Acoustics

In this paper, a modal decomposition method is employed to analyze the properties of Rayleigh–Lamb waves propagating in an isotropic plate containing an open surface-breaking crack. The mode conversion coefficients (MCCs) are calculated as functions of crack depth and ultrasonic frequency for both an incident Lamb wave. Compared with the incident A0 mode, the MCC of the S0 mode exhibits a less smooth dependence on the phase of the crack modulated. The experimental, finite element method (FEM) and analytical results confirm that crack characteristics can be quantitatively evaluated from the Lamb wave mode conversion indued by the crack. This finding is beneficial for interpreting the detected ultrasonic signals in scenarios involving crack measurements between different waves, such as the modulation of the probing wave’s MCC by the material response in a tensile test machine. Full article

Temperature-dependent characterization of nanomaterials is commonly performed through electrical measurements, and many temperature-sensing applications similarly rely on electrical readout signals. Although these approaches are simple and widely used, they require direct sample contact and may lose sensitivity when the electrical response is weak, saturated, or only weakly dependent on temperature. In this study, a photoacoustic (PA) measurement system was used to evaluate the temperature-dependent response of AgNW networks. PA measurement system detects ultrasonic waves generated through transient thermoelastic expansion after optical absorption, which enables sensitive probing of temperature-dependent optothermal responses beyond conventional electrical measurements. Silver nanowire (AgNW) films with different surface coverage were fabricated through one to four repeated spin-coating cycles using a 1% AgNW ethanol dispersion containing nanowires with diameters of 20–40 nm and lengths of 10–20 µm. The photoacoustic (PA) signals of the fabricated films were measured at various temperatures using a customized PA measurement system and were compared with sheet resistance values obtained using a four-point probe. Both sheet resistance and PA signals increased with increasing temperature, regardless of AgNW surface coverage. Notably, AgNW films with higher surface coverages showed only weak temperature dependence in sheet resistance but pronounced temperature-dependent PA response. These results indicate that PA analysis is particularly useful for characterizing AgNW networks with higher surface coverage, including those used in stretchable electrodes. All samples showed linear relationships for both sheet resistance and PA signals, with coefficients of determination (R²) exceeding 0.9. Overall, these findings suggest that PA measurement may provide complementary information on temperature-dependent behavior that is not fully reflected in sheet-resistance measurements. Full article

Speech is a fundamental component of human communication and has become increasingly important with the widespread adoption of voice-based technologies, text messaging systems, Chatbots, and Large Language Models (LLMs). While AI systems are going through exponential breakthroughs, they often prioritize the dominant variant of a language. Using the TEDx Talks Brazilian Accents (TTBAcc) dataset, this research provides an acoustic analysis of two Brazilian Portuguese accents: Nordestino and Paulistano and an unsupervised accent clustering to find distinctive characteristics and investigate factors that can potentially support the monitoring of emerging and endangered accents. The acoustic analysis compares rhotics and vowels produced by speakers of both accents. The analysis of rhotics provided limited evidence of meaningful difference between accents. In contrast, the vowels exhibit significant differences in the fundamental frequency ($f_0$), the first and second formant frequencies ($F_1$ and $F_2$) and intensity, suggesting that these acoustic features may be more effective to distinguish between the investigated accents. For accent clustering, $f_0$, length, volume, and formant frequencies ($F_1$ and $F_2$) are used as inputs. Among the evaluated approaches, K-Means, with $K=38$ achieves the best performance, obtaining a Rand Score of 0.775 ± 0.028 and 0.524 ± 0.032 homogeneity, the best performing model. The optimal number of cluster exceeds the number of classified accents, which may indicate either an over-segmentation of data or a finer-grained phonetic variation captured in acoustic features. These findings highlight the potential of using acoustic features for investigating the variation in regional accents, and provides a basis for further research in monitoring emerging and endangered accents. Full article

Broadband, low-frequency sound absorption within a compact device remains a central unsolved problem in noise control engineering, arising from fundamental trade-offs among resonator volume, absorption bandwidth, panel thickness, and frequency tunability that no passive, linear, time-invariant system can simultaneously circumvent. This review establishes a unified mass–spring–damping (MSD) framework applied systematically across the full spectrum of resonance-based absorber technologies. From first principles, we derive the mass–stiffness coupling result (the mass-disappearing result of Shen and Liu): fixing the resonance frequency imposes $K=M{\omega }_{\mathrm{res}}^2$, so acoustic mass and stiffness cannot be adjusted independently; the half-absorption bandwidth ${\Pi }_1=\eta /\left(M{\omega }_{\mathrm{res}}\right)+V{\omega }_{\mathrm{res}}/\left(c_0{S}_{\mathrm{tar}}\right)$ then depends explicitly on the cavity volume V (system stiffness) and on the damping coefficient $\eta$, rather than on mass as an independent lever. This explains why neck extension, space-coiling, and membrane loading—which merely add mass while leaving the cavity stiffness unchanged—fail to broaden the absorption band at fixed volume, and refocuses the design effort on stiffness reduction and damping control. Five non-dimensional performance metrics are introduced that collapse the scattered literature into a single, scale-independent language for rigorous comparison across all absorber families: normalised half-absorption bandwidth ${\Pi }_1$, volume efficiency ${\Pi }_2$, integral absorption criterion ${\Pi }_3$ tied to the Rozanov causality bound, quality factor $Q=1/{\Pi }_1$, and frequency-thickness ratio ${\Pi }_4$. A two-degree-of-freedom acoustic–structural coupling model yields closed-form effective stiffness and damping, revealing how structural loss augments acoustic damping, how modal veering produces split absorption peaks, and how the anti-resonance frequency becomes a designable parameter. A critical distinction is drawn between mathematical negative stiffness (a fitting artefact) and physical negative stiffness via repulsive magnets, bistable elements, or negative-capacitance piezoelectric shunts, which genuinely reduces cavity stiffness, lowers resonance frequency, and widens bandwidth beyond the passive causality bound. The shunt electromechanical diaphragm further demonstrates $\alpha >0.9$ at nine tonal frequencies spanning three octaves without mechanical modification. Finally, embedding MSD equations and ${\Pi }_1$–${\Pi }_4$ bounds as hard physical priors in AI/LLM-assisted design frameworks is identified as the key step toward provably physically consistent absorber synthesis. Full article

Hybrid structural materials (HSMs), such as nanoparticle-treated fabrics, have been shown to enhance acoustic and ballistic performance in multifunctional protective structures. They offer a promising means for low-frequency (<~1000 Hz) noise mitigation, which remains a critical challenge in aerospace and defense applications. The measurement and modeling of their sound transmission loss (TL) behavior using a coupled acoustic–poroelastic approach is explored in this study. A colloid-based soaking and drying process is used to impregnate nanoparticles into the fabric. Previous studies using SEM imaging have established that at low (<~20 wt.%) treatment levels, the nanoparticles agglomerate in the interstitial spaces between yarn crossover points, whereas at higher levels, they begin to coat the yarn bundle tops. TL was measured experimentally using normal-incidence impedance tube tests. Further, parameters such as static flow resistivity, porosity, flexural modulus, and density required to model the neat and treat samples as fluid-filled porous solids using the Biot–Allard model were obtained from experiments for a limited set of neat and treated cases. Static flow resistivity was measured using an air permeability tester as per ISO 9237, and a modified version of the Peirce’s cantilever beam test was used to obtain the flexural modulus for neat and treated samples. Porosity was estimated using digital image analytics. The poroelastic fabric model was implemented in finite element simulations, and the predicted TL was compared with experiments including those for uncalibrated treated cases. The model shows close alignment with measured TL at low frequencies (<~600 Hz) for all cases but deviates closer towards the theoretical mass law at higher frequencies, where flanking effects and the influence of the hierarchy of pores are expected to be dominant in experiments. Further studies are underway to incorporate such higher-order effects to improve predictions at higher frequencies. The development of this model provides a means to capture the influence of nanoparticle addition on the acoustic performance of Kevlar, enabling fast and efficient virtual design iterations. The approach helps optimize HSMs for noise mitigation in multifunctional applications for the aerospace, defense, and infrastructural sectors. Full article

Digital modeling of traditional Chinese musical instruments significantly lags behind that of their Western counterparts, limiting advances in cultural preservation and related research. This paper addresses score-to-audio generation for the Chinese bamboo flute (dizi), aiming to synthesize expressive audio with human-like performance nuances directly from Musical Instrument Digital Interface (MIDI) scores. Two core challenges remain in existing score-to-audio synthesis methods: first, the scarcity of large-scale paired MIDI-audio training data for traditional Chinese instruments; second, the inability of standard MIDI to encode instrument-specific expressive techniques, such as vibrato, pitch bends, and ornamentations. To address these challenges, we propose a scalable workflow that generates large-scale synthetic MIDI-audio pairs through rule-based score randomization, automated digital audio workstation (DAW) rendering with commercial sample libraries, and standardized feature extraction. Performance technique information is directly encoded into the MIDI stream using out-of-range MIDI note numbers, achieving more effective conditioning than external control methods. Our system is built upon the Musical Instrument Digital Interface–Differentiable Digital Signal Processing (MIDI-DDSP) framework. Large-scale synthetic data is used for pre-training to establish timbral consistency, while real recordings from the University of Rochester Multi-Modal Music Performance (URMP) flute corpus are employed for fine adjustment to achieve expressive dynamic variations. Synthetic data alone yields stable but less expressive outputs, whereas real data alone risks overfitting. The combined strategy achieves a realistic timbre with controllable dynamics and performance techniques. Full article

Research on acoustic vases embedded in historical buildings has progressively developed through archaeology, architectural history, and acoustics, producing extensive documentation on their distribution, geometry, installation and possible acoustic role, with experimental evidence from in situ measurements, laboratory tests, and numerical analyses. However, documentation and measurement procedures remain highly heterogeneous, limiting reproducibility and comparative interpretation. Within this context, the present work proposes a preliminary methodological framework for future investigations. It reviews the principal European documentation, census, experimental, and numerical approaches identified by the authors. Particular attention is given to the recording system developed by Palazzo-Bertholon and Valière and to the experimental methodologies adopted in previous studies, including procedures, acoustic descriptors, and instrumentation. A possible extension of the “fiche d’information” is discussed to make geometrical, spatial, and installation-related data more explicit for comparative analyses, acoustic modelling, and measurement planning. A documented case study is used to illustrate the proposed organization of information, followed by a simplified acoustic simulation showing how structured data may support model construction and interpretation. The proposed procedure therefore combines simulation and in situ measurements, with standard and advanced investigation levels. The study is aimed at improving documentation quality, consistency, and comparability rather than providing definitive evidence of acoustic effectiveness. Full article

To investigate the evolution of acoustic emission (AE) parameters during the flexural failure of reinforced concrete (RC) beams subjected to freeze–thaw and corrosion, four RC beams were fabricated and assigned to four conditioning regimes: no deterioration, freeze–thaw only (75 cycles), corrosion only (4.8% mass loss), and combined. Three-point bending tests were conducted, combining AE and digital image correlation (DIC) techniques. The damage process was divided into four stages: micro-crack initiation, stable crack propagation, unstable crack propagation, and failure. The evolution of AE parameters including ring count, energy, amplitude, peak count, and duration was analyzed. Each parameter is positively correlated with load level and rises as the damage stage advances. The slope of cumulative parameters reflects crack development more reliably than instantaneous values. The effect of corrosion on these parameters is significantly greater than that of freeze–thaw. For corroded beams, AE parameter levels are higher during the micro-crack initiation stage but lower during the stable crack propagation stage. The overall AE activity decreases with increasing deterioration degree. High-amplitude events increase with damage progression, but fewer high-amplitude events are observed at the failure stage of severely deteriorated beams. This study reveals the correspondence between AE parameters and damage stages, providing an experimental basis for damage assessment using AE techniques. Full article

In the context of temporary urban environments such as festivals and construction sites, acoustic discomfort inside textile-based party tents remains a critical yet under-addressed issue. This study, developed in collaboration with industrial partners from the construction and textile sectors, aimed to design and assess lightweight, flexible sound-absorbing solutions capable of improving acoustic comfort while reducing environmental impact. A set of nine composite textile samples were fabricated using combinations of recycled and technical materials. Their acoustic behavior was characterized through standardized laboratory tests (ISO 10140-2 and ISO 354:2004) and full-scale prototypes under simulated real-world conditions. Simultaneously, a Life Cycle Assessment (LCA) was conducted according to ISO 14040:2006 and EN 15804:2020 standards to quantify environmental impacts from cradle to gate. The results demonstrate that it is possible to achieve an effective balance between acoustic performance and environmental sustainability. Integrating both types of assessment into the material selection process enables more informed, responsible design decisions for temporary textile structures, aligning construction practices with growing demands for functional and sustainable solutions. Full article

Wave propagation along acoustic black hole waveguides (ABH) consisting of arrays of functionally graded perforated rings (FGPR) is investigated by developing their linearized electro-acoustic analog models. These models simulate the interactions between the different components of the ABH/FGPR as influenced by the design parameters of the perforated rings and coupled acoustic cavities. The developed electric analogs consist of arrays of resistors simulating the flow resistance through the perforations, inductances to quantify the inertia of the gas moving inside these perforations, and capacitances to describe the storage behavior of the cavities between neighboring rings. The dynamic interactions between these electric components are described by a state-space model in terms of the incoming and outgoing flow velocities as well as the pressures before and after each FGPR. In this manner, it is possible to determine the spatial distributions of the flow velocities and pressures along the ABH which are necessary to demonstrate the effectiveness of the proposed ABH/FGPR in generating the ABH effect by monotonically decelerating the flow along the waveguide and bringing it to a complete stop. The predictions of the developed electro-acoustic analog models are validated against the predictions of the classical “Transfer Matrix Method (TMM)” and experimental results established by Petrover and Baz (2025). Furthermore, these predictions are also validated against the predictions of a developed MATLAB SimScape Model of the electro-acoustic analogs. The comparisons between the predicted and measured results show close agreements and validate the accuracy of the developed electro-acoustic analog models. Full article

Personal sound zones (PSZs) in cars allow occupants in different seats to enjoy distinct audio content without mutual interference. However, achieving sufficient acoustic isolation in real-world vehicle cabins remains challenging. In-vehicle experiments were conducted to enhance acoustic contrast using four headrest loudspeakers mounted on the rear-right seat to create dark zones at the front seats. Three arrangements of four headrest loudspeakers on a single seat were evaluated: longitudinal horizontal, lateral horizontal and vertical configurations. Compared with distributing four headrest loudspeakers across two seats, concentrating them on one seat yielded better acoustic contrast. When evaluated in the car using control points distributed on a horizontal plane, the vertical configuration exhibited superior performance among the tested arrangements, achieving an overall acoustic contrast of 12.4 dB over the 88–4525 Hz frequency band. This represents improvements of 3.9 dB over the two-loudspeaker setup and 0.9 dB over the two-seat-distributed four-loudspeaker arrangement. These results indicate that the vertical loudspeaker arrays on a single seat provide an effective approach for improving PSZ isolation in automotive environments. However, this enhanced acoustic isolation comes at the cost of increased array effort at low frequencies compared to the two-seat distributed configuration, as quantified in the study. Full article

Rotating machines in industrial environments often generate fundamental-frequency noise and its harmonics, which may affect workers’ physical and mental health. This study investigates the active control of single-frequency noise in an open sound field. A multi-harmonic active noise control (ANC) algorithm based on local secondary path (LSP) equalization is adopted to reduce computational complexity. A semi-anechoic chamber test platform is built to experimentally investigate the influence of the distance between the error microphone and the secondary source (Des), as well as collinear and non-collinear arrangements, on noise-reduction level, spatial attenuation range, and the upper frequency limit of noise control. The experimental results show that, under a 100 Hz tonal noise condition, the noise-reduction level first increases and then decreases as Des increases. This phenomenon can be explained by the phase relationship between the primary and secondary sound fields. As Des changes, the propagation delay of the secondary sound field also changes, thereby altering the interference pattern at the monitoring positions. When the phase difference approaches destructive interference, higher noise reduction is achieved, whereas further increases in Des gradually reduce the cancellation effectiveness because of phase mismatch. A relatively high noise-reduction performance is maintained when Des ranges from 200 cm to 500 cm. Secondary destructive interference may also appear at certain distances. In addition, the collinear arrangement shows a significantly higher upper frequency limit for noise reduction in comparison with the non-collinear arrangement. The results provide useful experimental evidence and practical guidance for optimizing the layout of ANC systems in complex acoustic environments such as vehicles and industrial plants. Full article

The empirical calibration of remote microphone probes, used to acquire unsteady pressure fluctuations in a wide range of fluid-dynamic applications, often introduces spurious resonance into the estimated frequency response, i.e., the transfer function, of the probe over the multiple steps it requires. To prevent this spurious resonance from affecting the unsteady pressure measurements, the transfer functions tend to be manually post-processed. Yet, such a procedure can constitute an additional source of uncertainty that hampers the accuracy of the results. A semi-empirical calibration method based on Bayesian inference was previously developed to tackle this problem: ASSIST (BAyesian proceSsing of SpurIous reSonance in calibraTion data). Through this technique, spurious resonance is removed and replaced with a physically correct alternative in a much less operator-reliant manner. However, its application requires a thorough understanding of the model and the related assumptions. This paper provides the knowledge required to apply ASSIST to the calibration of remote microphone probes. It covers the acquisition of the calibration data, the set-up of the method, the analysis of the results, and the iterative tuning of the input parameters to achieve the optimal fit. These steps are demonstrated on an open-source acoustic finite-element method simulation dataset, allowing the analytic line-cavity model to be compared with a 3D model and the impact of the relevant parameters constituting the method to be discussed. This framework is finally used to propose a novel development of the technique that reduces the calibration process of remote microphone probes to one single step, removing the source of the spurious resonance and enabling their in-situ calibration on non-sealing surfaces. Full article

Due to fluctuations in flow rate, pressure, and pump operating states, as well as environmental disturbances such as temperature variations and structural vibrations, pipeline leakage signals exhibit significant nonstationary characteristics. The traditional fixed sensor is limited by the layout position, resulting in suboptimal detection performance. For micro-leakage, it is even more difficult to achieve detection. With the advantages of small size and strong passing ability, the acoustic inner detector is well-suited to the task of comprehensive pipeline detection. Therefore, this paper carried out unsteady micro-leakage detection based on acoustic internal inspection signals. The unsteady micro-leakage simulation experiment of pipeline was carried out, and the leakage acoustic signal was collected for method verification. This paper investigates the integration of variational mode decomposition (VMD), random forest (RF) and least squares support vector machine (LSSVM) for signal processing and leakage classification. An unsteady micro-leakage detection method based on acoustic internal inspection signals was proposed, which is well-suited to the leakage detection task of pipelines. Experimental results indicated that the proposed method achieved a recognition accuracy of 95.31%, outperforming conventional leakage detection methods. Full article

We introduce the String Ensemble Chords Dataset (SECD), a large-scale controlled compositional audio dataset comprising 287,088 harmonic-interval and chord instances constructed through additive superposition of professionally recorded isolated string notes from the Philharmonia Orchestra into duo-, trio-, and quartet-like four-voice mixtures. Each mixture includes exact per-voice metadata for absolute pitch, dynamic marking, and playing technique, and the corpus is organised into six dataset groups covering harmonic intervals, triads, and seventh chords under loose and strict metadata-consistency conditions. To demonstrate dataset utility, we define four representative and reproducible reference benchmarks: ensemble size recognition, triad chord quality identification, per-instrument dynamics classification, and playing technique-family recognition. Baseline Audio Spectrogram Transformer (AST) models achieve test accuracies of 98.67%, 93.73%, 98.19%, and 99.39%, with corresponding macro-F1 scores of 98.64%, 93.73%, 98.01%, and 97.29%, under a complete-instance-disjoint, in-domain evaluation protocol. These results provide reproducible reference performance for the selected SECD tasks and demonstrate the corpus’s utility for controlled analysis of harmonic, timbral, dynamic, and textural attributes in classical string audio. The full SECD corpus is released through Zenodo as constructed audio mixtures with accompanying metadata, while the project GitHub repository provides the EXP1–EXP4 benchmark code, saved split definitions, and the mini-SECD demonstration package for lightweight reproducibility. Full article

To address the lack of comprehensive quality evaluation indicators for heat treatment after bilateral induction hardening of high-speed linear guide rails, this study draws on the concept of geometric tolerance to innovatively propose a quantitative evaluation indicator for the “symmetry” of the hardening layer depth profile, and conducts non-destructive evaluation research based on ultrasonic transverse wave backscattering technology. Aiming at the complex cross-sectional profile of the guide rail and the problem of anisotropic acoustic scattering, a multi-dimensional symmetry characterization framework driven jointly by “local pair-wise tolerance zone constraints” and a “global equivalent case depth metric” was established. This dual-driven evaluation framework effectively eliminates the evaluation loophole of “false symmetry” caused by the mutual cancellation of opposite positive and negative local deviations. By constructing an equivalent hardened layer model based on discrete feature point mapping, the interference of non-parallel complex curved surfaces on traditional continuous B-scan imaging is successfully circumvented, achieving stable characterization of the overall hardening layer coverage under specific process parameters. A 15 MHz water-immersed point-focusing ultrasonic transverse wave oblique incidence detection system was developed, paired with a self-designed spring-loaded passive conformal tracking clamping mechanism for continuous automated scanning. Experimental results demonstrate that the overall equivalent symmetry of the tested guide rail specimens remains above 98%. Verified by the metallographic Vickers hardness gradient method, the equivalent relative error between the ultrasonically measured case depth and the physical case depth is only 1.0% and 1.6%. This proves that this non-destructive evaluation method possesses excellent measurement accuracy and holds significant industrial value for online non-destructive monitoring. Full article

Detecting and localizing leaks in buried pipelines typically requires direct access to the pipe, which is often impractical in real-world conditions. Although ground-surface vibration measurements offer a non-intrusive alternative, their potential for spatial leak localization remains underexplored, particularly in relation to frequency-dependent attenuation effects. This study investigates how frequency-dependent energy decay encodes spatial information in leak-induced ground vibrations. Experimental wok was conducted using an outdoor buried pipeline testbed, where surface acceleration data were collected with a movable array of piezoelectric sensors. The measurements were reorganized into L-shaped sensor trios to enable directional analysis and increase the number of spatial configurations. Energy-based features extracted from discrete frequency bands were used to represent the leak signatures, capturing both attenuation behavior and soil–pipe interaction effects. Artificial Neural Network and Random Forest models were trained to estimate leak coordinates in a local reference frame. The results demonstrate high localization accuracy at the centimeter scale and reveal consistent relationships between prediction error, distance, and signal-to-noise ratio. These findings show that frequency-dependent attenuation provides a robust basis for spatial inference, and that combining ground surface vibration measurements with lightweight machine learning models offers an effective and non-intrusive solution for leak localization in buried pipelines. Full article

Posterior acoustic shadowing is a key diagnostic feature in ultrasound imaging of calcified lesions, such as gallbladder and kidney stones. However, conventional assessment relies primarily on qualitative interpretation, and its underlying structural characteristics remain insufficiently quantified. This study aimed to quantitatively characterize posterior acoustic shadows using wavelet-based texture analysis and to investigate their diagnostic relevance across different expert-defined shadow confidence groups. Ultrasound B-mode images were analyzed from gallbladder stone and kidney stone datasets. Regions of interest (ROIs) were extracted from gallbladder and kidney stone images across three shadow confidence levels (50–60%, 60–80%, and >80%), and multi-scale wavelet features were computed. The results demonstrated a substantial reduction in high-frequency components with increasing attenuation. Total detail energy decreased by approximately 80% in the gallbladder group and 55–60% in the kidney group from low to high shadow confidence levels. Similarly, normalized ratios (E_{detail/approx} and E_detail/total showed consistent decreases, with inter-group differences of approximately 2.3–2.5-fold at 50–60%, which converged to negligible levels (<2.4% difference) at >80%. These findings suggest that wavelet-based energy distributions may provide acoustically interpretable quantitative descriptors of posterior shadow formation in ultrasound stone imaging. Full article

Sound has an important role in how users perceive their environment. Under this context, a soundscape approach was followed for the evaluation of indoor spatial experience of university architecture studios. A tailored framework of factors affecting sound perception and spatial experience was proposed for this study and used in the questionnaire. An indoor soundscape questionnaire investigating architecture students’ perception of their acoustical environment and how it affects their spatial experience was designed and applied. The survey was conducted with a total of 191 first-grade and fourth-grade students. Demographic characteristics were found to be statistically associated with users’ indoor environment expectations and acoustic perception. Among many statistically significant correlations between soundscape perception and spatial experience, correlations between intelligibility perception and architectural design expectations, as well as between perception of and reaction to sound sources and perception of spatial experience factors, stood out. Full article