Acoustics

The sonoscape of a small town at the foot of the Northern Apennines Mountains in north–central Italy was studied using a regular grid of automatic recording devices, which collected ambient sounds during the spring of 2024. The study area is characterized by high landscape heterogeneity, a result of widespread suburban agricultural abandonment and urban development. Sonic data were analyzed using the Sonic Heterogeneity Index and nine derivative metrics. The sonic signatures from 26 stations exhibited distinct, spatially explicit patterns that were hypothesized to be related to a set of 11 landcover types and seven landscape metrics. The unique sound profile of each sample site was consistent with the emerging heterogeneity of landcover typical of many Mediterranean regions. Some sonic indices exhibited stronger correlations with landscape metrics than others. In particular, the Effective Number of Frequency Bins Ratio (ENFBr) and Sheldon’s Evenness (E) proved particularly effective at revealing the link between sonic processes and landscape patterns. The sonoscape and landscape displayed correlations significantly aligned with their variability, highlighting the ecological heterogeneity of the sonic and physical domains in the study area. This case study underscores the importance of selecting appropriate metrics to describe complex ecological processes, such as the relationships and cause-and-effect dynamics of environmental sounds among human altered landscapes. Full article

The inspection of corrosion and pitting-type defects is critical in the petrochemical, marine, and offshore industries. Guided wave inspection is widely used to detect these flaws and control operational costs. Higher order modes cluster (HOMC) guided waves, composed of higher-order Lamb wave modes, offer enhanced resolution compared to low-frequency guided waves. They exhibit minimal dispersion, reduced sensitivity to surface features such as T-joints, and retain most of their energy upon interacting with surface defects. This study employs two-dimensional finite element simulations to investigate the propagation and interaction of HOMC guided waves with defects in a T-joint and an aluminum plate. Both conventional fitting methods and machine learning (ML) models are used to estimate the depth of sharp defects reaching up to half the plate thickness. The results demonstrate that both approaches can utilize data from defects of one width to predict the depth of defects with a different width. The ML model outperforms the fitting method, achieving higher prediction accuracy while reducing dependence on expert knowledge. The developed method shows strong potential for characterizing sharp defects of varying widths, closely resembling real-world pitting corrosion scenarios. Full article

Impact sound, particularly prevalent indoors, emerges as a major source of annoyance necessitating a deeper and more comprehensive understanding of its implications. This literature review provides a systematic overview of recent research developments in the study of impact sound annoyance, focusing on advances in the assessment of impact sound perception through laboratory listening testing and standardization efforts. This review provides a detailed summary of the listening setup, assessment procedure and key findings of each study. The studied correlations between SNQs and annoyance ratings are summarized and key research challenges are highlighted. Among the studies, considerable research effort has focused on the assessment of walking impact sound and the use of spectrum adaptation terms, albeit with inconsistent outcomes. Comparison with the previous literature also shows the influence of spatial and temporal characteristics of impact sound sources on perceived annoyance, with higher spatial fidelity leading to higher annoyance ratings. Furthermore, it has been shown that the consideration of non-acoustic factors such as noise sensitivity and visual features are important for the assessment. This review provides a comprehensive overview of recent advances in the understanding and assessment of impact sound annoyance and provides information for future research directions and standardization efforts. Full article

This paper presents a comprehensive evaluation using a Z-test to assess the effectiveness of an adaptive Least Mean Squares (LMS) filter driven by the Steepest Descent Method (SDM). The study utilizes a male voice recording, captured in a controlled studio environment, to which persistent Gaussian noise was intentionally introduced, simulating real-world interference. All signal processing methods were implemented accordingly in MATLAB.version: 9.13.0 (R2022b), Natick, MA, USA: The MathWorks Inc.; 2022. The adaptive filter demonstrated a significant improvement of 20 dB in Signal-to-Noise Ratio (SNR) following the initial optimization of the filter parameter $\mu$. To further assess the LMS filter’s performance, an empirical experiment was conducted with 30 young adults, aged between 20 and 30 years, who were tasked with qualitatively distinguishing between the clean and noise-corrupted signals (blind test). The quantitative analysis and statistical evaluation of the participants’ responses revealed that a significant majority, specifically 80%, were able to reliably identify the noise-affected and filtered signals. This outcome highlights the LMS filter’s potential—despite the slow convergence of the SDM—for enhancing signal clarity in noise-contaminated environments, thus validating its practical application in speech processing and noise reduction. Full article

The aim of this article is the development of a new artificial intelligence (AI) system for the condition assessment of concrete structures. To study the process of concrete degradation, the so-called spatiotemporal waveform profiles were obtained, which are sets of ultrasonic signals acquired by stepwise surface profiling of the concrete surface. The recorded signals at three frequencies, 50, 100 and 200 kHz, were analyzed and informative areas of the signals were identified. The type of the created neural network is a multilayer perceptron. Stochastic gradient descent was chosen as the learning algorithm. Measurement datasets (test, training and validation) were created to determine two factors of interest—the degree of material degradation (three gradations of material weakening) and the thickness (depth) of the degraded layer varied gradually from 3 to 40 mm from the surface. This article proves that the training datasets were sufficient to obtain acceptable results. The built networks correctly predicted the degree of degradation for all elements of the test dataset. The relative error in prediction of a thickness of degraded layer did not exceed 3% in the case of a thickness of 25 mm. It is shown that the results for the Fourier amplitude spectra are significantly worse than the results of neural networks built based on information about the measured signals themselves. Full article

This study explores the impact of road transport on the environment, focusing on noise pollution. Using high-resolution, one-minute data from a low-cost environmental sensor, this research examines traffic flow dynamics, meteorological influences, and their relationship to noise along a major transport corridor. The methodology combines cluster analysis and descriptive statistics to evaluate the effects of deploying a Smart Motorway Variable Speed Limit (SMVSL) system over a six-month monitoring period. Results indicate that SMVSL systems not only smooth traffic flow but also significantly reduce noise variability, particularly during peak hours, thus mitigating noise peaks associated with adverse health outcomes. LAeq values were found to differ modestly between day and night, with clustering revealing a reduction in extreme noise events (LAmax > 70 dB(A)) in SMVSL scenarios dominated by heavy goods vehicles. This study further identifies associations between unmanaged speed regimes and elevated noise levels, enriching our understanding of the environmental impacts of unregulated traffic conditions. These findings inform sustainable planning and policy strategies aimed at improving urban environmental quality and enhancing public health outcomes. Full article

The aim of this study is to examine the behavior of subharmonics in a one-dimensional cavity filled with a bubbly liquid, leveraging the nonlinear softening phenomenon of the medium at high amplitudes to enhance subharmonic generation. To this purpose, we use a numerical model developed previously that solves a coupled differential system formed by the wave equation and a Taylor-expanded Rayleigh–Plesset equation. This system describes the nonlinear mutual interaction between ultrasound and bubble vibrations. We carry out several different simulations to measure the response of the subharmonic component $f/2$ and the acoustic source frequency signal f when the cavity is excited over a range around the linear resonance frequency of the cavity (the resonance value obtained at low pressure amplitudes). Different source amplitudes in three different kinds of medium are used. Our results reveal several new characteristics of subharmonics as follows: their generation is predominant compared to the source frequency; their generation is affected by the softening of the bubbly medium when acoustic pressure amplitudes are raised; this specific behavior is solely an acoustically-related phenomenon; their behavior may indicate that the bubbly liquid medium is undergoing a softening process. Full article

In this research, a global assessment of the acoustic situation of the Juan Ramón Jiménez University Hospital (Huelva, Spain) was carried out. For this study, measurements were made in situ, both outside and inside the buildings. With the methodology used, long-term exterior and interior measurements were performed, and an acoustic propagation model of exterior environmental noise was also developed, digitising the main sources of noise, thereby obtaining the corresponding noise maps of the study area. This study demonstrates that the indices of the external and internal acoustic environment of the hospital exceed those recommended by the World Health Organization, United States Environmental Protection Agency, and Spanish law itself. It is concluded that the acoustic environments, both outside and inside, should be improved, for which a series of interventions on the external zone, other interventions on the internal zone, and others on management has been proposed. Full article

This study investigates the acoustic characteristics of the alto saxophone by analyzing the spectral content of sound pressure along its bore and examining the influence of register valves. A detailed in situ analysis is presented of internal sound pressure from the mouthpiece to the bell for notes ranging from D₃ to C#₅, using a thin probe microphone needle in the neck and a movable miniature microphone in the body of the saxophone. The findings reveal that the cut-off frequency for lower notes in the first register is located near the third mode, whereas for higher notes, it shifts closer to the fourth mode. This research investigated previous assumptions that the cut-off frequency lies near the sixth mode, instead demonstrating that it occurs at lower modes depending on the note played. In the second register, the cut-off frequency consistently aligns with the second mode for all notes. The results demonstrate that opening the register tone holes alters the sound pressure level (SPL) distribution and shifts the positions of sound pressure valleys, with the first register valve having a more pronounced effect on SPL and mode shape than the second register valve. For the fourth mode in the first register, the register valves exhibit a stronger influence on SPL distribution compared to mode 2. Full article

The use of multipoles, otherwise called spherical wavefunctions, has been explored for acoustic fields that can be omnidirectional, for example, in scattering theory. Less developed is the use of spherical harmonic multipoles for the construction of directed beams, such as the Gaussian unfocused beampattern, which is an important reference beam in many practical applications. We develop the straightforward construction of a Gaussian unfocused beam using the special properties of the sum of spherical harmonics; these include the use of an imaginary offset in directing the forward propagation to the desired beampattern. Examples are given for narrowband and broadband pulse propagation in the ultrasound MHz range, with comparisons against a classical acoustics formulation of the Gaussian beam. The use of spherical harmonics forms an alternative framework for devising beampatterns, with apodization and concentration issues of the beam linked to an array of a limited number of discrete multipoles at the source. Full article

This study explores the relationship between formant frequencies and the directivity patterns of the Greek singing voice. Recordings were conducted in a controlled acoustic environment with four professional singers, two trained in classical music and two in Byzantine chant. Using microphones placed symmetrically on a hemispherical structure, participants sang the Greek vowels across different registers. Directivity patterns were analyzed in third-octave bands centered on each singer’s first three formant frequencies (F1, F2, F3). The results indicate that directivity patterns vary with register and center frequency, with differences observed across vowels and singers. These findings contribute to vocal production research and the development of simulation, auralization, and virtual reality applications for speech and music. Full article

It is often required to control the acoustic transmission across layered structures in order to favor or, more frequently, limit it in prescribed energy ranges. The selection of the materials and layer thicknesses needed to achieve a given objective is not straightforward, and it is often performed empirically. This is connected with the lack of simple models that dictate the frequency behavior of the layered structure. In this work, we present an approach to the systematic design of layered media, based on an assumption that allows us to obtain simple analytical expressions for the occurrence of bandgaps in the frequency response of ideally infinite periodic structures. Correspondingly low-transmission frequency ranges are then analyzed and discussed in finite-thickness realizations of the designed periodic structures. Full article

To make guitars with high sonic quality, it is essential to understand the relationship between the physical characteristics of the selected materials and the acoustic characteristics of the final instrument and how they will be perceived. The selection of wood for the soundboard is a crucial step in the guitar-making process. One relevant physical characteristic is internal material damping, about which, however, only little is known in comparison to other characteristics such as density and Young’s modulus. The present study investigated the relationship of soundboard damping to both physical and perceptual aspects of guitar sound. Three similar steel-string guitars were built with the damping of their soundboards varying between low, mid and high. Measurements of the transfer function and the plucked tone decay of the final guitars were carried out. A listening test and a playing test were conducted. The participants were asked to rate preference and seven sound attributes comprising loudness and both spectral and temporal aspects. To prepare the listening test, a short sequence was recorded by a professional guitarist with each guitar. The results suggest that varying soundboard damping had no practically relevant influence on the physical and perceptual aspects of the sound of the guitar used in this study. Full article

The lightweight development trend of modern residential structures reduces sound attenuation in buildings and makes sound propagation paths more complex. Neighbor-induced impact sound has become a significant source of residents’ dissatisfaction with the acoustic environment. To gain a deeper understanding of the characteristics of residential impact sound, reduce its impact on users, and improve the quality of residential buildings, a systematic review of existing research based on PRISMA2020 was carried out. Articles indexed in the Web of Science core dataset and Scopus were searched, with a cutoff date of October 2024. After screening and reviewing, 132 articles were systematically analyzed, categorizing the research on floor impact sound into four aspects, namely impact sound sources, evaluation indicators, prediction methods, and improvement measures. The results show that due to the diversity of real sound sources and differences in living habits, the standard impact sound sources in different countries or regions still need further study. Both subjective and objective evaluations indicate that heavyweight impact sound, particularly low-frequency sound, has the greatest impact on occupants and is the most difficult to eliminate. The physical characteristics of floor impact sound can be predicted using methods such as finite element analysis. However, there are fewer prediction methods for subjective evaluations due to the poor correlation between subjective and objective evaluation indicators. Though different soundproofing measures significantly improve the sound insulation of impact sound, they are still not widely applied due to materials, construction techniques, and time and economic costs. This study provides a reference for research on residential impact sound in China and offers an outlook for future research directions. Full article

The acoustic emissions of ventilation systems and their subcomponents contribute to the perceived overall comfort in indoor environments and are, therefore, the subject of research. In contrast to fans, there is little research on the aeroacoustic properties of air diffusers (often referred to as outlets). This study investigates a commercially available ceiling swirl diffuser. Using a hybrid approach, a detailed three-dimensional large-eddy simulation is coupled with a perturbed wave equation to capture the aeroacoustic processes within the diffuser. The flow model is validated for the investigated operating point of 470 m³/h using laser-optical and acoustic measurements. To identify the noise sources, the acoustic pressure is sampled with various receivers and on cut sections to evaluate the cross-power spectral density, and the sound-pressure level distribution on cut sections is evaluated. It is found that the plenum attenuates the noise near its acoustic eigenmodes and thus dominates other noise sources by several orders of magnitude. By implementing the plenum walls as sound-absorbing, the overall sound-pressure level is predicted to decrease by nearly 10 dB/Hz. Other relevant geometric features are the mounting beam and the guide elements, which are responsible for flow-borne noise emissions near 698 Hz and 2699 Hz, respectively. Full article

Beamforming for rotating sound source localization (denoted by rotating beamforming) is widely used in engineering nowadays. Acoustic shielding, such as shafts and covers, is typically employed in the practical measurement of rotating source localization. Acoustic shielding blocks the signal propagation between rotating sources and the array, and thus affects the performance of rotating beamforming. However, the detailed effects of acoustic shielding on rotating beamforming are still unclear. In this study, the blocking rate that represents the degree of signal propagation path blockage is defined first. The effects of acoustic shielding on rotating beamforming are then investigated in simulations. Finally, these effects are verified by experiments. According to the results of the simulation and experiments, rotating beamforming can still localize rotating sources, as long as the signal propagation path is not completely blocked. However acoustic shielding decreases sound intensity accuracy, especially when the blocking rate is larger than 50%. When acoustic shielding is employed, the ability of rotating beamforming to compensate for Doppler effects weakens. Full article

Traffic safety experiments are often conducted in virtual environments in order to avoid dangerous situations and conduct the experiments more cost-efficiently. This means that attention must be paid to the fidelity of the traffic scenario reproduction, because the pedestrians’ judgments have to be close to reality. To understand behavior in relation to the prevailing audio rendering systems better, a listening test was conducted which focused on perceptual differences between simulation and playback methods. Six vehicle driving-by-scenes were presented using two different simulation methods and three different playback methods, and binaural recordings from the test track acquired during the recordings of the vehicle sound sources for the simulation were additionally incorporated. Each vehicle driving-by-scene was characterized by different vehicle types and different speeds. Participants rated six attributes of the perceptual dimensions: “timbral balance”, “naturalness”, “room-related”, “source localization”, “loudness” and “speed perception”. While the ratings showed a high degree of similarity among the ratings of the sound attributes in the different reproduction systems, there were minor differences in the speed and loudness estimations and the different perceptions of brightness stood out. A comparison of the loudness ratings in the scenes featuring electric and combustion-engine vehicles highlights the issue of reduced detection abilities with regard to the former. Full article

Aims: The aim was to assess the agreement between microphone-derived and neck accelerometer-derived voice acoustic parameters and their associations with recording moments and speech types. Methods: Using simultaneous recordings, a 7-week study on a single individual was conducted to reduce intersubject variability. Agreement was assessed using Bland–Altman plots, and associations were examined with generalized estimating equations. Results: Bland–Altman plots showed no significant bias between microphone (MIC) and accelerometer (ACC) measurements for alpha ratio, CPP, PPE, SPL SD, fundamental frequency (fo) mean, and SD. Speech type and measurement timing were significantly associated with alpha ratio, while the instrument was not. Microphone measurements resulted in slightly lower CPP compared to the accelerometer, while reading samples yielded higher CPP compared to vowel productions. PPE, SPL SD, and fo mean showed significant associations with speech type, based on univariate analysis. Microphone measurements yielded a statistically smaller fo SD compared to the accelerometer, while reading productions had a larger fo SD than vowel productions. Conclusions: Fundamental frequency, alpha ratio, PPE, and SPL SD values were robust, regardless of the instrument used, suggesting the potential use of accelerometers in less-controlled environments. These findings are crucial for enhancing confidence in voice metrics and exploring efficient clinical assessment protocols. Full article

The Fokas method (also known as the unified transform method) is used to investigate acoustic scattering by thin, infinite grating by extending the methodology to apply to spatially periodic domains. Infinite grating is used to model a perforated screen, a material of interest in aeroacoustics and noise reduction. Once the method is established, its numerical results are verified against the Wiener–Hopf (WH) technique, which has solved the problem only for a special case. A key benefit of the novel approach is that the scatterer, modelled as an infinitely repeating unit cell consisting of a thin, rigid plate, can take any length. This is in contrast to the WH method, where the plate length is restricted to half the width of the unit cell (for this method, no such restriction exists). The numerical method is an over-sampled collocation method of the integral equation resulting from applying the Fokas method: the global relation. The only increase in complexity in adapting the Fokas method to more complicated cell geometries is a higher number of terms in the global relation. The proportion of energy transmitted and reflected by the grating structure is assessed for varying incident wave angles, frequencies, and plate lengths. Full article