Acoustic Design Research Articles

Passive Acoustic Metamaterials for Low Frequencies—Theories, Types, Testing, and Future Directions

Metamaterials, engineered to exhibit unique properties, not found in natural materials, are a key focus of modern scientific research. Acoustic metamaterials are designed to manipulate or attenuate acoustic waves. Early designs of acoustic metamaterials show promising results in attenuating sound waves in medium and high‐frequency ranges but lack effectiveness for low frequencies. In recent years, there has been a shift toward the research of passive acoustic metamaterials, designed for low frequencies, with a trend toward additive manufacturing for ease of fabrication. Over 45 acoustic design theories have been reviewed, along with 112 low‐frequency acoustic metamaterials designed in the last 5 years. This comprehensive review ensures the validity and reliability of present findings and equips the knowledge to select the most appropriate acoustic theory, metamaterial type, and testing standards for analyzing metamaterial. The article also discusses computational methods in the design process and compares various existing metamaterial designs and their applications in areas like environmental noise reduction, sound isolation, and other health‐related applications. Finally, it reviews testing methods for experimental verification of acoustic metamaterials. This article aims to steer the future course of metamaterial science by integrating a wide range of research, instilling confidence in the validity and reliability of present findings.

Practical realization of chiral nonlinearity for strong topological protection

Nonlinear topology has been much less inquired compared to its linear counterpart. Existing advances have focused on nonlinearities of limited magnitudes and fairly homogeneous types. As such, the realizations have rarely been concerned with the requirements for nonlinearity. Here we explore nonlinear topological protection by determining nonlinear rules and demonstrate their relevance in real-world experiments. We take advantage of chiral symmetry and identify the condition for its continuation in general nonlinear environments. Applying it to one-dimensional topological lattices, we show possible evolution paths for zero-energy edge states that preserve topologically nontrivial phases regardless of the specifics of the chiral nonlinearities. Based on an acoustic prototype design with non-local nonlinearities, we theoretically, numerically, and experimentally implement the nonlinear topological edge states that persist in all nonlinear degrees and directions without any frequency shift. Our findings unveil a broad family of nonlinearities compatible with topological non-triviality, establishing a solid ground for future drilling in the emergent field of nonlinear topology.

A case study of the effect of a living wall on the indoor acoustic environment

The indoor acoustic environment is important, especially in educational settings where speech intelligibility matters the most. Traditional acoustic treatments are often criticised for lacking aesthetic taste and environmental benefits. This paper examines the effectiveness of a living wall in optimising the acoustic performance of an architectural design studio at Taizhou University. Employing the interrupted noise method, the reverberation times and absorption coefficients before and after installing a living wall, across frequency bands from 100 to 5000 Hz, were measured. The data was used in numerical simulations adopting the Odeon software to predict the acoustic impacts of the living wall of three typical classrooms in the university. The results reveal that the living wall reduced the reverberation time by an average of 0.19–0.47 s in the critical speech frequencies, underscoring its potential as a viable, multifunctional element in architectural acoustic design.

Thermal and Acoustic Design of a Shelter for High-Voltage Electrical Equipment

Thermal and Acoustic Design of a Shelter for High-Voltage Electrical Equipment

A phononic crystal waveguide using surface waves below the sound cone

Surface acoustic waves are commonly used in a variety of radio-frequency electrical devices as a result of their operation at high frequencies and robust nature. For devices based on Rayleigh-like plane waves, functionality is based on the fact that the Rayleigh wave mode is confined at the solid–air interface. However, to create advanced functionality through the use of phononic crystal structures, standard cylindrical inclusions have been shown to couple Rayleigh modes to the shear horizontal bulk modes and provide a significant pathway to energy loss. We introduce alternative inclusion shapes with a reduced two-fold symmetry that lowers the speed of the Rayleigh-like surface acoustic wave to below that of the shear horizontal mode. With an eigenfrequency below the sound line, the mode is confined to the surface with limited coupling and loss to the bulk. Based on these inclusions, an acoustic waveguide design is proposed, which demonstrates a strong confinement of wave energy both at the surface and within the waveguide.

A primer on low-carbon design in architectural acoustics using a case study of residential floorsa).

Designers are increasingly tasked to reduce the carbon footprint of buildings. While core disciplines (e.g., mechanical and structural) are determining sustainable design strategies, understanding the environmental impacts of architectural acoustics is nascent. Yet, acoustic design decisions provide opportunities to minimize building carbon emissions while ensuring suitable acoustic performance. In response, this paper first motivates the need for design synergies between architectural acoustics and sustainability practices. Second, this paper educates and equips acousticians to participate in sustainable design decisions by demonstrating a life cycle assessment framework to inform the selection of low-carbon floor-ceiling assemblies in residential buildings while satisfying sound isolation requirements.

Musical Comfort Evaluation of The Natural Acoustics and Architectural Design of Three Performance Spaces in Kocaeli-Izmit

This study was conducted to evaluate the auditory comfort level of Western art music performances performed in natural acoustic conditions in multi-purpose performance halls, which are widely preferred today, on the listener. In this context, first the reverberation time, one of the acoustic comfort parameters, is expressed and the Sabine formula, which is the empirical method used in the study, is explained. Subsequently, the table "absorptivity coefficients of various materials at different frequencies" is presented, as it will be used in the calculation of reverberation time, and the graph "recommended optimum reverberation time for volume-dependent speech and music" is presented to make comparisons at the end of the calculation. Then, information was given about the geometry of performance spaces and acoustic defects that may occur due to structural errors in closed volumes were explained. After explaining why this study was conducted in Izmit district of Kocaeli province, the selection criteria of the three selected performance halls were explained. After giving brief information about the historical background of each place, the reverberation time of the halls was calculated. As a result of the calculations, the acoustic comfort conditions of the halls in natural acoustics and when used for musical purposes are presented comparatively in the table, and it has been revealed that all three halls will not provide a suitable acoustic comfort experience to the audience. The improvement suggestions that can be made to ensure acoustic comfort during the Western classical music performance without the use of an electro-acoustic system are presented in tables for each hall.

Influence of the Sound Source’s Position on the Stage on the Speech Perception in the Auditorium

Constant efforts to achieve the best possible speech intelligibility during theatre performances were the motivation for the research presented in this article. The acoustic conditions in a theatre hall depend not only on the design of the room acoustics, but also on the stage decoration and the positioning of the sound source (actor) on stage. The ACR (Absolute Category Rating) method recommended by the ITU was used to investigate the influence of the decorations and the position of the speaker on stage on the subjective evaluation of the listeners’ perception of speech. Subjective tests were carried out in situ and in the laboratory based on recordings made in the facility that was the subject of the measurements. An extensive analysis of the results was carried out, taking into account individual aspects of the tests, such as the type of decoration, speaker position, listener position, and the way the recording was made. Based on the discussion of the results, the conclusions are presented.

A reduced-order boundary element method for two-dimensional acoustic scattering

This study presents a novel method for wideband acoustic analysis using the Boundary Element Method (BEM), addressing significant computational challenges. Traditional BEM requires repetitive computations across different frequencies due to the frequency-dependent system matrix, resulting in high computational costs. To overcome this, the Hankel function is expanded into a Taylor series, enabling the separation of frequency-dependent and frequency-independent components in the boundary integral equations. This results in a frequency-independent system matrix, improving computational efficiency. Additionally, the method addresses the issue of full-rank, asymmetric coefficient matrices in BEM, which complicate the solution of system equations over wide frequency ranges, particularly for large-scale problems. A Reduced-Order Model (ROM) is developed using the Second-Order Arnoldi (SOAR) method, which retains the key characteristics of the original Full-Order Model (FOM). The singularity elimination technique is employed to directly compute the strong singular and super-singular integrals in the acoustic equations. Numerical examples demonstrate the accuracy and efficiency of the proposed approach, showing its potential for large-scale applications in noise control and acoustic design, where fast and precise analysis is crucial.

Acoustic Design of a Modular Studio Box for Use as Control and Mixing Room for Immersive Audio

This article presents a detailed analysis of the acoustic design process of a soundproofed box intended for control room and mixing for immersive audio. The main objectives of the project were defined based on the quality criteria required for critical listening environments, particularly for Dolby Atmos rooms. The adopted methodological approach relies on predictive evaluations of key acoustic parameters, supported by studies and calculations conducted using advanced numerical models and software. Key phases of the design process include the optimisation of the box dimensions, the modal analysis for low-frequency response, the design of the listening layout and early reflections, the specification of the internal acoustic treatment. The technical solutions adopted aim to ensure an accessible and cost-effective environment, achieved through optimization in material and space selection while still meeting requirements.

GNSS-A Trajectory Optimization and Its Rose-Curve Solution Regarding Acoustic Delay Parameter Identification

Global Navigation Satellite System (GNSS)-Acoustic (GNSS-A) trajectory design is vitally important for precise seafloor geodetic positioning. However, GNSS-A trajectory optimization based on an ordinary GNSS-A observation model suffers a major setback due to a lack of consideration for the spatio-temporal variations of sound speed. We propose a GNSS-A trajectory optimization criterion based on a GNSS-A observation model appended with acoustic delay parameters characterizing the sound speed variations. In addition, we put the problem into a continuous function space to obtain a concise curve solution that is free from the sampling interval of observations. Particularly, a family of rose trajectory solutions is derived for developing unmanned GNSS-A systems. It shows that the optimal size of the rose trajectory is 2.8 times the water depth for the ordinary observation model, but the optimal size becomes at least 8.3 times the water depth for the observation model with the acoustic delay parameters. The more the parameters used to characterize the time-varying nature of the acoustic delay are adopted, the larger the trajectory size is needed. The proposed trade-off strategy between the cost increase and the precision benefit is recommended to shrink the trajectory size to reduce the ship-time cost and avoid the limitation of signal propagation. The proposed results are verified through the simulation tests and actual measurements. It shows that we should adopt the derived optimal trajectory to ensure the geometric precision of the acoustic delay parameters. The size of the GNSS-A trajectory adopted conventionally is far from the optimal size for inverting the sound speed field structure.

How speech in acoustically different offices influences a working person? – Experiments in two countries

Working during task-irrelevant speech influences workers. Adequate room acoustic design can reduce the negative effects in open-plan offices, but harmonized target values do not exist. Our purpose was to examine the effects of room acoustic design levels on a working person during the exposure to task-irrelevant speech. The Finnish room acoustic regulation was chosen as a reference, as it is one of the strictest worldwide. Three room acoustic conditions were examined: regulation violated (Reg-) (Speech Transmission Index, STI=0.71), regulation fulfilled (Reg0) (STI=0.37), and regulation surpassed (Reg+) (STI=0.16). To examine the generalizability of the results, a similar experiment was performed in two countries (two languages and laboratories): Finland and Germany (FinGer study, N = 98). Experience was measured with questionnaires, performance with visual and auditory serial recall tasks, and physiological stress with heart rate variability. Results did not depend on the country, suggesting that our findings could be similar also in other countries. Speech annoyance and perceived concentration difficulty differed in each condition. With other experience measures, only Reg+ improved experience compared to the two other conditions. Visual serial recall performance was more accurate and faster in Reg+ than in Reg-. Accuracy was also improved in Reg0 compared to Reg-. The physiological stress levels did not depend on the condition. Our study shows that Reg0 was better than Reg- with respect to experience and performance but experience was further improved from Reg0 to Reg+. Therefore, it is beneficial to design room acoustics better than the Finnish regulation to maximize work performance and experience.

Fuselage panel structural-acoustic optimization design of civil aircraft based on numerical analysis

Abstract During the design process of civil aircraft, it is necessary to achieve a high level of cabin noise control to improve cabin comfort. In addition to controlling the intensity of the main noise sources that affect the acoustic environment in the cabin, the acoustic optimization design of the fuselage wall panel structure is also required. In this paper, acoustic analysis software ACTRAN is applied to study the acoustic characteristics of typical structures of civil aircraft cabins. Boundary conditions, material density, and material damping are analyzed from the following main aspects: fuselage panels, thickness, density, reinforced frame design, etc., to study the acoustic barrier performance of typical fuselage panel structures, put forward design suggestions for fuselage panels, and guide the acoustic optimization design of civil aircraft structures.

A novel optical acoustic fabric based on intensity-modulated flexible air-filled fiber adapter for sound sensing

This study proposes and demonstrates an optical acoustic fabric design method to detect sound, which is based on intensity-modulated flexible air-filled fiber adapter (FAFFA). A FAFFA was woven into the weft center of the polyamide fabric as weft, and the FAFFA was realized by connecting polymer optical fibers at each end of an flexible tube. The principle of the optical acoustic fabric is to allow the flexible tube to deform with the resonance of the polyamide fabric, subsequently changing the light intensity in the FAFFA. The macro-scale finite element method and ray tracing optical simulation investigated the operating principle of optical acoustic fabric and performance of FAFFA structures, and the influence of fabric parameters was evaluated by meso-scale finite element simulation. The yarn of the optical fiber acoustic fabric has low Young’s modulus and high flexibility. The proposed FAFFA structure is simple to prepare and has good maneuverability, which breaks away from the constraints of the traditional optical acoustic sensor membrane structure. This proposed optical acoustic fabric is easy to prepare, simple in principle and highly flexible. Along with wireless devices, the use of the optical acoustic fabric can be further extended to “hearing aids” for special individuals in wearable applications.

Acoustic structure inverse design and optimization using deep learning

From ancient to modern times, acoustic structures have been employed to manage the spread of acoustic waves. Nevertheless, designing these structures traditionally remains a laborious and computationally intensive iterative process. Recognizing that complex acoustic systems can be effectively analyzed using the lumped-parameter method, we introduce a deep learning model that learns the correlation between the equivalent electrical parameters and the acoustic properties of these structures. As an illustration, we consider the design of multi-order Helmholtz resonators, showing experimentally that our model can predict structures with high precision that closely align with the specified design criteria. Furthermore, our model can seek multiple solutions in conjunction with dimensionality reduction algorithms and support evolutionary algorithms in optimization tasks. Compared to traditional numerical methods, our approach offers greater efficiency, flexibility, and universality. The designed acoustic structures hold broad potential for applications including speech enhancement, sound absorption, and insulation.

Acoustic performance prediction by means of a statistical energy analysis of two adjacent workrooms used for conferences and educational proposes

The current design of workspaces for companies is focused on minimalistic and modern styles prioritizing the aesthetic appearance with illuminated open spaces and the use of glass walls. If the acoustic performance is not considered, inappropriate Reverberation Times (RT) might lead to difficulties for hearing a speaker or teacher during courses and conferences, causing problems in the learning process. Additionally, there might be high sound transmission between adjacent work rooms. This paper presents the development and experimental validation of numerical models using Statistical Energy Analysis (SEA) to calculate the sound reduction index through a glass wall that separates two adjacent work rooms. These structures are dedicated to conferences and educational uses but cannot be properly used due to their high sound transmission and inappropriate reverberant time. The sound insulation prediction results are validated with experimental measurements carried out in the adjacent rooms under the standard ISO-140. Afterwards, a SEA model is used to provide some acoustic correction design guidelines for these types of constructions. To improve the acoustical performance in the rooms, the acoustic effects of different absorbent panels placed on the walls and ceiling were investigated, choosing a suitable material that complies with the recommended ranges of RT and with less amount of absorption area. The SEA model is then used to understand the effects of openings size between the panels that make up the glass wall on the sound insulation capacity between rooms. Finally, a SEA model is reformulated to quantify the effect of the application of double walls for sound insulation between rooms, which implies the increase of weighted sound reduction index in 9 dB with respect to measured data.

Structural and acoustic behavior of a timber slab with wooden tuned mass dampers

The increasing use of timber in multi-story construction has highlighted challenges related to the vibration behavior of timber floor slabs, affecting both structural and acoustic performance. Floor vibrations between 0 and 20 Hz and structure-borne sound especially between 50 and 100 Hz are impairing the user comfort and serviceability. This paper investigates a mono-material approach using wooden tuned mass dampers (TMDs) to reduce these vibrations in timber slabs, particularly in buildings with long spans. Eigenmodes in relevant frequency ranges are first identified, followed by the separate design and interdisciplinary integration of TMDs for structural and acoustic performance. The study integrates acoustic and structural design requirements through an interdisciplinary process, employing both experimental and numerical models. Results demonstrate that wooden TMDs can address both disciplines and reduce deflection in timber slabs and improve structure-borne and low-frequency sound transmission.

On the development of the first russian-chinese standard in the field of aircraft manufacturing GOST R 70066-2022 «Aircraft equipment. Requirements for aircraft acoustic design of passenger salon and crew cockpit»

The new national standard in the field of aircraft engineering GOST R 70066-2022 "Aircraft equipment. Requirements for aircraft acoustic design of passenger salon and crew cockpit" is reviewed. This standard was the first jointly developed by experts from Russia and China and approved as national standards in the Russia and China ( GB/T 41886-2022). The standard establishes general technical requirements for the acoustic design of the passenger cabin and crew cockpit, as well as requirements for verification of the acoustic design process of passenger cabin and cockpit of transport aircrafts.

Broadband low-transmission study of ventilation metasurfaces based on Archimedean spirals

The primary objectives of acoustic material design include ensuring indoor ventilation and isolating external noise. This study introduces a ventilation metamaterial surface based on Archimedean spirals (ASVM) and calculates its energy transmission coefficient using simulation and the Transfer Matrix Method (TMM). Experimental validation confirms the accuracy of the proposed model, highlighting ASVM’s potential as an effective ventilation metamaterial surface. Subsequently, ASVM is integrated with Helmholtz resonators (HR) to create two new metasurfaces: HR-ASVM without a neck and N-HR-ASVM with a neck. The former exhibits a power transmission coefficient below 0.2 across the broadband range of 1300 Hz to 2500 Hz, while the latter demonstrates superior sound insulation performance (power transmission coefficient below 0.1) from 639 Hz to 2500 Hz, with complete transmission suppression at 710 Hz. Notably, the thickness of N-HR-ASVM at this frequency is only 1/13 of the wavelength. Simulations of the acoustic pressure field and energy flow analyze the mechanisms responsible for low transmission. Finally, the energy transmission coefficient of N-HR-ASVM is experimentally measured and found to align closely with simulation results. This study provides valuable insights into the research on spiral ventilation metamaterial surfaces.

Large commercial business aircraft acoustic design with SEA

As air travel becomes more frequent, customers are demanding a quieter cabin environment. Over the past two decades, Gulfstream has developed a suite of predictive tools based on Statistical Energy Analysis (SEA) to create a quiet cabin on business aircraft. This paper discusses the most recent collaboration between Gulfstream and Jet Aviation to develop an acoustic design for a large commercial business aircraft. SEA analysis played a key role to identify the risks, determine the driving mechanisms, and develop solutions to meet the established target. Besides SEA model development and analysis, this paper will also discuss some unique challenges to this aircraft and some innovations that were developed to mitigate them. One year after the acoustic design was released, flight test data on the completed aircraft confirmed the success of the acoustic design as the quietest cabin to date on the specific aircraft type.