This research does not presume that architectural and urban design never use sound, as ample research and design precedents apply the science of acoustics. Rather, design methods that address sound as a primary parameter are employed in specialised buildings such as assembly spaces (concert halls, sound studios, or lecture halls), not as the norm for general spaces.
In reference to neurobiological research, successful acoustical techniques consider the physiological effect of sound. Classic Greeks successfully built the Epidaurus Amphitheatre in the fourth century B.C.; yet, through multiple attempts, they were still unable to reproduce the methods that generate the unique acoustic qualities of the amphitheatre. Recent ultrasonic investigations reveal the significant property that distinguishes this space. Discussion is included on the aurally honed perception techniques that the ancient Mayan civilization used to construct a temple using complex geometry and material morphology to convey a particular narrative.
Concert halls are a well-established typology of buildings developed continually since the classical Greek amphitheatres. This post reviews the Segerstrom Performance Hall, designed by Charles Lawrence in 1983, and the McDermott Concert Hall, designed by I. M. Pei in 1989. These halls fuse acoustical strategies that are still applied and revised. The issues discussed here have significant implications on space and influence fundamental architectural characteristics. Among these features is room volume, ceiling height, longitudinal and cross-sectional spans and surface materials (SIEBEIN, Gary W and Kinzey Jr, Bertram Y, 1999).
In conclusion, there are design projects by two modern composers, architects and engineers, Iannis Xenakis and Bill Fontana. The significance of this discussion is the generational gap and opposing design approaches of these two designers. Xenakis designed buildings to compose a series of specific sonic events. In contrast, Fontana harnesses the sonic events that originate from the environment (or building). For both designers’ works, the primary objective is to broadcast a distinct narrative through multi-disciplinary research and methods, such as bridging architecture with art, mathematics, and music. These designers illustrate a firm understanding of how the aural design of a building affects users, and they use that knowledge to their benefit.
Historical Aural Design
Historically, buildings that successfully employ acoustic manipulation techniques incorporate material and geometrical design components. Most acoustic design literature refers to the Mayan Chechen Itza temple and the ancient Greek Epidaurus Amphitheatre. Chechen Itza and its acoustic anomalies speak to the ancient Mayan’s political, religious and cultural objectives. The temple builders lived in the Cloud Forests where auditory stimuli were the primary signals for understanding their surroundings. In the forest, a person can hear objects beyond his or her visual horizon (LUBMAN, David, 1998).
Likewise, the Epidaurus illustrates the ancient Greeks’ scientific and technological advancements. These historic buildings are good examples of filtering certain frequencies via material use and geometrical manipulations to create narratives. The well-preserved Hellenistic theatre of Epidaurus on the Peloponnese in Greece is famed for its acoustical character. Performance sounds issuing from the centre of the theatre reach the outer seats with minimal intensity loss (DECLERCQA, Nico F and Dekeyser, Cindy S A, 2007). The ancient Greeks’ endeavours to replicate the features of this space were not successful, and much dispute exists concerning the primary factors of seating slope, direction of the prominent wind, geometric surface details, and the limestone materials used (MCRAINEY, Megan, 2009). Researchers recently found the geometric and material formula that filters and amplifies low-speech frequencies, simultaneously (SHANKLAND, Robert S, 1973).
Declercq and Dekeyser (2007) conducted a non-invasive ultrasonic wave test on the amphitheatre. The findings reveal that the back seats (the cavea) backscatter the sound to the audience, which creates unimpeded indirect sound waves. The audience receives these indirect waves in a moderately short time after the direct waves originate from the stage (DECLERCQA, Nico F and Dekeyser, Cindy S A, 2007). The simultaneous reception of the direct and indirect waves reflecting off a hard material nearly fuses both sound waves into one amplified sound (LOKKI, Tapio et al., 2011). This event produces loud and high speech intelligibility (AALTO UNIVERSITY SCHOOL OF SCIENCE, DEPARTMENT OF MEDIA
Declercq and Dekeyser’s (2007) ultrasonic tests and numeric simulations infer that the corrugated limestone steps serve as modern-day rigid acoustic padding. The seats function as a high-pass filter to amplify high frequencies and cross over low frequencies (AALTO UNIVERSITY SCHOOL OF SCIENCE, DEPARTMENT OF MEDIA TECHNOLOGY, 2013). This phenomenon varies slightly depending on the periodicity of the seat rows (DECLERCQA, Nico F and Dekeyser, Cindy S A, 2007). The limestone reflects frequencies above 500 Hz and retains those lower than this threshold, which dissipates the audience’s minute coughs and whispers, while the filtering material absorbs the low- frequency waves propagating from the stage. Despite these variances in sound, through cognitive auditory grouping, the audience perceives the performance as a continuous, uninterrupted event (i.e., virtual pitch phenomenon) (ANITEI, Stefan, 2007).
Vowels carry the strongest power of harmonic signals and are the most informative parts of a syllable. All vowels range between 300 and 3000 Hz, which is mostly above the amplification frequency threshold in Epidaurus. If a performer broadcasts from the stage, the backscattering and early reflections amplify the enunciated vowels (AALTO UNIVERSITY SCHOOL OF SCIENCE, DEPARTMENT OF MEDIA TECHNOLOGY, 2013). Through experience or integral visual signals, the brain perceives the delivered speech as uninterrupted legible words (LEVITIN, Daniel J, 2007).
The literature confirms that, like the Greeks, the ancient Mayan civilization in Central America possessed a firm grasp of mathematics, astronomy and social organisation. Unlike the ancient Greeks, the Mayans did not leave written evidence notating their deliberate recognition of acoustical attributes of the structures they built. It has been conjectured that these acoustical attributes are the result of their physical environment and the learnt auditory associations they gained by living in it (BLESSER, Barry and Salter, Linda-Ruth, 2006).
Among these seemingly acoustically designed buildings is the Pyramid of Kukulkan at Chichen Itza, in Mexico. Observers seated on the lowest steps of the pyramid report hearing the sound of raindrops as other people climb the stairs (DECLERCQ, Nico F and Degrieck, Joris, 2004). Acoustic consultant and scientist, David Lubman, discovered that when illuminated by the sound of clapping hands, the staircase of the pyramid produces chirp-like echoes. He dubs this phenomenon as ‘flutter echoes’ (LUBMAN, David, 2006). The resulting flutter echo resembles the sound of the Mayan’s sacred bird and the temple deity, the resplendent Quetzal (BLESSER, Barry and Salter, Linda-Ruth, 2006).
The presence of long stairs that face open courts in other Mayan sites implies that this design feature was purposeful. In traditional western architecture, flutter echoes are considered defects, yet, the Mayans utilised this design to convey a significantly perceptual cognitive narrative. The average flutter frequency in the Mayan Great Ball Courts is 4 Hz, which corresponds to the maximum human sensitivity for auditory warning signals, namely “fluctuation strength.” Reportedly, these echoes resemble the growl of a jaguar or the rattle of a rattlesnake  (LUBMAN, David, 2006).
The Segerstrom Performance Hall and McDermott Concert Hall were built at the time computational simulation was established. Concert halls are interior spaces intended for absolute acoustical purposes, and they employ technical methods that do not provide room for subjective interpretation. Continuous unobstructed sight-lines are a firm non-negotiable parameter that determines spatial geometry. The prime design purpose for such spaces is to configure architectural features to provide high-quality acoustics. These spaces are multi-purpose halls where a range of performance types are conducted (drama, opera, ballet and orchestra concerts), and each hall applies different strategies of acoustic principles (SIEBEIN, Gary W and Kinzey Jr, Bertram Y, 1999).
The Segerstrom Performing Hall, designed by Charles Lawrence in 1983, is a multi-purpose room with a volume of 27,800 m3 that seats 3000 persons. The difficulty here is that the space is required to achieve a level of acoustic quality comparable to a smaller rectangular-shaped room within a much larger space. The occupancy capacity defines the shape of the room—fan-shaped plan—that accommodates the required capacity and sustains uninterrupted sight-lines. This design is based on lateral reflections, which support indirect sound waves that reflect and arrive at the listener’s ears from the side rather than from the back (SIEBEIN, Gary W and Kinzey Jr, Bertram Y, 1999).
Lateral reflections manipulate the aural perception of proximity to create enveloping, intimate and spacious sensations (LEVITIN, Daniel J, 2007). Research on spatial impression indicates that excessively strong lateral reflections may cause confusion and image shift, and the audience may respond to the indirect sound involuntarily. Thus, the lateral reflection technique is ineffective in large spaces. To compensate, designers subdivide the space and vertically stagger smaller spaces to create supplementary sidewalls that provide lateral reflections. This configuration maintains a sense of intimacy and provides adequate sight-lines (SIEBEIN, Gary W and Kinzey Jr, Bertram Y, 1999).
Reflecting and defusing ceiling panels hover over the space close to the audience to provide shorter sound reflections and enhance clarity and loudness. These panels are focused toward the centre portion of the subspaces to guarantee lateral reflection coverage. Gaps between the panels allow some sound energy to travel above them to yield longer reverberation times (2.3 seconds) and create a juxtaposition of short lateral reflections. This combination creates balance between clarity and reverberation—the ultimate goal of any assembly hall configuration. Adjustable curtains positioned in the space between the ceiling and suspended panels may be lowered or elevated to control reverberation for different types of performances (SIEBEIN, Gary W and Kinzey Jr, Bertram Y, 1999).
The McDermott Concert Hall was designed and completed in 1989 by I. M. Pei and Partners, Inc. in coordination with the acoustical consultancy office, Artec Consultants, Inc. Its occupant capacity is 2065 persons and its total volume is 27,800 m2. Principal acoustic consultant, Russell Johnson, was well known for using computational modelling and acoustic simulation in his design study—a novelty at the time. Many historical precedents, including seventeenth-century European opera houses, influenced the design of the McDermott Concert Hall. Among these borrowed historic features is the stacking of several narrow balconies along the edges of the space that adopt a narrow shoebox form and use heavy highly reflective materials on non-uniform surfaces [Refer to: Figure 2. 20]. The use of dense material finishes eliminates the loss of low-frequency reflections.
The space design also incorporates modern architectural and acoustical features, some of which were developed specifically for this space. For example, ‘reverberation chambers,’ large areas surrounding the upper portion of the room, are encased in concrete walls. These areas are segregated from the main hall by operable panels that can be opened and adjusted to assert the amount of reverberation needed for each type of performance. The adjustability of reverberation and its time enables the operator to maintain clarity, which is achieved by balancing the rebounding indirect sound waves with the warm tail of the reverberation effect (SIEBEIN, Gary W and Kinzey Jr, Bertram Y, 1999).
Similar to the Segerstrom Performing Hall, a system of multi-layered screens can be withdrawn into storage spaces along the side walls. These screens are used to minimise reverberation when speech is the primary activity. The design uses a feature that helps propagate low-frequency sounds from the stage toward the audience. A segmented five-layer laminated wood canopy hangs above the stage and is motor-operated to change the angle of inclination. The canopy and reverberation chambers complement each other. If the canopy is raised, low-frequency waves bounce into the reverberation room to enhance sound fidelity. The short reflection time of the canopy increases orchestra members’ abilities to hear each other in time and to gain an accurate sense of their own instruments’ sounds (SIEBEIN, Gary W and Kinzey Jr, Bertram Y, 1999).
Iannis Xenakis, a prominent modern architect, addressed sound and space. As a musician, mathematician, and architect, he formalised his knowledge to manipulate the acoustic perception of his composed spaces (XENAKIS, Iannis, 1997). Xenakis employed multiple parameters to accomplish sonic filtration. Two of these parameters are well-known aspects of the previously cited examples, material and geometry (MATOSSIAN, Nouritza, 2005). Xenakis predated the digital and parametric design boom. His mathematical training enabled him to apply computational and algorithmic principles to filter sound into his architectural practice. This process adopts datasets based on physics, environmental trajectories and material use.
The Philips Pavilion is one of Xenakis’ recognised projects, and was designed while working for Le Corbusier in 1956. The pavilion design intended to highlight the technology that Philips (the company) had to offer. Xenakis’ diverse talents enabled him to develop various features of this project. He wrote the focal sonic event of the project, ‘Poème Électronique’, an eight-minute interlude that synthesises sound and light using Philips’ technology. His research aimed to spatialise the pavilion aurally and was the foundation for developing his consequential polytope investigation.
Hyperbolic Paraboloid forms became Xenakis’ specialty. He developed this geometrical technique during this project to eliminate sonic dead spots, or acoustic shadows.’ Through trial-and-error, he succeeded in pushing the use of concrete to its limits and created a pioneering attempt of free-form geometry. Xenakis’ hyperbolic paraboloid investigations were unconventional at the time. For example, he converted the glissandi structure in ‘Poème Électronique’ into two-dimensional vectors mapped out in time. Without the aid of high-computing machines, the exercise facilitated the adaptation of geometrical and vector calculations to structural vectors to create the complex hyperbolic paraboloid geometry (XENAKIS, Iannis, 1997).
Among Xenakis’ prominent aural designs, Couvent de St. Maria la Tourette and Cité de la Musique employ innovative aural design features. Couvent de St. Maria la Tourette was Xenakis’ first project after holding the position of project architect with Le Corbusier. Xenakis invented his renowned ‘undulating glass panes’ architectural feature for this project for the west façade based on his earlier study The Modular. The Modular is a complex proportional scale formulated to merge human dimension scale with the Golden Mean and the Fibonacci sequence. This process formed his musical solution; double frieze windows of varying widths that create shifting rhythms (LOVELACE, Carey, 2010). When high-speed winds pass over the panes, they generate a harmonic ambient tune (MATOSSIAN, Nouritza, 2005). Xenakis developed related concepts concurrently in his musical piece Metastaseis (1953 1954), which formalises polyrhythms based on superposed stochastic calculations. Almost every design Le Corbusier’s studio produced after 1955 incorporates this feature (XENAKIS,
Cité de la Musique, in Paris, is a natural evolution of Xenakis’ work in which all of his musical, architectural and engineering research culminates. This piece was his entry for a competition held in 1984. While the piece was not selected to be built, it is crucial to consider it along with his scrupulous design thought process of the auditorium ‘Jewel Box of Sound’ (MATOSSIAN, Nouritza, 2005). The design premise considers the auditorium itself as a musical instrument. The generated form became an ellipse-shaped space covered with an inverted tulip-shaped hyperbolic reinforced concrete roof. He also incorporated his other aural design techniques and research, including undulant glass panes (XENAKIS, Iannis, 1997).
Among Bill Fontana’s recently published work, ‘Sonic Shadow’ incorporates ambient live sounds generated by a building. The work is a sound installation at the San Francisco Museum of Modern Art (SFMOMA) that collects sounds caused by forces exerted in a skylight structure and the pedestrian bridge located in the atrium. The design transmutes these architectural and structural elements into musical instruments. The skylight radiates ecological and urban sounds, whereas the bridge resonates with the visitors’ steps. Fontana’s work is primarily technical; he does not modify the structure, he only enables visitors to hear it by capturing the vibrations of the building using a network of high-calibre accelerometers and projecting the signals using ultrasonic carrier speakers that possess a directional throw capacity to target different walls. The projected waves then reflect back to the visitors’ ears. Targeting the sound subdivides the atrium space into distinct aural subspaces visitors can hear different sonic events at different locations (DUFF, Simon, 2011).
Modern composers, such as Xenakis and Fontana, use techniques that consider location as an animated design element and a variable parameter. The deliberate sequencing spatial attributes, together with sonic properties, generate a reciprocal trajectory of sound or space. This transient property defines spaces as a musical dimension. The contiguous composition ‘Poème Électronique’ and the design of the Phillips Pavilion became prototypes of spatial art. The interior space and the visual and aural compositions are superimposed entirely to produce a whole design that is stronger than the sum of its parts. Fontana’s work fuses soundscape music and acoustic ecology within a space to become a living system with natural sounds and acoustics. The use of various speakers increases the spatial design potentialities and presents them as ‘aural architects’ (BLESSER, Barry and Salter, Linda-Ruth, 2006).
 Rattlesnake rattles are usually higher in frequency (LUBMAN, David, 2006)
 Poème électronique “Electronic Poem” is a piece of electronic music by composer Edgard Varèse, written for the Philips Pavilion at the 1958 Brussels World’s Fair (Poème électronique).
 In elementary geometry, a polytope is a geometric object with flat sides, which exists in any general number of dimensions. A polygon is a polytope in two dimensions and a polyhedron in three dimensions