This work investigates the propagation of elastic waves in soil induced by a leaking buried pipe, emphasizing the influence of uncertainty on ground-surface responses. The analysis is grounded in the underlying wave physics and employs a stochastic modelling framework to capture variability in soil properties and system parameters. While previous studies have primarily focused on pipe vibrations, the present work extends the analysis to ground-surface responses, which are directly relevant to non-invasive monitoring techniques. A probabilistic model is developed to characterize the resulting ground vibrations, enabling a systematic quantification of uncertainty inherent in leak-related signals. The proposed approach employs a polynomial chaos expansion surrogate model and is validated against Monte Carlo simulations, demonstrating excellent agreement and computational efficiency. The analysis reveals the distinct contributions of shear and compressional waves and shows that their interference can cause abrupt phase changes coinciding with local minima in displacement magnitude, an effect absent when only shear waves are radiated. Additional simulations show how burial depth influences these features, confirming the robustness of the proposed framework across typical installation conditions. The proposed stochastic framework represents an important step towards enhancing the reliability and interpretability of ground-based techniques for buried pipe localization.
This study proposes a decagonal Kresling origami-based acoustic metamaterial, termed DKOAM, for tunable low-frequency sound absorption. The proposed structure uses a decagonal Kresling-folded cavity as the reconfigurable backing cavity of a Helmholtz-type resonator. It combines it with neck-impedance regulation to improve the tunable absorption bandwidth. The folded cavity height can be adjusted by reconfiguring the Kresling structure, thereby regulating the equivalent acoustic volume, cavity compliance, and impedance-matching condition. A conventional transfer-matrix formulation is employed as an analytical tool to describe the geometric–acoustic coupling among the folded cavity height, equivalent acoustic volume, perforation ratio, neck impedance, input impedance, and absorption coefficient. Finite element simulations and impedance-tube measurements are conducted at representative folded-cavity heights to validate the theoretical prediction. By combining prototype validation with numerical design-window analysis of the multi-aperture configuration, the effective absorption response (α > 0.8) can cover 166–708 Hz. The single-hole configuration provides an effective absorption range of 166–315 Hz, while the multi-hole configuration extends the effective absorption range to 305–708 Hz through distributed neck impedance and improved impedance matching; at the lowest-frequency state, the sample thickness is only approximately 1/49 λ. These results indicate that the proposed DKOAM provides a feasible structural strategy for tunable low-frequency sound absorption via decagonal Kresling-folded-cavity reconfiguration and multi-aperture neck-impedance regulation.
In this work, composite porous panels incorporating coir pith particles are developed as sustainable acoustic materials for building acoustic applications, using raw graded coir pith particles and a cement binder fabricated through a simple mixing and pressing technology. The resulting composites exhibit favorable porosity for acoustic treatment, and by adjusting the coir pith mixture proportion, their acoustic behavior can be progressively tuned. Several specimens are fabricated with varying coir pith-to-cement volume ratio from 10 to 60
Humpback whales (Megaptera novaeangliae) undertake long-distance annual migrations to access seasonally optimal habitats for feeding and reproduction. However, shifts in migration timing have been documented across multiple populations worldwide. Under rapid environmental change and increasing coastal development, there is growing concern that long-distance migrants may arrive in critical habitats outside favourable ecological windows. Along Australia’s east coast, the E1 subpopulation migrates between Antarctic feeding grounds and Coral Sea breeding areas, yet substantial geographic gaps remain in monitoring their occurrence, particularly along their migration route. To address this, a passive acoustic recorder was deployed throughout the migratory period in Batemans Bay, NSW from May to September 2024. Across 102,960 min of acoustic monitoring, humpback whale vocalisations were detected in 70
Conventional noise control strategies that rely primarily on reducing acoustic energy often face practical limitations in real-world environments. The audio injection method (AIM) offers an alternative, sound quality-oriented approach by superimposing controllable, positive sounds to mitigate annoyance. Because the superimposed sound is perceptually more complex than the original noise alone, annoyance under AIM is expected to be shaped not only by acoustic exposure but also by non-acoustic factors. Consistent with the growing emphasis on such factors in ISO/TS 16755-1:2025, this study investigates the key non-acoustic factors of short-term annoyance for superimposed sounds in AIM contexts. A quasi-field online questionnaire survey was conducted, recruiting 304 participants. Potential components related to non-acoustic factors were identified and refined using exploratory factor analysis (EFA), and a path-based structural model was then used to quantify direct and indirect effects on annoyance. The results show that: (1) AIM can effectively reduce reported annoyance across multiple noise scenarios; (2) noise sensitivity adversely influences attitudes toward the original noise source, thereby increasing original noise annoyance; (3) original noise annoyance significantly predicts annoyance of the superimposed sound; and (4) more than half of participants expressed acceptance of AIM, and positive attitudes toward AIM together with preference for controllable sounds are associated with lower superimposed-sound annoyance. These findings provide a mechanism-based, interpretable framework for incorporating non-acoustic factors into the design and evaluation of AIM-type interventions in environmental and architectural acoustics.
This paper studies the vibro-acoustic response and control strategies of composite laminated stiffened plate-shell and acoustic cavity coupled systems based on the improved Fourier series method (IFSM) and the Rayleigh–Ritz method. A vibro-acoustic control model of a closed cylindrical stiffened shell, a stiffened radiating plate, composite laminated curved beams, and internal acoustic cavities for the coupled system is established. According to first-order shear deformation theory (FSDT), the displacement admissible function of the substructures and the sound pressure admissible function of the acoustic cavity are established based on IFSM. The Lagrange energy equation of the coupled system is developed to solve the vibro-acoustic characteristics according to the Rayleigh–Ritz method. The accuracy of this method can be demonstrated. Based on this, the vibro-acoustic response under multi-source excitation is analyzed. The effect of secondary sound or force sources on structural vibration or the sound field within an enclosed acoustic cavity was analyzed. Finally, the selection strategy for the secondary excitation under four different control targets is discussed in a unified numerical example. There are optimal noise reduction ranges when the secondary source amplitude is around 1 kg/m2. To achieve the control targets of reducing all four targets by 8 dB, the secondary sound excitation distance should be 0.43–0.54 m and 0.67–0.73 m, and its amplitude ratio to the primary excitation should be 0.85–1.11. This provides a theoretical foundation for low-noise design of plate-shell structures.
The common brushtail possum is a major invasive species in New Zealand, damaging native ecosystems and agricultural systems and is a target of the national Predator Free 2050 eradication programme. Reliable, low-cost monitoring is critical to this programme, and acoustic detection offers a scalable alternative to traditional trapping and camera-based methods. The bioacoustics approach to automated brushtail possum detection using deep learning models suffers from excessive false alarms. At the same time, the high computational demands of the most accurate models make them unsuitable for resource-limited edge devices. In this paper, a targeted hard-negative mining method, Cross-Model Confusion Mapping (CMCM), is proposed to overcome these problems. It uses the error profile of a pre-trained model to identify bird calls most frequently misclassified as possum vocalisations. These bird calls are then relabelled and added to the training data. Three CMCM audiosets were generated and compared with size-matched sets assembled through untargeted sampling. CNNs with 3, 5, 7, 10, and 13 layers were trained using identical augmentation pipelines. Experiments showed that CMCM-trained models maintain accuracy while significantly reducing false alarms. In particular, the 10-layer CMCM-trained CNN achieved the most reliable detection with zero false positives. The inference times are orders of magnitude faster, with substantially lower computational demand, than the state-of-the-art Audio Spectrogram Transformer. These findings suggest that CMCM enables accurate, low-latency possum detection suitable for real-time deployment on edge devices. The method is generalisable to other bioacoustic detection tasks where false positives arise from acoustically similar non-target species.
In this paper, we propose an innovative design for dual-conical mufflers with enhanced sound transmission loss (STL) using triply periodic minimal surface (TPMS) metamaterials. The muffler improves STL at low and mid-frequencies, where conventional mufflers are least effective. The design leverages TPMS structures’ unique attributes, such as porosity, high surface-area-to-volume ratio, and the ability to tune acoustic impedance to modify wave propagation through the muffler. Three TPMS structure types are considered: P-type, G-type, and IWP-type, which exhibit different configurations and resonances. The designs are assessed in the frequency domain from the numerical modeling software COMSOL Multiphysics® using a high-fidelity 3D model to analyze STL, sound pressure level (SPL), and peak acoustic pressure distributions using post-processed simulation data obtained from COMSOL Multiphysics. An experimental prototype was also fabricated using 3D printing and validated through impedance tube measurements, confirming the accuracy of the results. Comparison between numerical and experimental results shows good agreement and is acceptably robust. Overall, the results indicate that mufflers with TPMS topology outperform their metamaterial-free cylindrical and conical counterparts of equivalent mass. Moreover, the G-type designed muffler achieved the best overall STL, given the structure's periodic complexity and localized resonances relative to the other TPMS geometries. The IWP-type structure exhibits a pronounced high-frequency STL drop due to structural symmetry and wave-guiding effects. Collectively, these results demonstrate the feasibility of geometry-driven acoustic metamaterials for passive noise control. The results indicate the potential of TPMS-based geometries for enhancing STL in compact muffler configurations. However, further investigations considering mean flow, thermoviscous losses, and high-temperature operating conditions are required before practical exhaust applications can be fully assessed.
Psychoacoustic metrics (PMs) are quantitative representations of auditory perception that commonly include loudness, sharpness, roughness, fluctuation strength, and tonality. Unlike traditional physical quantities (such as sound pressure level), they reflect the complex nonlinear relationship between acoustic signals and auditory perception to a greater extent. Algorithms for PMs have been developed and integrated into computational tools, but discrepancies exist in results from different tools, and no systematic evaluation has been conducted to date. Four tools were used to calculate PMs for both standard and measured sound stimuli. The accuracy of results from different tools was verified using standard stimuli, and differences in results for measured samples were analyzed using two evaluation methods: statistical test method and perceptual difference method. The impact of these differences was assessed through sound quality evaluation tasks. The perceptual difference method complements statistical tests. The joint deviation in loudness and modulation metrics (fluctuation strength and roughness) can inflate the annoyance discrepancy to 8.8 points on an 11-point rating scale. End-to-end sound quality models avoid prediction accuracy drops due to PM calculation discrepancies. Discrepancies in PM calculations across tools significantly affect annoyance ratings and prediction accuracy. The perceptual difference method can be used as a complement to statistical analysis, and end-to-end models offer robustness against calculation discrepancies.
Identifying temporal patterns in song production can provide insight into behavioural ecology of baleen whales, such as reproduction, foraging, and migration. Off northwest Australia, Omura’s whales produce rhythmically repeated two-unit doublet and one-unit singlet vocalisations, characteristic of baleen whale song. This study utilised four multi-year passive acoustic recording sites to analyse the distribution of the Omura’s whale along the northwest coast of Australia and investigate diel, lunar, and seasonal patterns in the species song. Seasonality of doublet and singlet production was compared in the Timor Sea, with doublets accounting for over 98
Helmholtz resonance provides a well-established acoustic basis for determining volume via the resonance-frequency–volume relationship. However, frequency-tracking methods are typically too slow for dynamic measurements. We present an alternative physical model, the sound-pressure quality-factor (SPQF) model, which estimates volume in real time from cavity sound-pressure amplitude, avoiding frequency hunting. The model follows from the equations governing the driven, underdamped vibration of the port-air mass. The resonator is excited at its empty-cavity natural frequency with a single-tone drive; inserting a sample reduces the steady-state pressure amplitude, from which displaced volume is inferred. We validate the method with liquid and solid samples in 1-, 2-, and 3-L cavities and in a mechanically adjustable chamber under dynamic conditions. The approach achieved millilitre-level accuracy for solids and relative expanded uncertainty U, k = 2 < 0.1
This paper presents an innovative scheme for layout optimization of bi-material structures, which can be effectively applied to the design of the structural–acoustic coupled systems subjected to mid-frequency excitation. The basic theory of the scheme is the statistical modal energy distribution analysis (SmEdA). As an improved and extended version from statistical energy analysis (SEA), the core concept of computing energy transfer at the per-mode level enables the SmEdA to address mid-frequency vibration problems. The proposed optimization model aims at minimizing the acoustic energy in the cavity through rational bi-material distribution (stiffer material and softer material), subject to a weight constraint on the stiffer material. The virtual density of the structural plate, obtained by the solid isotropic material with penalization (SIMP) method within the bi-material interpolation model, serves as the design variable. A volume-preserving Heaviside penalization is incorporated into the optimization framework for eliminating the intermediate density region. Moreover, sensitivity analysis is conducted using the complex variable method (CVM) to enhance the computational accuracy and practical applicability of the established optimization framework. Finally, numerical cases are presented to elaborate the practicality of the developed optimization scheme. It can be concluded that: (a) A considerable reduction of the overall acoustic energy within the cavity is observed; (b) the peak value of modal coupling strength is effectively reduced and the corresponding distribution tends toward more homogenization.
In recent years, there has been a surge focusing on advanced sound source localization methods based on deep learning. However, the black-box feature extraction mechanism impedes their optimization. This study proposes a two-step grid-free method for locating multiple sources based on deep ensemble learning and interpretable artificial intelligence (AI). In the first step, sound pressure signals received by a spherical microphone array are preprocessed into auto-power spectra, which are then fed into a classifier to count the sources. In the second step, the aforementioned signals are converted into generalized cross-correlations with phase transform (GCC-PHAT), which are then input to an ensemble regressor comprising four types of regressors for source localization. Additionally, two interpretable AI techniques, t-distributed stochastic neighbor embedding and activation maps, are employed to analyze the underlying principles of the deep learning-based method. The classifier achieves a testing accuracy of 94.59
Acoustic communication in anurans exhibits considerable plasticity, yet the role of nonlinear phenomena (NLP) and their environmental modulation remain poorly understood. We investigated the acoustic structure of advertisement and aggressive calls in a free-toed frog from Sinaloa, Mexico. Calls from 24 males were recorded under natural conditions and during playback experiments to test whether vocalizations change in response to conspecific acoustic stimulation, with particular emphasis on NLP. Differences between spontaneous and post-stimulus calls revealed strong contextual modulation, after which relationships between acoustic variables, body size, and ambient temperature were evaluated. Advertisement and aggressive calls differed significantly in temporal and spectral characteristics, with aggressive calls showing greater duration, lower dominant frequency, and increased structural complexity. Dominant frequency in advertisement calls was negatively correlated with body size. NLP were common in both call types; however, aggressive calls showed lower proportion of chaos and shorter frequency jumps. In advertisement calls, several nonlinear components were significantly associated with temperature: chaos, subharmonics, and frequency jumps decreased with increasing temperature, whereas the proportion of harmonics increased. In contrast, aggressive calls did not exhibit significant thermal relationships. This study provides evidence that environmental temperature modulates multiple nonlinear acoustic components in anuran vocalizations. Our findings highlight the bioacoustics flexibility of Eleutherodactylus interorbitalis and suggest that NLP may serve as sensitive indicators of physiological and environmental conditions, contributing to a broader understanding of spectral encoding in amphibian communication.
This study proposes a new sound absorbing panel designed for broadband low-frequency performance. The panel integrates a fixed low perforation rate micro-perforated panels (MPPs) with space-coiling and Helmholtz resonator slit-type structures, forming single- and double-layer units capable of wideband absorption. A hybrid series–parallel configuration, investigated using finite element analysis (FEA), creates multiple resonance peaks and enhances absorption bandwidth across low, mid, and high frequencies. To get optimum efficiency, a genetic algorithm (GA) is employed to optimize key geometric parameters. Experimental tests are conducted on both unoptimized and optimized prototypes, each with a 41 mm air cavity. The unoptimized design provides an absorption bandwidth of 1250 Hz (350–1600 Hz), while the optimized panel extends this slightly to 1255 Hz (345–1600 Hz). The Impedance tube measurements were validated against numerical predictions and, with the optimum design having a bandwidth-to-thickness ratio of 30.60 and being excellent performance than current absorbers documented in the literature. The proposed sound absorbing panel is thin and lightweight, making it particularly suitable for applications where weight and space constraints are critical, such as aerospace, civil engineering, and transportation, while providing a compact and practically feasible solution for broadband passive noise control.
To address the challenge of low-frequency broadband noise control in high-voltage equipment, this study proposes a composite sound-absorbing structure integrating an acoustic black hole (ABH) and multi-layer micro-perforated plates (MPPs). Its core innovations lie in the design of a power-law decreasing perforation rate and the development of a corresponding theoretical model. Methodologically, a theoretical model and design method for this composite structure were established based on the ABH mechanism. Subsequently, finite element simulations were conducted to analyze the influence of MPPs parameters on sound absorption performance and identify optimal structural parameters. Finally, specimens were fabricated via three-dimensional (3D) printing, and impedance tube tests were carried out for performance validation. The results indicate that, with a total thickness not exceeding 100 mm, the composite structure exhibits effective low-frequency broadband sound absorption within the measured frequency band of 195 1000 Hz, achieving an average sound absorption coefficient of 0.7. This performance stems from the synergistic effect between the slow-wave effect of sound waves within the structure and optimized acoustic impedance matching. The proposed structure shows significant potential for engineering applications in space-constrained scenarios and provides a new approach for noise control in high-voltage equipment.
Hybrid vehicle interior noise is mainly a hybrid noise consisting of a broadband road noise component and a narrowband order frequency noise component. Multi-channel hybrid active noise control (MCHANC) systems are considered an effective solution. However, the conventional MCHANC system still has two difficulties in solving the interior hybrid noise. The first is that increasing the number of channels not only leads to a sharp rise in algorithmic computational complexity but also demands higher system control robustness. The second is that the traditional HANC algorithm cannot sufficiently resolve the coupled interference between broadband and narrowband noise signals, resulting in limited suppression capability for unsteady-state noise. To solve the above problems, this study proposes a novel multi-channel HANC-DWT-NREC algorithm. To reduce the computational complexity of the MCHANC system, the proposed HANC-DWT-NREC algorithm contains a broadband active noise control (BANC) subsystem based on a delayless subband algorithm structure for attenuating the broadband noise components, while enhancing system robustness through subband signal decomposition. A discrete wavelet transform optimised narrowband residual error signal cancellation (DWT-NREC) subsystem is introduced to eliminate the potential narrowband residual error signals in the BANC subsystem and to avoid the coupled interference of broadband and narrowband noise signals. In addition, to dynamically balance the steady-state error and convergence speed of the system, a step-size self-adjustment strategy is proposed to adjust the step size of the BANC subsystem by constructing a convergence evaluation function. Numerous simulations and real-vehicle test experiments are carried out under different operating conditions using a headrest system. Results demonstrate that the proposed multi-channel HANC-DWT-NREC algorithm outperforms other HANC algorithms, exhibiting superior noise reduction performance and robustness under both steady-state and unsteady-state noise conditions, while achieving equalised noise reduction at both ear positions.
The sound of waterfalls is vital in shaping the soundscape of public leisure spaces, such as urban parks. This study explores the perception patterns of small-scale, single-stage waterfall sounds. Using a laboratory waterfall apparatus, sound samples were collected and analyzed under various conditions. Integrating subjective evaluations allowed us to examine the relationships between waterfall parameters, psychoacoustic metrics, and perceptual responses. Recommendations for achieving favorable waterfall sounds are provided. The results show that drop height, flow rate, and impact material significantly influence the acoustic characteristics of waterfall sounds. Generally, greater drop height and flow rate lead to increased loudness and sharpness of the sound produced by waterfall, while resulting in only minor and irregular variations in roughness. When the flow rate is low, waterfalls impacting water produce greater loudness and roughness than those impacting other materials. At high flow rates, impact with gravel produces a higher sharpness. Subjective evaluations are most strongly influenced by loudness, followed by sharpness, and then roughness. Higher loudness or sharpness leads to more negative ratings, while greater roughness results in more positive ratings. To achieve an aesthetically pleasing waterfall sound, it is recommended to prioritize water as the impact material, followed by monolithic stone, and that gravel is avoided. When using water or gravel as the impact material, a low flow rate is advisable. When monolithic stone is used, a low flow rate is recommended for high drop heights and a high flow rate for low drop heights. This study provides theoretical support for designing of waterfall soundscapes in urban spaces, offering practical solutions for improving urban acoustic quality and enhancing residents’ living experience.
This research investigates alternative methods for predicting sound transmission loss of duct liners and re-evaluates noise attenuation performance. A theoretical model based on mass-spring-damping parameters is used to analyze the transmission loss of Helmholtz resonators in ducts. The research compares analytical predictions with numerical simulations for both single and twin Helmholtz resonator configurations, examining the impact of resonator geometry, damping characteristics, and inter-resonator spacing. The ‘reactance-to-resistance’ effect is proposed to occur between resonators when placed in parallel. The results indicate that damping in a Helmholtz resonator can be used to achieve a balance between reflection and absorption effects. Resonator spacing influences system mass modification, revealing wavelength-related cyclic patterns. In addition, noncompact liner width and damping determine transmission loss performance across different frequency ranges. This research provides insights for improved duct liner design considering sound source effects and offers a deeper physical understanding of acoustic performance beyond traditional transmission loss metrics.
Research on natural materials as alternative sound absorbers for buildings continues. This paper presents a natural sound absorber composed of multi-layer coir and kenaf fibers. Normal and random incidence sound absorption measurements were conducted to evaluate the sound absorption performance. The results indicate that adding a thin kenaf fiber layer significantly enhances the sound absorption of the coir fiber. This improvement is observed in the low to mid-frequency range when the kenaf layer, with a smaller thickness than the coir fiber layer, is positioned at the outermost layer. If the kenaf layer is adjacent to a rigid surface, the improvement is predominantly in the mid to high-frequency range. However, if the thickness of the kenaf layer exceeds that of the coir layer, the experiment and Miki’s model demonstrate that the sound absorption coefficient remains nearly identical at mid to high frequency regardless of the arrangement of the layers.
