustic arguments were not supported by scientific measurements and have probably raised a series of objections in the acoustic engineering community, they did highlight a thought-provoking architectural understanding of space. This understanding surpassed static models of geometric cartesian characteristics as an active field of interactions between sound energy and materials that could transform one-another in time. In other words, “The Mystery of Acoustics” proposed the radical idea that a two-way transformational relationship between sound and matter is possible and affected by sound’s musicality.

The relationship between sound and matter has been continuously studied in acoustic theory. Particle motion through sound vibrations has been physically proven and researched by many protagonists in the field. Most notably, particle motion was studied by the 18th-century scientist and musician Ernst Chladni in his work on vibrating acoustic plates. Chladni’s famous physical experiments relied on a violin bow and a metal plate with dispersed tiny sand particles. Fixing the plate on its center and drawing the bow over its edge in various positions, resulted in the vibration of the metal plate, and, subsequently, in the sand particles’ motion. Chladni’s research would set a fundamental cornerstone for modern acoustics (Zhou et al. 2016) and became a major inspiration for scientists and artists. Two centuries later, Hans Jenny revisited the Chladni patterns and produced an extraordinary body of work that cataloged a series of solid and liquid sonorous patterns and figures sculpted by sound and magnetic fields on different materials (Jenny 2002). Jenny’s experiments and cymatic research anchored their existence on the art-science spectrum. They constituted a major precedent for the studying, simulating, and understanding sound phenomena in an empirical and visual way.

In a rigorous comparative study between Loos’ polemical writings and the Chladni experiments, an interesting discussion arises, bringing the concepts of sound and ornamentation to the fore. Though Loos supported the idea of sound’s ability to penetrate and change the acoustic efficiency of materials and architecture, he undermined the role of geometry and space dimensions. The aphorism of unnecessary decoration and superfluous ornamentation of utilitarian objects (Loos 2019) echoed the general modern view that defined the architecture of the 20th century. However, in the context of spatial acoustics, geometry plays an important role in sound quality. Geometrical characteristics, including typology, proportions, complexity, cavities, and porosity, result in dispersing, enhancing, and absorbing sound energy. Furthermore, decorative patterns on the walls of, for example, Renaissance concert halls, facilitate sound diffusion while they also contribute to eliminating echoes and focalizations (Jaramillo/Steel 2014, p.162-167).

The experiments of Chladni and Jenny reveal a morphological footprint of sound frequencies on vibrating materials that can appear exceptionally intricate and ornamental. When Chladni excited the plates with a violin bow, he generated two-dimensional standing waves that represented the plates’ inherent frequencies.1 Standing wave nodes appear as individual points in one dimension, while they materialize as lines in two dimensions. Therefore, the patterns are not exactly visualizations of sound. They constitute sound-driven formations because the sand particles oscillate with the changing sound frequency. They get moved away from the sound wave’s antinodes to accumulate and settle on the nodal lines emerging on the metal plate (Coughlin 2000, p.133). Chladni patterns also depend very much on the material of the plate, whose geometrical (size, shape, thickness) and physical properties (material density) significantly influence the patterns of the generated sand particles. When the applied sound frequency corresponds to its few dominant eigenmodes, the patterns are well-defined and clear to see. The sand patterns appear more chaotic when the applied sound consists of a wider range of frequencies, and the interference of multiple modes leads to a less defined outcome. Therefore, different sound frequencies result in different formations, and pure-tone sound events (single frequencies) generate clearer figures when they correspond to the particular eigenmode of the plate.

To study the Chladni patterns empirically, we conducted physical experiments using sand particles on a centrally fixed 12” carbon fiber plate, with an integrated loudspeaker at its center, connected to a computer source. Running the experiment with different sound inputs, we observed that the voice of an opera singer penetrating the metal sheet through the loudspeaker behind it could also result in similarly clear sound patterns. In contrast, noisy or very loud sounds would spread the particles all over the plate, most of the time. We could thus reflect on Loos’ “good” music and Helmholtz’s “musical sound”, bringing aesthetics, artistic expression, and physics in close dialogue. Both Loos’ arguments on the mystery of acoustics and the research by Chladni/Jenny reveal an inspiring point of departure. Together, they highlight how sound penetrates physical bodies, oscillates our cells, and evokes movement, going beyond an emotional or a psychological response.

Today, we could argue that the architectural surfaces of modern cities are impregnated with all sounds but silence. When M. Schafer (2012) provided his definition of the city soundscape, he extensively addressed the impact of technological sounds and their contribution to noise emissions in the urban sphere. This urban cacophony, often understood as an inseparable part of the city’s livelihood and lifestyle, bounces back from the walls, streets, and physical objects it impacts. It penetrates our bodies and significantly influences the well-being and health of millions of people and ecosystems (World Health Organization 2010; European Environmental Agency 2020).

In SoundCape, we acknowledge that architectural facades’ geometrical and material properties impact spatial acoustics and environmental noise regulation. Hence, there is a strong potential for architectural design to improve the environmental acoustics of cities. Since Adolf Loos’ time, the role of ornament in architecture has changed profoundly. Advances in digital technologies have been constantly retooling the architectural discipline, providing many possibilities for design, composition, simulations, and the intelligent performance of complex geometries. Computation has further enabled a new understanding of spatial acoustics. Sound can now become visible, and it can be rendered and simulated to reveal new ways of acoustic optimization. Innovations in architectural materials, together with digital design and production techniques, can also help in developing new acoustic solutions for architecture.

SoundCape examined the effect of different facade geometries on noise levels in densely populated urban areas, using a simplified model of two buildings with various architectural skins that were facing each other. The materials applied to the building fronts were mostly sound-reflective, such as metal or glass, and plaster as another commonly used facade material. We employed the open-source acoustic simulation platform, “Pachyderm Acoustical Simulation” to visualize sound dispersion and reverberation time changes for comparison. The platform is embedded in the parametric design environment of Grasshopper, a plugin for the 3D modeling tool Rhinoceros. The resulting simulation shows that various facade elements might potentially affect sound levels through the build-up within the street canyon. Additionally, the animations visualized the possibility of focalization effects and sound dispersion through the proportions and different geometries of the abstracted facades.

Alongside acoustic models on an urban scale, our research also ran a parallel course that was driven by the Chladni sonorous figures. This parallel investigation did not start from a given premise where vibrational phenomena are connected with environmental acoustics. Noise emissions in the open field have nothing to do with particles’ movement on the metal plate. Yet, the sound’s visual footprint on the shaken sand gave us the first clues for our geometrical investigation. Our literature research, and in particular, the experiments of Chladni and Jenny, have pointed out the visual traces of physical sound phenomena that remain invisible most of the time and are thus difficult to grasp. In that way, we acknowledged their potential to pave the ground for architectural acoustics to benefit from. What further motivated us to investigate their acoustic characteristics has been related to their basic organizational and geometrical principles. We intuitively discussed formal associations to Helmholtz Resonators or Schröder Diffusors, which are commonly applied to enhance room acoustics in various ways. Specifically, Helmholtz resonators are used to absorb selected frequencies through the proportional relationship between their opening, neck, and volume (Jaramillo/Steel, p. 219-229). Searching for traces of similar geometrical attributes with sound absorption capabilities led us to explore vibrational patterns more deeply. Vibrational phenomena can be described by mathematical equations. By translating them as lines of code in our modeling software, we generated a three-dimensional digital model that we were able to control and manipulate by feeding different values to the multiple parameters of the function. In order to develop the same experiments in three-dimensional space beyond the two-dimensional plane, we followed the research paper titled “Chladni Figures Revisited – A Peek Into the Third Dimension” by Martin Skrodszki, Ulrich Reitebuch and Konrad Polthier (2016). The paper provided us with the mathematical formulas that described the Chladni patterns in three dimensions. Once we parametrized our digital models, we could produce infinite results of these sonorous forms. Could we translate these sonorous figures following their inherited organizational grid lines and continuously evershifting wavy nodes to an acoustic facade design?

Similar to the physical experiments of vibrating sand patterns, not all the resulting models appear equally clear, appealing, or share the same acoustic potential. For this reason, we selected three of the numberless possible results, which provoked our interest and intuition regarding acoustic performance. Their unique complexity and natural intricacy have motivated us to further test them in the context of the research question: Could their entangled continuous surfaces and cavities capture sound energy and thus work as sound absorbers? Material and scale were expected to influence the result significantly. Therefore, we paused our design research and shifted the focus to digital fabrication. The three exemplary forms were 3D printed in quartz sand, a material that can achieve extreme precision in fabricating complex geometrical forms. It has a rough, porous texture and is water-resistant, qualities that are very important for weather protection in the outdoors. For this reason, we excluded other effective sound-absorbing materials like soft and spongy matter or foam and felt, as harsh weather conditions, safety aspects, and wildlife must be considered in the free field.

In order to test the acoustic characteristics of the selected quartz sand objects, which were 20x20x20 cm in size, we performed acoustic-physical measurements. The tests were conducted with the support of the engineering office “Akustik-Design Austria.” The chosen research methodology included an acoustic camera (CAE SoundCam 1.0.) and a small loudspeaker emitting pink noise, followed by a detailed analysis and presentation of the findings. The measurement conditions and equipment used during the study were meticulously documented, including the study period and spatial conditions. The impact of perpendicular incident sound waves and waves at an angle to the object were measured to investigate the three distinct elements’ shape-specific sound transmission and sound reflection characteristics. Furthermore, it was tested how the measurement would change if objects were filled with fibrous material, such as sheep wool. Examining sound transmission measurements involved positioning the element between a loudspeaker and the acoustic camera, irradiating it with pink noise, and recording sound pressure levels and frequency spectra. The results indicate the varying degrees of sound pressure reduction introduced by the examined elements and were presented in a spectrogram format, providing visual representations of frequency characteristics and sound pressure levels, with color coding indicating sound levels. The study revealed differences in how the three blocks transmit sound, leading to element-specific spectral changes.

Investigating sound reflections at different points on the elements and their response to pink noise turned out to be more revealing. The image shows that introducing the examined object into the sound propagation path results in varying sound reflection reduction for each object.

While all elements showed some absorptive characteristics, one element, in particular, showed unexpectedly high-level differences to the incoming sound, measuring 7,3 dB. Although the described setup does not replace a standard-compliant measurement of the sound absorption coefficient in a reverberation room, it provides interesting clues regarding which geometrical properties we should investigate further. The results provided a good basis for analyzing the 3D printed objects and ideas on which areas to further focus on when developing the objects’ geometry.

The first stages of our research focused on generating and gaining control over the synthesis of sound-informed ornamental structures and their acoustic evaluation. The jump to the urban scale has been hypothesized and supported by our comparative studies of the acoustic simulation on city fronts. The open-source simulation tools have proven to be useful in further investigating simplified models of building facades and their capacity to disperse, focus, and redirect sound. Yet due to the increased level of detail of the generated forms, the physical measurements proved to be a valuable addition for acoustic evaluation. Projecting the next steps, the research outcomes should be further evaluated in order to gain a better understanding of the three-dimensional patterns in different scales and combinations, ultimately leading to an optimized design for achieving the most optimal noise-regulating capability. For contributing to a more viable proposal, these forms would also need to take into consideration the appropriate scale of intervention, the contextual conditions including the location of the noise sources, the type of noise, and the appropriate materials in addition to safety and environmental factors. Defining the next steps of the research, we aim to design a facade panel prototype, in scale 1:1, with concrete considerations on its materiality, structural assembly, and durability. This panel could be further tested in a reverberation room and during different timeframes in the open field, where natural parameters, weather conditions, and the natural decay of building materials and their conservation could be addressed. Of course, the complexity and multifactorial nature of environmental noise call for multiple responses and many action steps to achieve a healthy and qualitative city soundscape. Architectural practice can strengthen one part of this response, yet a synergy between urban planning, architectural design, and building physics is required in order to provide sound-regulating solutions for public spaces.

SoundCape is a research project by Sophie Luger and Lenia Mascha which was conducted between 2022–2023 at the Institute of Architecture and with the support of the Center Research Focus at the University of Applied Arts in Vienna. This research project was funded in whole by the INTRA program of the University of Applied Arts Vienna.

The digital simulations of the Chladni experiments have been conducted using the 3D animation software SideFx Houdini.

The acoustic simulations have relied on the Acoustic Simulation Software Pachyderm within the environment of the software Rhinoceros 3D.

The acoustic measurements of the quartz-sand elements were conducted at Akustik-Design Austria with Dr. Harald Graf-Müller and Valentina Graf, BSc., www.akustikdesign.at.

Tommaso Crippa/Edoardo Dagnini/Gareth Davies/Harry Rees, “Façade Engineering and Soundscape”, 2019, URL: www.burohappold.com, accessed on October 20 2023.

A.M. Coughlin, 2000, “Patterns in the Sand: A Mathematical Exploration of Chladni Patterns”, The Journal of Mathematics and Science: Collaborative Explorations Volume 3: No 1, Article 20, pp. 131-146. DOI: https://doi.org/10.25891/YZDP-NS05

European Environment Agency, Environmental Noise in Europe, Publications Office, 2020, URL: https://data.europa.eu/doi/10.2800/686249, accessed on April 30 2023.

Ana M. Jaramillo/Chris Steel, Architectural Acoustics, Routledge, 2014. DOI: https://doi.org/10.4324/9781315752846

Hans Jenny, Cymatics. A Study of Wave Phenomena and Vibration. A Complete Compilation of the Original Two Volumes by Hans Jenny, Oxford: Oxford University Press 2007.

Jochen Krimm/Holger Technen/Ulrich Knaack, 2017, “Updated urban facade design for quieter outdoor spaces”, Journal of Facade Design and Engineering, [online] 5(1), pp. 63–75. DOI: https://doi.org/10.7480/jfde.2017.1.1422

Sophie Luger/Lenia Mascha, SoundCape online project documentation. URL: https://soundcape.uni-ak.ac.at/, accessed on October 20 2023.

Adolf Loos, “Das Mysterium der Akustik (1912)”, in: Adolf Loos, Über Architektur – Ausgewählte Schriften. Die Originaltexte, Adolf Opel (ed.), Wien: Prachner 1995.

URL: https://www.nextroom.at/data/media/med_binary/original/1212475132.pdf, accessed on April 30 2023.

Adolf Loos, “Ornament and Crime (1908)”, in: Adolf Loos, Ornament and Crime: Thoughts on Design and Materials, transl. by Shaun Whiteside, London UK: Penguin Books 2019.

Michael Möser, Technische Akustik, Springer: Berlin Heidelberg 2007.

R. Murray Schafer, The Book of Noise, Indian Ridge Ont: Arcana Editions 1998.

R. Murray Schafer, The Soundscape. Our Sonic Environment and the Tuning of the World, Vermont: Destiny Books 2012.

Martin Skrodzki/Ulrich Reitebuch/Konrad Polthier, “Chladni Figures Revisited:

A Peek Into The Third Dimension”, Bridges Finland Conference Proceedings 2016: Mathematics, Music, Art, Architecture, Education, Culture.

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URL: https://www.who.int/europe/news-room/fact-sheets/item/noise, accessed on April 30 2023.

Quan Zhou/Veikko Sariola/Kourosh Latifi/Ville Liimatainen, “Controlling the motion of multiple objects on a Chladni plate,” Nature Communication 7, 12764/2016. DOI: https://doi.org/10.1038/ncomms12764

Fig. nr. 1: Physical experiments using a Chladni plate in connection with digitally simulated diagrams of the plate’s vibration modes © Simos Batzakis 2022

Fig. nr. 2: Video documentation of the physical experiments using a Chladni plate and sectional diagrams of the plate’s vibration digitally simulated © Sophie Luger and Lenia Mascha 2022

Fig. nr. 3: Acoustical simulation of abstracted facade geometries visualizing various focalization effects and sound dispersion within the street canyon using “Pachyderm Acoustical Simulation” © Sophie Luger and Lenia Mascha

Fig. nr. 4: Video showcasing the acoustical simulation of abstracted facade geometries visualizing various focalization effects and sound dispersion within the street canyon using “Pachyderm Acoustical Simulation” © Sophie Luger and Lenia Mascha 2022

Fig. nr. 5: Video still showing the digital simulation of Chladni figures, generated with the mathematical equations describing their vibrational movement. © Sophie Luger and Lenia Mascha 2022

Fig. nr. 6: Digital simulation of Chladni figures, generated with the mathematical equations describing their vibrational movement. © Sophie Luger and Lenia Mascha 2022

Fig. nr. 7: Video still showing the digital simulation visualizing the Chladni figures, generated with the mathematical equations that describe their vibrational movement in the third dimension. © Sophie Luger and Lenia Mascha 2022

Fig. nr. 8: Digital simulation of the Chladni figures, generated with the mathematical equations that describe their vibrational movement in the third dimension. © Sophie Luger and Lenia Mascha 2022

Fig. nr. 12: Sound Transmission Measurement: Three distinct quartz-sand objects were examined, each possessing unique surface characteristics and cavity structures. The measurement results were summarized in a spectrogram format, visually representing the frequency characteristics and sound pressure levels. © Akustik-Design Österreich, Dr. Harald Graf-Müller, www.akustikdesign.at

Fig. nr. 13: Introducing the examined elements into the sound propagation path caused different reductions in sound reflections. © Akustik-Design Österreich, Dr. Harald Graf-Müller, www.akustikdesign.at

Fig. nr. 14: Perpendicular Sound Incidence – Reflections on Element 2, Level Difference: 5.4 dB © Akustik-Design Österreich, Dr. Harald Graf-Müller, www.akustikdesign.at

Fig. nr. 15: Perpendicular Sound Incidence – Reflections on Element 3, Level Difference: 7 dB © Akustik-Design Österreich, Dr. Harald Graf-Müller, www.akustikdesign.at

reposition ISSN: 2960-4354 (Print) 2960-4362 (Online), ISBN: 978-3-9505090-8-3, doi.org/10.22501/repos

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Sophie Luger, Lenia Mascha - SoundCape. Combating Environmental Noise in Urban Areas - 2024