Acoustics

22 pages, 6359 KiB

Open AccessArticle

Development and Testing of an AI-Based Specific Sound Detection System Integrated on a Fixed-Wing VTOL UAV

by Gabriel-Petre Badea, Mădălin Dombrovschi, Tiberius-Florian Frigioescu, Maria Căldărar and Daniel-Eugeniu Crunteanu

Acoustics 2025, 7(3), 48; https://doi.org/10.3390/acoustics7030048 - 30 Jul 2025

Abstract

This study presents the development and validation of an AI-based system for detecting chainsaw sounds, integrated into a fixed-wing VTOL UAV. The system employs a convolutional neural network trained on log-mel spectrograms derived from four sound classes: chainsaw, music, electric drill, and human [...] Read more.

This study presents the development and validation of an AI-based system for detecting chainsaw sounds, integrated into a fixed-wing VTOL UAV. The system employs a convolutional neural network trained on log-mel spectrograms derived from four sound classes: chainsaw, music, electric drill, and human voices. Initial validation was performed through ground testing. Acoustic data acquisition is optimized during cruise flight, when wing-mounted motors are shut down and the rear motor operates at 40–60% capacity, significantly reducing noise interference. To address residual motor noise, a preprocessing module was developed using reference recordings obtained in an anechoic chamber. Two configurations were tested to capture the motor’s acoustic profile by changing the UAV’s orientation relative to the fixed microphone. The embedded system processes incoming audio in real time, enabling low-latency classification without data transmission. Field experiments confirmed the model’s high precision and robustness under varying flight and environmental conditions. Results validate the feasibility of real-time, onboard acoustic event detection using spectrogram-based deep learning on UAV platforms, and support its applicability for scalable aerial monitoring tasks. Full article

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14 pages, 1717 KiB

Open AccessArticle

Development of Floor Structures with Crumb Rubber for Efficient Floor Impact Noise Reduction

by Ji-Hoon Park and Chan-Hoon Haan

Acoustics 2025, 7(3), 47; https://doi.org/10.3390/acoustics7030047 - 29 Jul 2025

Abstract

Korea has a high population density, considering the size of its territory. Therefore, the importance of convenient and comfortable apartment buildings and high-rise residential–commercial complex buildings has been rising. In addition, because of the improvement in the standard of living along with continuous [...] Read more.

Korea has a high population density, considering the size of its territory. Therefore, the importance of convenient and comfortable apartment buildings and high-rise residential–commercial complex buildings has been rising. In addition, because of the improvement in the standard of living along with continuous national economic growth, the interest in well-being and the expectation of a quiet life with a comfortable and pleasant residential environment have also been increasing. However, Koreans have a lifestyle involving sitting on the floor, so floor impact noise has been occurring more and more frequently. Because of this, neighborly disputes have been a serious social problem. And lately, damage and disputes from noise between floors have been increasing much more. The present work, therefore, used waste tire chips as a resilient material for reducing floor impact noise in order to recycle waste tires effectively. Also, a compounded resilient material, which combines EPS (expanded polystyrene), a flat resilient material on the upper part, with waste tire chips for the lower part, was developed. After constructing waste tire chips at a standardized test building, experiments with both light-weight and heavy-weight floor impact noise were performed. The tests confirmed that waste tire chips, when used as a resilient material, can effectively reduce both light-weight and heavy-weight floor impact noise. Full article

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26 pages, 2471 KiB

Open AccessSystematic Review

Indoor Soundscape Intervention (ISI) Criteria for Architectural Practice: A Systematic Review with Grounded Theory Analysis

by Uğur Beyza Erçakmak Osma and Papatya Nur Dökmeci Yörükoğlu

Acoustics 2025, 7(3), 46; https://doi.org/10.3390/acoustics7030046 - 28 Jul 2025

Abstract

Indoor soundscape is a relatively new and developing field compared to urban soundscape in practice. To address this gap, this study aims to identify the key influencing factors as a first step of the indoor soundscape intervention approach. The study employed a two-phase [...] Read more.

Indoor soundscape is a relatively new and developing field compared to urban soundscape in practice. To address this gap, this study aims to identify the key influencing factors as a first step of the indoor soundscape intervention approach. The study employed a two-phase methodology. Phase one involved a Systematic Review (SR) of the literature, conducted through the PRISMA 2020 guidelines, to collate data on the influencing factors and intervention criteria of the indoor soundscape approach. Searching was conducted using two databases, Web of Science and Scopus. As a result of the search, a total of 29 studies were included in the review. The review included studies addressing the soundscape influencing factors and theoretical frameworks. Studies that did not address these criteria were excluded. Phase two comprised the application of the Grounded Theory (GT) coding process to organize, categorize, and merge the data collected in phase one. As a result of the coding process, three levels of categories were achieved; L1: key concept, L2: overarching category, L3: core category. Four core categories were identified as ‘Sound’, ‘People’, ‘Building’, and ‘Environment’ by proposing the Indoor Soundscape Intervention (ISI) criteria. The repeatable and updatable nature of the proposed method allows it to be adapted to further studies and different contexts/cases. Full article

(This article belongs to the Special Issue Indoor Soundscape: Integrating Sound, Experience and Architecture (2nd Edition))

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12 pages, 1597 KiB

Open AccessArticle

Effects of Anthropogenic Vibratory Noise on Plant Development and Herbivory

by Estefania Velilla, Laura Bellato, Eleanor Collinson and Wouter Halfwerk

Acoustics 2025, 7(3), 45; https://doi.org/10.3390/acoustics7030045 - 25 Jul 2025

Abstract

Anthropogenic infrastructure, such as inland wind turbines commonly found in agricultural fields, has substantially increased subterranean vibratory noise in the past decades. Plants, being rooted in soil, are continuously exposed to these vibrations, yet we have little understanding of how vibrational noise affects [...] Read more.

Anthropogenic infrastructure, such as inland wind turbines commonly found in agricultural fields, has substantially increased subterranean vibratory noise in the past decades. Plants, being rooted in soil, are continuously exposed to these vibrations, yet we have little understanding of how vibrational noise affects plant development and, consequently, plant–insect interactions. Here, we examine the impact of windmill-like vibrational noise on the growth of Pisum sativum and its full-factorial interaction with the generalist herbivore Spodoptera exigua. Plants were exposed to either high or low vibrational noise from seed germination to the seed production stage. We recorded germination, flowering, fruiting time, and daily shoot length. Additionally, we measured herbivory intensity by Spodoptera exigua caterpillars placed on a subset of plants. Plants exposed to high vibrational noise grew significantly faster and taller than those in the low-noise treatment. Additionally, we found a marginally significant trend for earlier flowering in plants exposed to high noise. We did not find a significant effect of vibrational noise on herbivory. Our results suggest that underground vibrational noise can influence plant growth rates, which may potentially have ecological and agricultural implications. Faster growth may alter interspecific competition and shift trade-offs between growth and defense. Understanding these effects is important in assessing the broader ecological consequences of renewable energy infrastructure. Full article

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32 pages, 9845 KiB

Open AccessArticle

Real-Time Analysis of Millidecade Spectra for Ocean Sound Identification and Wind Speed Quantification

by Mojgan Mirzaei Hotkani, Bruce Martin, Jean Francois Bousquet and Julien Delarue

Acoustics 2025, 7(3), 44; https://doi.org/10.3390/acoustics7030044 - 24 Jul 2025

Abstract

This study introduces an algorithm for quantifying oceanic wind speed and identifying sound sources in the local underwater soundscape. Utilizing low-complexity metrics like one-minute spectral kurtosis and power spectral density levels, the algorithm categorizes different soundscapes and estimates wind speed. It detects rain, [...] Read more.

This study introduces an algorithm for quantifying oceanic wind speed and identifying sound sources in the local underwater soundscape. Utilizing low-complexity metrics like one-minute spectral kurtosis and power spectral density levels, the algorithm categorizes different soundscapes and estimates wind speed. It detects rain, vessels, fin and blue whales, as well as clicks and whistles from dolphins. Positioned as a foundational tool for implementing the Ocean Sound Essential Ocean Variable (EOV), it contributes to understanding long-term trends in climate change for sustainable ocean health and predicting threats through forecasts. The proposed soundscape classification algorithm, validated using extensive acoustic recordings (≥32 kHz) collected at various depths and latitudes, demonstrates high performance, achieving an average precision of

89 %

and an average recall of

86.59 %

through optimized parameter tuning via a genetic algorithm. Here, wind speed is determined using a cubic function with power spectral density (PSD) at 6 kHz and the MASLUW method, exhibiting strong agreement with satellite data below 15 m/s. Designed for compatibility with low-power electronics, the algorithm can be applied to both archival datasets and real-time data streams. It provides a straightforward metric for ocean monitoring and sound source identification. Full article

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16 pages, 4224 KiB

Open AccessArticle

Optimizing Museum Acoustics: How Absorption Magnitude and Surface Location of Finishing Materials Influence Acoustic Performance

by Milena Jonas Bem and Jonas Braasch

Acoustics 2025, 7(3), 43; https://doi.org/10.3390/acoustics7030043 - 11 Jul 2025

Abstract

The architecture of contemporary museums often emphasizes visual aesthetics, such as large volumes, open-plan layouts, and highly reflective finishes, resulting in acoustic challenges, such as excessive reverberation, poor speech intelligibility, elevated background noise, and reduced privacy. This study quantified the impact of surface—specific [...] Read more.

The architecture of contemporary museums often emphasizes visual aesthetics, such as large volumes, open-plan layouts, and highly reflective finishes, resulting in acoustic challenges, such as excessive reverberation, poor speech intelligibility, elevated background noise, and reduced privacy. This study quantified the impact of surface—specific absorption treatments on acoustic metrics across eight gallery spaces. Room impulse responses calibrated virtual models, which simulated nine absorption scenarios (low, medium, and high on ceilings, floors, and walls) and evaluated reverberation time (T₂₀), speech transmission index (STI), clarity (C₅₀), distraction distance (r_D), Spatial Decay Rate of Speech (D_2,S), and Speech Level at 4 m (L_p,A,S,4m). The results indicate that going from concrete to a wooden floor yields the most rapid T₂₀ reductions (up to −1.75 s), ceiling treatments deliver the greatest STI and C₅₀ gains (e.g., STI increases of +0.16), and high-absorption walls maximize privacy metrics (D_2,S and L_p,A,S,4m). A linear regression model further predicted the STI from T₂₀, total absorption (Sabins), and room volume, with an 84.9% conditional R², enabling ±0.03 accuracy without specialized testing. These findings provide empirically derived, surface-specific “first-move” guidelines for architects and acousticians, underscoring the necessity of integrating acoustics early in museum design to balance auditory and visual objectives and enhance the visitor experience. Full article

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29 pages, 9956 KiB

Open AccessArticle

Improving the Acoustics of the Church of Saints Marcellino and Pietro in Cremona (Italy) for Musical Performances

by Sofia Parrinelli, Riccardo Giampiccolo, Angelo Giuseppe Landi and Fabio Antonacci

Acoustics 2025, 7(3), 42; https://doi.org/10.3390/acoustics7030042 - 8 Jul 2025

Abstract

Churches are spaces designed with a unique acoustic identity, which is intimately connected to the oratory and musical needs of the historical period in which they were built. For instance, their typically long reverberation time is appropriate to specific uses, such as liturgical [...] Read more.

Churches are spaces designed with a unique acoustic identity, which is intimately connected to the oratory and musical needs of the historical period in which they were built. For instance, their typically long reverberation time is appropriate to specific uses, such as liturgical functions and choral music performances, but it may impair the repurposing of the space for other functions. Indeed, an acoustic environment suitable for choral or sacred music may not be compatible with other musical genres such as chamber music, solo performances, or small instrumental ensembles, which require greater clarity and frequency-balanced acoustic properties. In such cases, careful analysis of the environment and specific acoustic conditioning become essential steps to enable the space to be used for novel purposes, without compromising its artistic and historical integrity. In this work, we analyze and improve the acoustics of the church of Saints Marcellino and Pietro through space-time acoustic measurements and simulations. After developing and validating our model, we propose various solutions to optimize the church acoustics, transforming it into a functional concert hall while preserving its original identity and artistic grandeur. Full article

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16 pages, 8603 KiB

Open AccessArticle

Acoustic Noise Characterization of a Switched Reluctance Motor Using Sound Power and Psychoacoustic Metric Measurements

by Moien Masoumi and Berker Bilgin

Acoustics 2025, 7(3), 41; https://doi.org/10.3390/acoustics7030041 - 27 Jun 2025

Abstract

This paper presents an experimental acoustic noise characterization of a switched reluctance motor (SRM) designed for a wind turbine pitch angle control application. It details the fixture design for holding and positioning the sound intensity probes, along with the essential hardware setup for [...] Read more.

This paper presents an experimental acoustic noise characterization of a switched reluctance motor (SRM) designed for a wind turbine pitch angle control application. It details the fixture design for holding and positioning the sound intensity probes, along with the essential hardware setup for conducting acoustic noise experiments. Additionally, the software configuration is described to ensure compliance with specific measurement requirements. To study the effect of speed and load variations on the motor’s acoustic noise characteristics, tests are conducted at various operating points. The tests employ pulse-width modulation (PWM) current control, operating at a switching frequency of 12.5 kHz. Sound pressure and sound intensity are measured across different operating conditions to determine the sound power and psychoacoustic metrics. Furthermore, the effect of different factors on the motor’s sound power level, as well as on psychoacoustic metrics such as sharpness, loudness, and roughness, is analyzed and discussed. Full article

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11 pages, 1497 KiB

Open AccessArticle

Experimental Investigation of Bulk Elastic Wave Propagation in the Volume of Metamaterials

by Aleksandr Korobov, Natalia Shirgina, Aleksey Kokshaiskii, Natalia Odina and Aleksandr Volodarskii

Acoustics 2025, 7(3), 40; https://doi.org/10.3390/acoustics7030040 - 26 Jun 2025

Abstract

This paper presents the results of experimental studies on the propagation of longitudinal and transverse ultrasonic waves through a metamaterial—a composite material based on polymer matrix with periodically arranged cylindrical elements. Such structures are known as phononic crystals. Amplitude–frequency characteristics were measured for [...] Read more.

This paper presents the results of experimental studies on the propagation of longitudinal and transverse ultrasonic waves through a metamaterial—a composite material based on polymer matrix with periodically arranged cylindrical elements. Such structures are known as phononic crystals. Amplitude–frequency characteristics were measured for phononic crystals with air and metal cylindrical elements, for both longitudinal waves (in the frequency range from 1.5 to 3 MHz) and transverse waves (in the range from 0.2 to 1.2 MHz). A twofold decrease in the amplitude of the transmitted longitudinal ultrasonic wave was experimentally demonstrated in the passband centered at 1.87 MHz during rotation of the phononic crystal. It was also found that the polarization angle of the transverse ultrasonic wave influences the localization of band gaps and passbands. Band gaps, characterized by amplitude minima near 240 kHz, 290 kHz, and 830 kHz and observed for waves polarized parallel to the crystal axis, are replaced by passbands when the wave is polarized perpendicularly. These results suggest the potential for developing analog ultrasonic frequency filters tunable by the angle of rotation. Full article

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20 pages, 3108 KiB

Open AccessArticle

Energy-Efficient MAC Protocol for Underwater Sensor Networks Using CSMA/CA, TDMA, and Actor–Critic Reinforcement Learning (AC-RL) Fusion

by Wazir Ur Rahman, Qiao Gang, Feng Zhou, Muhammad Tahir, Wasiq Ali, Muhammad Adil, Sun Zong Xin and Muhammad Ilyas Khattak

Acoustics 2025, 7(3), 39; https://doi.org/10.3390/acoustics7030039 - 25 Jun 2025

Abstract

Due to the dynamic and harsh underwater environment, which involves a long propagation delay, high bit error rate, and limited bandwidth, it is challenging to achieve reliable communication in underwater wireless sensor networks (UWSNs) and network support applications, like environmental monitoring and natural [...] Read more.

Due to the dynamic and harsh underwater environment, which involves a long propagation delay, high bit error rate, and limited bandwidth, it is challenging to achieve reliable communication in underwater wireless sensor networks (UWSNs) and network support applications, like environmental monitoring and natural disaster prediction, which require energy efficiency and low latency. To tackle these challenges, we introduce AC-RL-based power control (ACRLPC), a novel hybrid MAC protocol that can efficiently integrate Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)-based MAC and Time Division Multiple Access (TDMA) with Actor–Critic Reinforcement Learning (AC-RL). The proposed framework employs adaptive strategies, utilizing adaptive power control and intelligent access methods, which adjust to fluctuating conditions on the network. Harsh and dynamic underwater environment performance evaluations of the proposed scheme confirm a significant outperformance of ACRLPC compared to the current protocols of FDU-MAC, TCH-MAC, and UW-ALOHA-QM in all major performance measures, like energy consumption, throughput, accuracy, latency, and computational complexity. The ACRLPC is an ultra-energy-efficient protocol since it provides higher-grade power efficiency by maximizing the throughput and limiting the latency. Its overcoming of computational complexity makes it an approach that greatly relaxes the processing requirement, especially in the case of large, scalable underwater deployments. The unique hybrid architecture that is proposed effectively combines the best of both worlds, leveraging TDMA for reliable access, and the flexibility of CSMA/CA serves as a robust and holistic mechanism that meets the desired enablers of the system. Full article

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25 pages, 5011 KiB

Open AccessReview

Mapping Soundscape Research: Authors, Institutions, and Collaboration Networks

by Andy W. L. Chung and Wai Ming To

Acoustics 2025, 7(2), 38; https://doi.org/10.3390/acoustics7020038 - 19 Jun 2025

Abstract

Soundscape is the sonic environment that a living being, like a human or animal, experiences in a certain setting. It affects how a space functions and how the being perceives its quality. Consequently, the soundscape is crucial in ecosystems globally. In recent decades, [...] Read more.

Soundscape is the sonic environment that a living being, like a human or animal, experiences in a certain setting. It affects how a space functions and how the being perceives its quality. Consequently, the soundscape is crucial in ecosystems globally. In recent decades, researchers have explored soundscapes using various methodologies across different disciplines. This study aims to provide a brief overview of the soundscape research history, pinpoint key authors, institutions, and collaboration networks, and identify trends and main themes through a bibliometric analysis. A search in the Scopus database on 26 February 2025 found 5825 articles, reviews, and conference papers on soundscape published from 1985 to 2024. The analysis indicated a significant increase in soundscape publications, rising from 1 in 1985 to 19 in 2002, and reaching 586 in 2024. J. Kang was the most prolific author with 265 publications, while University College London emerged as the most productive institution. Co-citation analysis revealed three research groups: one focused on urban soundscapes, another on aquatic soundscapes, and a third on soundscapes in landscape ecology. The keyword co-occurrence analysis identified three themes: “soundscape(s), acoustic environment, and urban planning”, “noise, animal(s), bioacoustics, biodiversity, passive acoustic monitoring, fish, and bird(s)”, and “human(s), sound, perception, and physiology”. Full article

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17 pages, 988 KiB

Open AccessArticle

A Low-Complexity Versatile Beamforming Method for Multiple Parametric Arrays

by Haokang Shi, Jie Shi, Bo Fan and Haoyang Zhang

Acoustics 2025, 7(2), 37; https://doi.org/10.3390/acoustics7020037 - 18 Jun 2025

Abstract

The application of multiple parametric arays (MPAs) has been increasingly prominent in recent years due to the high directivity of parametric arrays. However, existing beamforming methods for MPAs are limited to special scenarios, such as narrow-edged beamforming, or have high complexity, such as [...] Read more.

The application of multiple parametric arays (MPAs) has been increasingly prominent in recent years due to the high directivity of parametric arrays. However, existing beamforming methods for MPAs are limited to special scenarios, such as narrow-edged beamforming, or have high complexity, such as requiring numerous acoustic transfer function (ATF) identifications. This paper proposes a low-complexity versatile beamforming method based on the transitive relationship among ATFs. For N parametric arrays, the number of identified ATFs can be reduced from N² to N through interpolation and flipping. Moreover, by neglecting the less affected part in the acoustic field structure, the number of identified ATFs can be reduced to less than N. On the basis of ATF matrix estimated, the desired acoustic field can be generated by optimizing the emission weight coefficient. The accuracy of ATF estimation is verified through the precise reconstruction of the acoustic field. Even when the number of identified ATFs does not exceed N, the desired acoustic field of different types of beam patterns can be formed correctly. The beamforming effects of MPAs confirm the low-complexity and versatility of the proposed method, offering a highly feasible solution for acoustic field control. Full article

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16 pages, 4737 KiB

Open AccessArticle

Horn Use Patterns and Acoustic Characteristics in Congested Urban Traffic: A Case Study of Ho Chi Minh City

by Thulan Nguyen, Yuya Nishimura and Sohei Nishimura

Acoustics 2025, 7(2), 36; https://doi.org/10.3390/acoustics7020036 - 16 Jun 2025

Abstract

Motorcycle horns are a dominant source of urban noise in many Southeast Asian cities, driven by high two-wheeler density and limited public transport infrastructure. Although automobiles have been in use for over a century, regulations governing horn design and volume control remain inadequate. [...] Read more.

Motorcycle horns are a dominant source of urban noise in many Southeast Asian cities, driven by high two-wheeler density and limited public transport infrastructure. Although automobiles have been in use for over a century, regulations governing horn design and volume control remain inadequate. This study investigates horn use behavior in Vietnamese urban traffic, identifying distinct acoustic patterns categorized as “attention” and “warning” signals. Measurements conducted in an anechoic chamber reveal that these patterns can increase sound pressure levels by up to 17 dB compared to standard horn use, with notable differences in frequency components. These levels often exceed the daytime noise thresholds recommended by the World Health Organization (WHO), indicating potential risks for adverse health outcomes, such as elevated stress, hearing damage, sleep disturbance, and cardiovascular effects. The findings are contextualized within broader efforts to manage traffic noise in rapidly developing urban areas. Drawing parallels with studies on aircraft noise exposure in Japan, this study suggests that long-term exposure, rather than peak noise levels alone, plays a critical role in shaping community sensitivity. The study results support the need for updated noise regulations that address both the acoustic and perceptual dimensions of road traffic noise. Full article

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18 pages, 3915 KiB

Open AccessArticle

An Image Entropy Recurrence Map-Based Screening Method for Ultrasound B-Scan Image Segments Containing Defects

by Peiqiang Chen, Qunli Lishen, Bin Tang and Chenlong Yang

Acoustics 2025, 7(2), 35; https://doi.org/10.3390/acoustics7020035 - 11 Jun 2025

Abstract

In recent years, defect detection based on ultrasound B-scan images has been widely utilized in industry to detect the quality and presence of defects in products. However, there are still some difficulties in the process of processing B-scan images, such as sampling noise, [...] Read more.

In recent years, defect detection based on ultrasound B-scan images has been widely utilized in industry to detect the quality and presence of defects in products. However, there are still some difficulties in the process of processing B-scan images, such as sampling noise, the large amount of data, and so on. In this paper, we analyze the acoustic characteristics of an ultrasound B-scan image time series, design an image preprocessing method to make the image information gray-scale lossless, and propose a screening method for ultrasound B-scan image segments containing defects based on the theory of image entropy and a recurrence diagram. Comparison experiments between this method and the traditional image entropy screening algorithm show that this method can solve the above difficulties to a certain extent and has its own superiority. The method proposed in this paper provides a new idea for processing ultrasound B-scan image sequences and presents a new choice when the traditional method is limited. Full article

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18 pages, 13439 KiB

Open AccessArticle

Experimental Investigation into the Active Narrowband Reshaping of a Ship Model’s Acoustic Signature

by Steffen Ungnad, Delf Sachau, Carsten Zerbs, Andreas Müller and Anton Homm

Acoustics 2025, 7(2), 34; https://doi.org/10.3390/acoustics7020034 - 7 Jun 2025

Abstract

The use of inertial actuators to control the radiated sound pressure of a steel ship model at a lake measurement facility is examined. Therefore, methods of active vibration control as well as active control of target sound fields are applied using a fixed [...] Read more.

The use of inertial actuators to control the radiated sound pressure of a steel ship model at a lake measurement facility is examined. Therefore, methods of active vibration control as well as active control of target sound fields are applied using a fixed configuration of twelve accelerometers, eight control actuators, and five hydrophones. A narrowband feedforward active control system is used to manipulate the sound pressure at hydrophone positions, focusing not only on reducing but also on adding spectral lines in the radiated signature. The performance is assessed using measured data by additional accelerometers inside the ship model as well as by hydrophones surrounding the measurement facility. It is found that less control effort is necessary for the generation of additional tones compared to the control of a present disturbance at hydrophones. In the frequency range considered (below 500 Hz), the actively induced change in the mean structural velocity is not necessarily proportional to the change in the radiated sound pressure. In contrast to the vibration velocity, no unwanted amplification of the sound pressure is found for the frequencies observed. Full article

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28 pages, 13595 KiB

Open AccessArticle

Open-Set Recognition of Environmental Sound Based on KDE-GAN and Attractor–Reciprocal Point Learning

by Jiakuan Wu, Nan Wang, Huajie Hong, Wei Wang, Kunsheng Xing and Yujie Jiang

Acoustics 2025, 7(2), 33; https://doi.org/10.3390/acoustics7020033 - 28 May 2025

Abstract

While open-set recognition algorithms have been extensively explored in computer vision, their application to environmental sound analysis remains understudied. To address this gap, this study investigates how to effectively recognize unknown sound categories in real-world environments by proposing a novel Kernel Density Estimation-based [...] Read more.

While open-set recognition algorithms have been extensively explored in computer vision, their application to environmental sound analysis remains understudied. To address this gap, this study investigates how to effectively recognize unknown sound categories in real-world environments by proposing a novel Kernel Density Estimation-based Generative Adversarial Network (KDE-GAN) for data augmentation combined with Attractor–Reciprocal Point Learning for open-set classification. Specifically, our approach addresses three key challenges: (1) How to generate boundary-aware synthetic samples for robust open-set training: A closed-set classifier’s pre-logit layer outputs are fed into the KDE-GAN, which synthesizes samples mapped to the logit layer using the classifier’s original weights. Kernel Density Estimation then enforces Density Loss and Offset Loss to ensure these samples align with class boundaries. (2) How to optimize feature space organization: The closed-set classifier is constrained by an Attractor–Reciprocal Point joint loss, maintaining intra-class compactness while pushing unknown samples toward low-density regions. (3) How to evaluate performance in highly open scenarios: We validate the method using UrbanSound8K, AudioEventDataset, and TUT Acoustic Scenes 2017 as closed sets, with ESC-50 categories as open-set samples, achieving AUROC/OSCR scores of 0.9251/0.8743, 0.7921/0.7135, and 0.8209/0.6262, respectively. The findings demonstrate the potential of this framework to enhance environmental sound monitoring systems, particularly in applications requiring adaptability to unseen acoustic events (e.g., urban noise surveillance or wildlife monitoring). Full article

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14 pages, 5518 KiB

Open AccessArticle

Experimental and Theoretical Acoustic Performance of Esparto Grass Fibers

by Rubén Maderuelo-Sanz and Juan Miguel Meneses-Rodríguez

Acoustics 2025, 7(2), 32; https://doi.org/10.3390/acoustics7020032 - 25 May 2025

Abstract

Nowadays, natural fiber-based materials are widely used in the building sector, where the use of green and sustainable products is of growing interest. One of these fibrous materials is the esparto, a plant belonging to the Gramineae family, with a height up to [...] Read more.

Nowadays, natural fiber-based materials are widely used in the building sector, where the use of green and sustainable products is of growing interest. One of these fibrous materials is the esparto, a plant belonging to the Gramineae family, with a height up to 1 m. It grows in arid places with scarce rainfall, being common in some areas of the Iberian Peninsula. Due to its morphology, it can be used to replace conventional materials used in soundproofing and building applications. In this work, the acoustic properties of esparto fibers are studied using impedance tube measurements and via a phenomenological acoustic model where the input parameters are some non-acoustic properties such as porosity, density, tortuosity, and flow resistivity. The experimental results obtained showed the good acoustic performance of esparto fibers, with a high sound absorption coefficient along the usual frequency bandwidth. Furthermore, the theoretical results obtained using the phenomenological model exhibited a strong correlation with the sound absorption spectra obtained through experimental measurements. Full article

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20 pages, 3567 KiB

Open AccessArticle

Methodology for Testing Acoustic Absorption of Lightweight Fabrics with 3D Microstructures Using Impedance Tube

by David Caballol, Mónica Morales-Segura and Alejandro Morgado

Acoustics 2025, 7(2), 31; https://doi.org/10.3390/acoustics7020031 - 23 May 2025

Abstract

In this study, the limits of using the impedance tube, or Kundt tube, are examined using the two-microphone method to obtain the normal acoustic absorption coefficient when analyzing the sound absorption properties of lightweight acoustic fabrics. Lightweight porous fabrics with 3D microstructures that [...] Read more.

In this study, the limits of using the impedance tube, or Kundt tube, are examined using the two-microphone method to obtain the normal acoustic absorption coefficient when analyzing the sound absorption properties of lightweight acoustic fabrics. Lightweight porous fabrics with 3D microstructures that have been previously evaluated in reverberation chambers are used. For these materials, a test methodology will be developed in the impedance tube that aims to replicate the conditions of the tests carried out in the reverberation chamber. The samples are tested maintaining the same separation from the final rigid wall and are placed in the impedance tube in two different ways: first, exposing the flat samples to the wave, and second, in pleated format. The results show that it is not possible to consider the results obtained with both methodologies in samples of light textiles with three-dimensional microstructures to be the same. The similarity is limited to low frequencies (100–315 Hz) but bias, excessive dispersion of the data, different global results and shape indicators obtained suggest that both methods are not identical. Full article

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12 pages, 1391 KiB

Open AccessArticle

Speech Intelligibility in Virtual Avatars: Comparison Between Audio and Audio–Visual-Driven Facial Animation

by Federico Cioffi, Massimiliano Masullo, Aniello Pascale and Luigi Maffei

Acoustics 2025, 7(2), 30; https://doi.org/10.3390/acoustics7020030 - 23 May 2025

Abstract

Speech intelligibility (SI) is critical in effective communication across various settings, although it is often compromised by adverse acoustic conditions. In noisy environments, visual cues such as lip movements and facial expressions, when congruent with auditory information, can significantly enhance speech perception and [...] Read more.

Speech intelligibility (SI) is critical in effective communication across various settings, although it is often compromised by adverse acoustic conditions. In noisy environments, visual cues such as lip movements and facial expressions, when congruent with auditory information, can significantly enhance speech perception and reduce cognitive effort. In an ever-growing diffusion of virtual environments, communicating through virtual avatars is becoming increasingly prevalent, thus requiring a comprehensive understanding of these dynamics to ensure effective interactions. The present study used Unreal Engine’s MetaHuman technology to compare four methodologies used to create facial animation: MetaHuman Animator (MHA), MetaHuman LiveLink (MHLL), Audio-Driven MetaHuman (ADMH), and Synthetized Audio-Driven MetaHuman (SADMH). Thirty-six word pairs from the Diagnostic Rhyme Test (DRT) were used as input stimuli to create the animations and to compare them in terms of intelligibility. Moreover, to simulate a challenging background noise, the animations were mixed with a babble noise at a signal-to-noise ratio of −13 dB (A). Participants assessed a total of 144 facial animations. Results showed the ADMH condition to be the most intelligible among the methodologies used, probably due to enhanced clarity and consistency in the generated facial animations, while eliminating distractions like micro-expressions and natural variations in human articulation. Full article

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Acoustics

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