Advances in Mathematical Physics

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Narrowband active noise control (NANC) systems are extensively used to cancel narrowband noise. Direct, parallel, and direct–parallel NANC systems use nonacoustic sensors to measure rotational speeds, and a bank of signal generators then produces synchronized sinusoidal waveforms as reference signals corresponding to the fundamental frequency of the undesired noise. The performance of direct NANC systems is based on the frequency difference between two adjacent reference input sinusoids. Parallel NANC systems apply several sinewave generators and two-weight adaptive filters in parallel to attenuate these narrowband components. Conventional direct–parallel NANC systems split these sinusoids into several mutually exclusive sets such that the distance between frequencies within sets is maximized. This paper proposes an improved direct–parallel NANC system in which reference sinusoidal signals are separated by amplitude to enhance efficiency and improve noise reduction performance. Several experiments were conducted using a muffler model to verify the performance of the proposed NANC system.

The acoustic product development process, crucial for effective noise control, emphasises efficient testing and validation of materials for sound absorption in the R&D phase. Balancing cost-effectiveness, speed, and sustainability, the focus is on minimising excess materials. While strides have been made in reducing sample sizes for estimating random-incident absorption, challenges persist, particularly in establishing validity thresholds for smaller samples with increasing thickness, susceptible to potential overestimation due to edge effects. This study delves into analysing the absorption coefficients of widely used acoustic absorber types—polyester, fibreglass, and open-cell foam—in a full-scale reverberation chamber at Ventac, Blessington, and Wicklow. Demonstrating significant absorption above 500 Hz, these porous absorbers exhibit diminished effectiveness at lower frequencies. The strategic combination of these absorbers with different facings enhances their theoretical broadband absorption characteristics in practical applications. Moreover, the study assesses the validity threshold for reduced sample sizes, employing statistical analysis against ISO 354:2003 standard control samples of the absorber types. Analysis of Variance (ANOVA) on material groups underscores the significant influence of frequency components and sample sizes on the absorption coefficient. The determined validity threshold for 12.8 sqm ISO 354 standard control size is 7.7 sqm for the 25 mm open-cell foam. Similarly, the validity threshold of the 12 sqm ISO 354 standard control size is 9.6 sqm for the 20 mm 800 gsm polyester, 7.2 sqm for the 25 mm fibreglass, and the vinyl black on 25 mm fibreglass.

This study aimed to assess and improve the accuracy of a water leakage detection model proposed in preliminary research. The poor results for water leakage sound (recall) and background noise (specificity) were clarified using countermeasures in accordance with each condition. Additionally, frequency amplification in the range of 500–600 Hz, the attenuation of weak components, and a band-stop filter were used to remove the 50 Hz component and harmonics. Pre-processing was carried out in the form of amplification, with weak noise removed using a band-stop filter. The results showed that the application of the proposed model improved the detection accuracy by 80% at the observation points that initially had poor accuracy. Thus, the proposed method was effective at improving the performance of the Recurrence Plot-Convolutional Neural Network (RP-CNN) model for detecting water leakages.