Acoustics

This paper explores the application of a specialized end-to-end framework, crafted to study historical soundscapes, with a specific focus on 18th-century Naples. The framework combines historical research, natural language processing, architectural acoustics, and virtual acoustic modelling to achieve historically accurate and physically based soundscape reconstructions. Central to this study is the development of a Historically Informed Soundscape (HIS) map, which concentrates on the urban spaces of Largo di Palazzo and Via Toledo in Naples. Using virtual and audio-augmented reality, the HIS map provides 3D spatialized audio, offering an immersive experience of the acoustic environment of 18th-century Naples. This interdisciplinary approach not only contributes to the field of sound studies but also represents a significant methodological innovation in the analysis and interpretation of historical urban soundscapes. By incorporating historical maps as interactive graphical user interfaces, the project fosters a dynamic, multisensory engagement with the past, offering a valuable tool for scholars, educators, and the public to explore and understand historical sensory environments. Full article

One of the quintessential goals of musical instrument acoustics is to improve the perceived sound produced by, e.g., a violin. To achieve this, the connections between physical (mechanical and geometrical) properties and perceived sound output need to be understood. In this article, a single facet of this complex problem will be discussed using experimental results obtained for six violins of varying back arch height. This is the first investigation of its kind to focus on back arch height. It may serve to inform instrument makers and researchers alike about the variation in sound that can be achieved by varying this parameter. The test instruments were constructed using state-of-the-art methodology to best represent the theoretical case of changing back arch height on a single instrument. Three values of back arch height ($12.1$, $14.8$ and $17.5$ mm) were investigated. The subsequent perceptual tests consisted of a free sorting task in the playing situation and three two-alternative forced choice listening tests. The descriptors “round” and “warm” were found to be linked to back arch height. The trend was non-linear, meaning that both low- and high-arch height instruments were rated as possessing more of these descriptors than their medium-arch height counterparts. Additional results were obtained using stimuli created by hybrid synthesis. However, these could not be linked to those using real playing or recordings. The results of this study serve to inform violin makers about the relative importance of back arch height and its specific influence on sound output. The discussion of the applied methodology and interpretation of results may serve to inform researchers about important new directions in the field of musical instrument acoustics. Full article

A model of the vocal tract that mimicked velopharyngeal insufficiency was created, and acoustic analysis was performed using the boundary element method to clarify the acoustic characteristics of velopharyngeal insufficiency. The participants were six healthy adults. Computed tomography (CT) images were taken from the frontal sinus to the glottis during phonation of the Japanese vowels /i/ and /u/, and models of the vocal tracts were created from the CT data. To recreate velopharyngeal insufficiency, coupling of the nasopharynx was carried out in vocal tract models with no nasopharyngeal coupling, and the coupling site was enlarged in models with nasopharyngeal coupling. The vocal tract models were extended virtually for 12 cm in a cylindrical shape to represent the region from the lower part of the glottis to the tracheal bifurcation. The Kirchhoff–Helmholtz integral equation was used for the wave equation, and the boundary element method was used for discretization. Frequency response curves from 1 to 3000 Hz were calculated by applying the boundary element method. The curves showed the appearance of a pole–zero pair around 500 Hz, increased intensity around 250 Hz, decreased intensity around 500 Hz, decreased intensities of the first and second formants (F1 and F2), and a lower frequency of F2. Of these findings, increased intensity around 250 Hz, decreased intensity around 500 Hz, decreased intensities of F1 and F2, and lower frequency of F2 agree with the previously reported acoustic characteristics of hypernasality. Full article

This study was conducted to improve the sound absorption dips in nonwoven fabric sheets with a back air space. Considering the particle velocity distribution in the back air space, another nonwoven sheet was added to divide the air space into layers. The sound absorption coefficient of the sound-absorbing structure was theoretically derived using the transfer matrix method. The nonwoven sheet model with the Rayleigh model and the air space behind the nonwoven sheet were mathematically represented using the transfer matrix. The transfer function method was employed to combine the transfer matrices to obtain the sound absorption coefficient. A two-microphone acoustic impedance tube was used to measure the sound absorption coefficient, and the theoretical and experimental values were compared. The sound absorption dip of the first order was improved by placing a nonwoven sheet at a position half the thickness of the back air space. It was theoretically predicted that placing the nonwoven sheet at 1/4 of the back air space thickness from the rigid wall would improve the first- and second-order sound absorption dips. By selecting the conditions, a similar trend was observed during the experiments. The study shows that the higher the ventilation resistance of the added nonwoven fabric sheet, the more improved the sound absorption dip. Full article

Hydroponics is a method of growing plants without soil and serves as an efficient agricultural production system. Compared to traditional farming, hydroponic crops offer significant water savings while also reducing the need for chemical pesticides by eliminating soil-borne diseases and pests. Additionally, hydroponic materials are being studied as a potential food source for space missions and as a substitute for industrially produced animal feed during winter. This paper explores the acoustic absorption properties of green materials derived from hydroponic systems. The roots of wheat grown in a porous layer formed a rigid skeleton structure. After drying, test specimens were prepared for acoustic measurements, undertaken using an impedance tube, to assess the material’s sound absorption performance. The results indicate optimal absorption around 600 Hz and 2000 Hz, reaching α = 0.95–1.0, which is significant. A brief description of the substrate layers is also provided. Full article

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