Open access peer-reviewed chapter
Recommended vs. actual reverberation times in public spaces.
Abstract
Currently, acoustic response to curved large-scaled buildings all over the world, such as auditorium, ancient timber temple hall, is changing in a rapidly increasing speed, including technologies’ application (AI, BIM, and simulation technology), new materials, and spacial requirements different than before. Several results indicate that apparent varieties a listener could perceive occur in the audience area particularly with distinctive acoustical configuration, forms. These are interesting possibilities for IAEQ’s performance levels’ up, application and revealing new trend for acoustic environment research (hot focuses and concerns on how IEQ affecting building occupants’ productivity and well-being in a long run). For this particular space type, this chapter explains four aspects, meanwhile, some findings are given out. 1. The key acoustic challenges are the main acoustic phenomenon.
Keywords
- acoustic simulation
- active noise control
- sound-absorbing materials
- current IEQ acoustic regulations
- large curved spaces
1. Introduction
Large curved spaces in public architecture (e.g., exhibition halls, auditoriums, museums, and transportation hubs) present unique acoustic challenges due to their complex geometries, for example, long reverberation times, and sound focusing effects. Curved geometries, such as spheres, cylinders, and cones, even irregular curvilinear form architecture (curved surfaces, freeform structures), refer to ISO 354 standards (measurement of sound absorption in a reverberation room) and ASTM E90 (sound transmission loss), which apply to sound reflection & diffusion. Together with building codes (IBC, EN 12354) for structural stability of curved façades and domes, as well as FAA and EASA noise requirements for aircraft curved fuselages. Besides, there is cladding and paneling, which must account for thermal expansion on curved surfaces. ISO 10140 (laboratory measurement of sound insulation) and DIN 4109 (sound insulation in buildings) guarantee some acoustic materials with proper stiffness and damping to avoid vibration-induced noise. ISO 3382 (acoustic parameters for rooms) and ANSI S12.60 (classroom acoustics) are two classic standards regarding reverberation control in curved spaces. Industrial and environmental noise regulations require that the curved barriers or enclosures must comply with OSHA, EU Directive 2003/10/EC, or ISO 9613 (outdoor sound propagation).
Above mentioned draw forth the chapter’s objectives, that is, providing several best practices for compliance and sustaining interior environment quality (IEQ) at a high level: 1. Simulation and testing: Use acoustic modeling (e.g., FEM, BEM, or ray-tracing software) to predict sound behavior. 2. Absorptive/diffusive treatments: Apply porous materials (foam, fiberglass) or diffusers (QRD, skyline) to curved surfaces. 3. Structural damping: Use constrained layer damping (CLD) for curved metal panels to reduce vibration. In such types of spaces, it requires compliance with acoustic regulations while leveraging advanced technological solutions. This chapter includes four sections that follow and explain the acoustic physics, regulations, problems often occurring, innovative acoustic technologies, and design strategies (metamaterials, active noise control, AI modeling), from the perspective of improving the sound IEQ.
Key acoustic challenges in large curved spaces
Acoustic physics unique to curved geometries
Current 3 acoustic regulations, standards, and compliance strategies on IEQ
Emerging cutting-edge acoustic technologies and design strategies.
2. Methodology
The research methodology in this chapter includes theory analysis, some cutting-edge technologies introduction, and examples of the cases assisted with these technologies. The acoustic technologies summarized in this chapter utilize AI. Moreover, a case study in detail can be acquired in the supplementary appendix, with the acoustic computation simulation method (RAYNOISE software), which is suitable for the big span roof buildings, and more advanced than the ray-tracing method that has been used at present [1]. To calculate the acoustic parameters in this case study, such as clarity, rapid transmission index, or intensity values, we replace diffusing sound waves with sound particles that travel at the speed of sound in the direction of the sound waves. In this process, relatively accurate echogram predictions can be formed after direct sound arrival, and the reflection of the remaining uncertain sound energy density can be screened out with this method, which can achieve the desired prediction effect. How to obtain satisfactory acoustic effects will be underlined considered through taking specific measures to ensure the desired acoustical effects are fulfilled. After the design, appropriate RT, STI, D50, and sound field distribution can be acquired to eliminate the acoustic defects such as echo, trembling echo, acoustic focus, and resonance. One new acoustic material (microporous sandstone sound absorption panel) was also applied for acoustic treatment on the roofs (one was the stadium’s Glass Skylight Vertical Edge) in these three cases, peers can obtain valuable outcomes if they use this methodology in other large-scale space projects. Although a quite number of outcomes about virtual reconstruction of the historical acoustics (such as the ancient Roman theaters and so on) have revealed that they recommend the present general simulation technology, as well as they provide a meaningful reminder of significance for modern acoustics in large-span roof spaces.
3. Acoustic challenges in large curved spaces
3.1 Sound reflection and focusing
Geometric sound distortions [2] are explained primarily below.
Curved surfaces (concave/convex) can cause sound waves to focus unpredictably, leading to uneven sound distribution, echoes, and “hot spots” (e.g., domes, vaulted ceilings).
Concave surfaces create focal points (e.g., domes concentrate sound at specific seats).
Convex surfaces scatter sound but may cause “spatial imbalance” (e.g., “dead zones” in theaters). That means convex surfaces diffuse sound but may cause uneven distribution.
Example :Dome structures in legislative chambers or concert halls may create flutter echoes.
Sound reflection patterns in curved vs. flat surfaces (Source: [3]; Ray-tracing diagram comparing reflections in a semicircular vs. rectangular space. Source: Kuttruff [4]; Insert ray-tracing diagram comparing reflections in a dome vs. a rectangular hall.)
3.2 Reverberation control
High ceilings and hard surfaces contribute to excessive reverberation, reducing speech intelligibility. Curved spaces often exceed “optimal RT” (per ISO 3382-1), degrading speech intelligibility.
Example:
| Space type | Ideal RT (s) | Typical RT in curved spaces (s) |
|---|---|---|
| Auditorium | 1.2–1.8 | 2.5–4.0 |
| Airport terminal | 0.8–1.2 | 1.8–3.0 |
| Atrium | 1.0–1.5 | 2.0–3.5 |
| Space type | Ideal RT (s) | Measured RT in curved spaces (s) | Primary issue |
|---|---|---|---|
| Concert hall | 1.8–2.2 | 2.5–4.0 | “Muddy” music |
| Airport atrium | 0.8–1.2 | 1.5–2.5 | Announcer clarity |
| Legislative chamber | 1.0–1.5 | 2.0–3.0 | Echo interference |
Table 2.
Reverberation time standards vs. real-world curved spaces.
Data sources: ISO 3382-1; Ahnert et al. [6]*.
3.3 Background noise and masking
HVAC systems, crowd noise, and external sound infiltration can degrade acoustic comfort. Low-frequency HVAC rumble is hard to absorb with traditional materials. Crowd noise buildup is due to minimal scattering. These two types of background sound, along with external sound infiltration, are common noise sources for a large room. In a highly reverberant environment, the masking sound is easy to couple with the original sound field and cause a coloration effect (Coloration). For example, when the electronic music generated by the column network of Foguang Temple (target sound source) coexists with the internal noise of the building (such as the footsteps of tourists and environmental noise), the low-frequency noise (< 500 Hz) may cover the details of the musical beat and destroy the integrity of the perception of spatial rhythm.
4. Acoustic physics unique to curved geometries
Acoustic physics refers to the study of sound waves and their behavior in different media. Curved geometries, such as spheres, cylinders, and cones, present unique acoustic properties due to their shape. From an academic perspective, researchers have studied the following aspects of acoustic physics in curved geometries.
4.1 Acoustic resonance
Resonance is a phenomenon that occurs when an object vibrates with a greater amplitude in response to a specific frequency. In acoustics, resonance can appear when a sound wave causes a structure to vibrate. The vibrating structure then radiates a new sound wave, which can be detected by a microphone or a sensor. Curved surfaces can enhance or suppress acoustic resonance frequencies, and a structure vibrates at this frequency with maximum amplitude in response to an applied force or sound wave. For example, a spherical surface has a single resonance frequency, whereas a cylindrical surface has multiple resonance frequencies. The geometry of the surface and resonance frequencies mutually determine, providing a basis for researchers to decide a structure’s shape and properties. It is to indicate that certain frequencies of the sound wave can cause a curved surface with different shapes to vibrate, even more strongly than others, at some specific moments.
4.2 Acoustic diffraction
Diffraction is the bending of a wave around an obstacle. When a sound wave encounters a curved surface, it can reveal significant sound diffraction information about the shape and size of the surface with different patterns, because the amount and direction of the bending depend on the shape and size of the obstacle. This information can be used to design better acoustic devices, such as loudspeakers [7] or microphones, which can operate in curved environments. The wavefront bends when encountering a curved surface obstacle. Diffraction occurs for the reason that the curved surface of the sound wavefront is not a straight line. By analyzing the diffraction pattern of a sound wave around a curved surface, researchers can determine the shape and properties of the surface.
4.3 Acoustic scattering
A wave is reflected or refracted in multiple directions, or absorbed by the surface, when encountering an obstacle, and it scatters. Curved surfaces can cause complex scattering patterns due to the curvature of the surface. By analyzing the scattered wavefronts, researchers can determine the shape, identify features such as cracks, defects, or internal structures, and create images of the surface, especially in a large-scale room.
The amount and direction of the scattering depend on the shape and properties of the surface. Acoustic scattering is also important in underwater acoustics, where sound waves propagate through the ocean floor. The shape of the ocean floor can cause complex scattering patterns that affect the propagation of sound waves. By understanding the acoustic properties of the ocean floor, researchers can design better sonar systems and improve underwater communication.
4.4 Acoustic imaging
By using arrays of microphones or sensors, researchers can create images of curved surfaces based on the acoustic properties of the surface. These images can be used to identify features such as cracks, defects, or internal structures. Acoustic imaging is the process of creating images of an object or a surface based on its acoustic properties. By using arrays of microphones or sensors, researchers can create images of curved surfaces based on the acoustic properties of the surface. These images can be used to identify features such as cracks, defects, or internal structures.
Acoustic imaging is important in biomedical engineering, where curved surfaces are common. For example, the inner surface of the human ear is curved, and acoustic imaging can be used to diagnose and monitor ear diseases. Acoustic imaging is also used in nondestructive testing of materials, where the internal structure of a material can be imaged without damaging it.
4.5 Summary
The study of acoustic physics in curved geometries has important applications in various fields, such as biomedical engineering, underwater acoustics, and nondestructive testing of materials. It gives researchers possible solutions to design better acoustic devices (sonar systems) and improve communication and imaging, diagnose diseases by understanding the acoustic properties of curved surfaces, where curved surfaces are common, and acoustic imaging can be used for noninvasive diagnosis and monitoring of diseases.
5. IEQ acoustic regulations and standards
There are two categories of emphasized regulations on international standards and regional codes to outline from ISO, ANSI, LEED, EU, and ASHRAE in this section.
5.1 International standards
ISO 3382 (Acoustic Quality in Rooms) defines reverberation time (RT), speech clarity (C50), and sound strength (G) in large spaces.
ANSI S12.60 (Classroom Acoustics, extended to public spaces) sets noise level limits (e.g., ≤ 35 dB background noise for optimal speech clarity).
LEED v4.1 (IEQ Credit: Acoustic Performance) encourages sound masking and absorption in large-volume spaces (Table 3).
| Standard | Parameter | Threshold | Curved-space relevance |
|---|---|---|---|
| ISO 3382-1 | Reverberation time (RT) clarity (C50) | RT ≤ 1.5 s (speech) | Critical for domes/atria |
| ANSI S12.60 | Background noise (NC) | NC ≤ 35 (classrooms) | Applies to public lobbies, Airports, and museums |
| LEED v4.1 IEQ | Sound absorption (NRC) and masking required | NRC ≥ 0.75 (ceilings) | Mandates curved-space solutions, large public buildings |
Table 3.
Key acoustic standards for public spaces.
LEED credit breakdown for Acoustic Performance (Source: [8]) focuses Indoor Environmental Quality Category.
Prerequisite: Minimum Acoustic Performance.
EQp: Minimum Acoustical Performance.
Core requirement: Control exterior noise intrusion: Exterior Wall STC ≥ 50 + Window STC ≥ 35.
HVAC noise control: RC/NR ≤ 40 in occupied spaces.
5.2 Credits for acoustical design
EQc: Acoustic performance (1–2 points).
5.3 Option 1: Sound isolation (1 point)
See Table 4.
| Space type | STC/IIC requirement |
|---|---|
| Occupied-occupied spaces | STC ≥ 50, IIC ≥ 50 |
| Occupied-corridors | STC ≥ 45, IIC ≥ 45 |
| Occupied-building services | STC ≥ 55, IIC ≥ 55 |
Table 4.
Sound isolation (1 point).
5.4 Option 2: Background noise and reverberation (1 point)
See Table 5.
| Space type | Max background noise | Max RT60 (500-2 kHz) |
|---|---|---|
| Classrooms/offices | ≤ 35 dBA | ≤ 0.6 sec |
| Conference rooms | ≤ 40 dBA | ≤ 0.7 sec |
| Open-plan offices | ≤ 45 dBA (NC/RC ≤ 40) | ≤ 0.8 sec |
Table 5.
Background noise and reverberation (1 point).
5.5 Option 3: Comprehensive design (2 points)
Achieve both Option 1 + Option 2 requirements.
Additional credits impacting acoustics.
EQc: Thermal comfort (1 point)
Acoustic Link: HVAC noise control (RC/NR ≤ 35) for thermal zoning systems.
EQc: Interior lighting (1: 2 points)
Acoustic link: Specify low-noise luminaires (< 24 dBA in quiet spaces).
MRc: Low-emitting materials (1: 3 points)
Acoustic link: Use acoustic panels/ceilings with VOC emissions ≤ CDPH/EHLB Standard.
As an international standard, LEED credits reflect effective measures both for targeting for single acoustic item and for integrated acoustic performance, so it has particular and broader application in technological response to the acoustic design of curved geometries’ spaces.
5.6 Regional building codes
EU Directive 2020 (Noise Emission Standards) also mandates sound insulation and reverberation control in public buildings. ASHRAE 189.1 (High-Performance Buildings) recommends acoustic treatments for atria and open-plan public spaces.
Sections 5.1 and 5.2 express regulations on large and small different ranges, which cover most considerations and references in the realistic application. Reverberation time (RT), speech clarity (C50), and sound strength (G) are commonly used parameters for large spaces acoustic evaluation. Under the guidance of ISO 3382 and ANSI S12.60 for acoustic quality in the classroom, extended to public spaces, for example, sound-absorbing materials (e.g., low-emitting materials) is one method to complete ANC (sound masking), setting background noise level limits (≤35 dB for optimal speech clarity). Apart from this, hybrid passive-active solutions in engineering comfort to current social green energy-saving trends. Computational acoustic modeling is a predictive way before the construction of a realistic project.
6. New acoustic technologies and design responses
6.1 Advanced sound-absorbing materials
Microperforated Wood Panels (MPP) provide broadband absorption (500–4000 Hz) while maintaining esthetics.
Metamaterials are subwavelength structures for “low-frequency absorption” (e.g., 100–500 Hz). Acoustic cloaking is one technology involving the use of acoustic metamaterials to manipulate the propagation of sound waves. It can be particularly effective in large curved spaces, as it allows sound waves to be bent around obstacles or redirected in a specific direction. One case study is the Beijing National Stadium, also known as the Bird’s Nest, which uses acoustic cloaking to reduce noise levels and improve sound quality in the stadium.
3D-Printed Acoustic Baffles [9] are customizable curved baffles, able to optimize diffusion and absorption. Custom geometries for curved spaces.
Bio-based panels of mycelium composites (NRC 0.9) could be used as sustainable alternatives.
The range of the sound absorption coefficient is taken as the median (Table 6).
| Materials | 125 Hz | 500 Hz | 2 kHz |
|---|---|---|---|
| MPP | 0.22 | 0.75 | 0.55 |
| Fiberglass | 0.33 | 0.95 | 0.95 |
| Foam | 0.12 | 0.70 | 0.80 |
6.2 Active noise control (ANC) and sound masking
Adaptive phased-array ANC systems use phased-array microphones and speakers to cancel low-frequency noise in real time (e.g., Tokyo’s Haneda Airport) [11].
Active noise control: This technology uses microphones and speakers to cancel out unwanted noise in real-time. It can be particularly effective in large curved spaces with high noise levels, such as transportation hubs. One case study is the Schiphol Airport in Amsterdam, which has implemented an active noise control system in its departure lounges to reduce noise levels and improve passenger comfort.
Directional sound masking focuses white noise to improve speech privacy without increasing overall noise levels. “Kinetic Ceilings”: Motorized panels adjust RT dynamically (e.g., Hamburg Elbphilharmonie).
Example: Singapore Changi Airport uses directional sound masking to improve speech privacy.
6.3 Computational acoustic modeling
Wave-based simulation (e.g., COMSOL, Odeon) predicts sound behavior in complex curved geometries before construction. Parametric acoustic design uses algorithms to optimize surface shapes for balanced sound diffusion. It could be simulated as for sound distribution in a curved atrium with Odeon (Source: Rozhin Naeemaee, Zühre Sü Gül [12]).
6.4 Hybrid passive-active solutions
Tunable acoustic metamaterials—Adjustable panels that modify absorption coefficients based on frequency needs.
Kinetic ceiling systems—Mechanically adjustable reflectors/absorbers to adapt to different occupancy conditions.
Undulating ceiling panels for controlled diffusion.
These are just a few examples of the many technologies and case studies that could be highlighted in the chapter. By showcasing these examples, we can provide a practical and insightful overview of the current state of interior acoustic research and the potential of new acoustic technologies in addressing the challenges of large curved spaces in public architecture [13].
7. Case studies
Certainly, here are some specific technologies and case studies that could be highlighted [14, 15, 16]:
7.1 Elbphilharmonie, Hamburg
Challenge: Excessive reflections in the undulating ceiling.
Solution: Parametrically optimized diffusive panels.
The grand concert hall is the heart of the Hamburg Elbphilharmonie. The “white skin” that plays a decisive role in its acoustics is what makes it stand out. This unique wall and ceiling are composed of 10,000 gypsum fiber panels, each individually milled to form a complete surface structure. This allows sound to spread to any corner, delivering an extraordinary acoustic experience.
Acoustic glass: This material is designed to minimize the transmission of sound through glass surfaces. It can be particularly effective in large curved spaces, such as concert halls or auditoriums, where sound isolation is critical. For example, the Elbphilharmonie in Hamburg, Germany, uses acoustic glass to minimize the transmission of sound between the concert hall and the surrounding areas.
Acoustic analysis: The first step in designing the panels was to conduct an acoustic analysis of the space. This involved simulating the acoustic properties of the concert hall and identifying areas where sound reflections could cause problems. Followed by parametric modeling. Using parametric modeling software, designers created a digital model of the concert hall ceiling, finding the problems of diffusion and reflection. Then, optimization: The software’s optimization algorithms were used to find the best panel design (shape, size, and material properties) that would meet the acoustic requirements of the space.
Fabrication: The acoustic glass panels were then fabricated using a combination of digital fabrication techniques and traditional manufacturing methods. The panels’ complex shapes were created using computer-controlled milling machines, while the final assembly was done by hand (Figure 1).
Figure 1.
Acoustic panel arrangement in Elbphilharmonie.
7.2 Singapore Changi airport terminal 5
Technology: Hybrid passive absorption + ANC.
Hybrid passive absorption and ANC technology uses both passive and active noise cancelation techniques (integrated sound-absorbing curved surfaces with ANC) to provide a superior listening experience.
Hybrid passive absorption and Active Noise Cancelation (ANC) technology, typically used in audio devices, has found its way into large-scale architecture to address the issue of noise pollution in busy urban areas. This technology combines passive and active noise cancelation techniques to minimize external noise and create a quiet and peaceful environment inside buildings.
In Singapore Changi Airport Terminal 5, passive noise cancelation techniques are used to design buildings that minimize external noise. This includes using materials that absorb sound, such as acoustic insulation and soundproof glass. Therefore, the design of Terminal 5 itself is also crucial. Generally, large buildings, such as skyscrapers, can create resonance due to their height and shape, leading to increased noise levels. To address this issue, architects use techniques such as vibration isolation and base isolation to decouple the terminal building from the ground and reduce the amount of noise that is transferred.
ANC technology in this terminal uses electronic components to actively cancel out external noise. This includes installing speakers and microphones in this terminal to capture external noise and generate an inverted sound wave that minimizes the amount of noise entering even cancels out the external noise. This technology is particularly useful in areas where passive noise cancelation is not enough, such as in busy urban areas, similar to around Singapore Changi Airport. This hybrid technology ensures that Terminal 5’s users experience a quiet and peaceful environment, free from external noisy distractions in the populated business area (Figure 2).
Figure 2.
Interior look of Singapore Changi Airport Terminal 2,5 (Source: Baidu Pictures).
In conclusion, the benefits of hybrid passive absorption and ANC technology in large-scale architecture are numerous. Some of the key benefits include:
Improved indoor environment: The hybrid technology creates a more peaceful and quiet indoor environment, improving the overall comfort and well-being of the building’s occupants.
Increased productivity: The reduced noise levels inside buildings lead to increased productivity, as occupants can focus better without external noise distractions.
Reduced energy consumption: The passive noise cancelation techniques used in architecture can significantly reduce the amount of energy needed to operate the ANC technology.
7.3 The Walt Disney concert hall in Los Angeles, USA
This hall uses the technology of virtual acoustics.
The acoustic design of the concert hall was handled by acoustics expert Toshiyuki Toyoda (Yasuhisa Toyota). Although its acoustic performance was initially questioned by the architectural community, after several concerts, its excellent sound quality received widespread praise and was considered superior to the other major concert hall at the Los Angeles Music Center, the—Dorothy Chandler Hall (Dorothy Chandler Pavilion).
This technology involves the use of computer simulations to model the acoustic behavior of large curved spaces. It can be particularly effective in the design phase, as it allows architects and acoustic engineers to test different scenarios and optimize the acoustic performance of the space. For example, the Walt Disney Concert Hall in Los Angeles, USA, used virtual acoustics to optimize the acoustic performance of the concert hall before construction (Figure 3).
Figure 3.
Interior look of Walt Disney Concert Hall in Los Angeles (Source: Baidu Pictures).
Table 7 synthesizes the comparison of the three aspects of the existing acoustic problem, applied solutions, and final outcome in three case studies.
| Case 1 Elbphilharmonie, Hamburg | Case 2 Singapore Changi Airport Terminal 5 | Case 3 The Walt Disney Concert Hall in Los Angeles, USA | |
|---|---|---|---|
| Problems | Excessive reflections in the undulating ceiling | Excessive noise | Need to test different scenarios in advance |
| Solutions | Acoustic glass to parametrically optimize diffusive panels | Hybrid passive absorption + ANC | Virtual acoustics, computer simulations |
| Outcomes | Sound spreads to any corner, delivering an extraordinary acoustic experience | Users can experience a quiet and peaceful environment, free from external noisy distractions in the populated business area | Optimize the acoustic performance of the concert hall before construction |
Table 7.
The three case studies comparison (problem, solution, and outcome).
8. Future trends and conclusion
Regulatory compliance and innovative acoustic technologies must work synchronously to enhance IEQ in large curved public spaces. Future research should focus on adaptive systems that dynamically respond to occupancy and usage patterns, for instance, AI-Driven Acoustic Optimization and Neural Network optimization. Machine learning as one AI tool for real-time acoustic adjustments [17] (e.g., real-time RT adjustment via sensor networks) will give more immediate treatment, showing more prospective, better adaptation to the development of the era. Additionally, Neural Network optimization means that AI predicts optimal RT adjustments per occupancy has lit a light into tomorrow. Otherwise, materials are a traditional solution in various industries. Sustainable acoustic materials (bio-based absorbers) they are with low carbon footprints, which have better adaptation due to economic requirements in the long-term use. In addition, biophilic acoustic materials (e.g., mycelium-based sound absorbers) and self-healing acoustic panels (microcapsule-based coatings) repair surface wear. They act very much like a kind of microbial concrete, which could grow in the damaged place.
This chapter is a comprehensive overview of acoustic IEQ in curved large spaces at present, on the basis of acoustic physics theories, making it suitable for a professional book on interior environmental quality. This chapter assists practitioners to clearly recognize acoustic challenges at present, integrates acoustic tests and design regulations involved in this type of architectural space, and provides cutting-edge acoustic upgrading solutions recommendations for this space in an overall perspective, particularly offering specific thoughts for standards formulation and further revision for policymakers. What gaps remain for future research?
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