Sound Reflection Research Articles

Selection of measurement positions for measuring sound reflection of noise barriers

The number of positions for the in-situ measurement of sound reflection under direct sound field conditions according to EN 1793-5 for road traffic noise reducing devices (NRDs, e.g. noise barriers) depends on the surface structure of the device under test. The surface structure and material homogeneity may be categorized as flat and non-flat as well as homogenous and inhomogeneous. Flat and homogenous NRDs are measured with one central measurement position, whereas non-flat and or inhomogeneous devices require additional measurements points to assess the overall sound reflection properties. In the current version of the standard, NRDs are considered flat, if the depth of their surface structure is below 8.5 cm. Also, they are considered homogenous if the lateral extent of each material is at least 8.5 cm. It is discussed to reduce this criterion from 8.5 cm to 1.7 cm, as research showed significant differences on devices considered as flat between measurement positions for the sound reflection index. An extensive analysis of sound reflection measurements shows the influence of the measurement position for noise barriers with structural depths below 8.5 cm. A new strategy for selecting measurement positions is proposed, which also considers the period length of the surface structure.

SS 25268:2023, an acoustic standard for listeners and speakers

The sound environment in many classrooms is not good, and we know that poor room acoustics impedes learning and has a negative effect on teachers' voice health. Sound reflections in the room have a great impact on both speech intelligibility and speech comfort. SS 25268 is a Swedish sound standard for, among others, school buildings. The standard uses reverberation time, RT, to put requirement on room acoustics. There is a connection between the amount of sound absorption in the room and RT according to Sabine formula. The problem is that Sabine formula requires a diffuse sound field witch very seldom occurs in classrooms with acoustic ceilings. Another problem is when RT is evaluated with T20, the early reflections are not included, and early reflections have a great impact on speech intelligibility. The standard have been updated to a new version, SS 25268:2023. In this standard there is an opportunity for landlords to put other requirements then RT to evaluate the room acoustics. The standard have an appendix to help landlords, principals and teachers to better understand how to put the right acoustic requirements on their school buildings to create both good speech intelligibility and speech comfort.

A high-resolution acoustic goniometer for characterizing sound diffuser reflections

Noise control engineering and architectural acoustics practice have widely applied diffusing elements and devices to create surface scattering and diffuse reflections. An acoustical goniometer in the form of a circular microphone array has been used to characterize scattered responses for various types of diffusing elements/devices. This research is also intended for experimental validation of diffraction simulations of diffusing devices based on the physical theory of diffraction (PTD). To cope with experimental challenges, particularly for the research in the physical theory of diffraction, an acoustic goniometer must achieve a high enough angular resolution in addition to fulfilling far-field requirements. This paper discusses practical implementations and experimental results of portable goniometers with a radius of up to five meters and an angular resolution of 1.25 degrees. The practical implementation is intended to be easily deployable in empty, indoor spaces of sufficiently large dimensions for scattered reflection characterization. This paper discusses an effort of increasing experimental efficiency of characterization procedures for oblique incidences.

Measurement of sound reflection and sound insulation of installed noise barriers using the SOPRANOISE quick method

This paper presents the preliminary results of a study on the new possibilities emerging from the analysis of measurements on installed noise barriers following the quick method designed in the frame of the SOPRANOISE project. Measurements of sound reflection and sound insulation were done in laboratory on a full-scale acoustic barrier and on an acoustic barrier installed along the Brennero motorway in northern Italy. The measurements were carried out using the SOPRANOISE quick system device, designed and engineered to provide a fast and lightweight version of the Adrienne method (i.e., EN 1793-5 and EN 1793-6), and then checked by applying the standardized Adrienne method, using instrumentation and procedures validated during the round-robin test performed in the frame of the QUIESST project. The preliminary results of the measurements are presented.

Determination of the acoustic characteristics of a gabion noise barrier

In recent road construction projects in NL more and more stone gabions are used as noise reducing measure. First measurements on noise characteristics on gabions using EN 1793-5 showed peculiar results for sound absorption. This was thought to be an effect of the thickness of the gabion and due to scattering of the sound on the non-flat surface. A new investigation was done on stone gabion NRD's and on a regular reflective and absorptive NRD. Focus was on the applicability of EN 1793-5 for determination of the sound reflection characteristics of gabion NRD's. This paper shows the results of measurements on gabion and "regular" NRD's, and of model simulation of these measurements to understand the results, and give guidance on modeling a gabion NRD in a general TNM.

DNN-based HRTF individualization for accurate spectral cues using a compact PRTF

Head-Related Transfer Function (HRTF) plays a critical role in how the auditory system perceives spatial information. The spectral cues embedded in HRTF are vital for accurately determining the elevation of sound sources. In existing approaches, deep neural networks (DNNs) have been utilized to predict the magnitude spectra of HRTF from images of the pinna, typically employing the HRTF log-magnitude as the output during training. However, HRTF encompasses the acoustic characteristics of both the head and torso, exhibiting direction-dependent patterns that pose challenges in reconstructing its spectral cues. To address this complexity, we propose an innovative method for HRTF individualization. Our model uses Pinna-Related Transfer Function (PRTF) as the output during training, which helps alleviate the impact of sound reflections from the head and torso in the head-related impulse response (HRIR). Our experimental findings, based on an HRTF dataset, illustrate that our proposed model excels in reconstructing the first and second spectral cues. Furthermore, it outperforms previous deep learning models in terms of log spectral distortion (LSD).

How sighted people experience the sense of volume? A phenomenal study

This study aims to provide a phenomenological description of the sense of volume in sighted people. Especially developed by non-sighted people, the sense of volume is an ability to perceive solids and voids by analysing sound reflection. Our recent works have brought it closer to the human echolocation's ability, but also to a form of spatial hearing based on the analysis of variations in the ambient sound field. In many studies, blindfolded participants were able to detect a surface positioned in front of them. However, there are no studies reporting on the experience of the sense of volume in sighted people under conditions of ecological perception. Consequently, we carried out commented walks, combined with a micro-phenomenological interview method in an urban environment. By cross-referencing participants' perceptions (wall detection at one metre, typologies' discrimination of) with feelings they share (acoustic feelings combined with synesthetic tactile feelings), we demonstrated the ability of sighted people to rapidly unveil a functional sense of volume. Several researchers have hypothesized that sighted people may use a form of automated passive echolocation. In the light of our results, we wonder whether the sense of volume might be a non-conscious factor in an urban atmosphere.

Time-domain model for spherical wave reflection in a flat surface with absorber character – Application to the SOPRA measurement method

This paper presents a developed time-domain model for the reflection of spherical waves in an absorber-like surface. The model is made to enable evaluation of measurement methods for assessing the sound absorptive properties of traffic noise barriers in direct sound field, it is thus called the Direct Field Absorption (DFA) model. In this study, the DFA model is applied to the in-situ SOPRA method for quick sound reflection index measurements on road noise barriers. The DFA model results in an impulse response (IR), based on a theoretically derived impedance of a certain absorber. The DFA IR is entered to the SOPRA formula to calculate the reflection index, RIQ, of the absorber, which is subsequently compared to the measured RIQ of a wall fitted with the absorber in question. If the results are similar, it is reasonable to assume that the SOPRA measurement results are valid. But if there are any significant differences between the DFA and SOPRA sound reflection indices, possible reasons for them should be examined.The first results are encouraging, showing that the DFA model can be a valuable tool to evaluate the results of reflection measurements. Furthermore, the DFA model could be useful for estimating the sound absorptive performance at lower frequencies of a noise barrier limited to its spatial extent in width and height, i.e., when it is physically impossible to measure. Further studies are necessary though, since the conclusions of this paper are based on only one kind of absorber.

Underwater noise measurements of a free-running ship model

ABSTRACT The high background noise and narrow widths of towing tanks, which cause sound wave reflections, make them unsuitable for noise measurements, leading to a lack of published hydroacoustic data. To address this, we developed a free-running test model of the benchmark DTC container ship at a 1/80 scale and conducted hydroacoustic tests in the artificial lake at Istanbul Technical University. The model was remotely controlled to pass a fixed water station equipped with a hydrophone. We present ship noise measurements at three different velocities, noting a strong correlation between the propeller rotation rates from self-propulsion tests and hydroacoustic signals at high speeds. However, accuracy decreases at lower speeds due to background noise interference.

Plato’s Allegory of the ‘Cave’ and Hyperspaces: Sonic Representation of the ‘Cave’ as a Four-Dimensional Acoustic Space via an Interactive Art Application

Mathematician and philosopher Charles Howard Hinton posited a plausible correlation between higher-dimensional spaces, also referred to as ‘hyperspaces’, and the allegorical concept articulated by the Ancient Greek philosopher Plato in his work, Republic, known as the ‘Cave.’ In Plato’s allegory, individuals find themselves situated in an underground ‘Cave’, constrained by chains on their legs and neck, perceiving shadows and sound reflections from the ‘real’ world cast on the ‘Cave’ wall as their immediate reality. Hinton extended the interpretation of these ‘shadows’ through the induction method, asserting that, akin to a 3D object casting a 2D shadow, the ‘shadow’ of a 4D hyper-object would exhibit one dimension less, manifesting as a 3D object. Building upon this conceptual framework, the authors posit a correlation between the perceived acoustic space of the bounded individuals within the ‘Cave’ and the characteristics of a 4D acoustic space, a proposition substantiated mathematically by scientific inquiry. Furthermore, the authors introduce an interactive art application developed as a methodical approach to exploring the hypothetical 4D acoustic space within Plato’s ‘Cave’, as perceived by the bounded individuals and someone liberated from his constraints navigating through the ‘Cave.’

Generalized interpolation-supplemented cascaded lattice Boltzmann method for noise radiated from a circular cylinder

Flow past a stationary or vibrating body usually leads to intense noise radiation. In order to study this problem via direct simulations, a cascaded lattice Boltzmann method (CLBM) is developed in the moving frame of reference, and implemented in a body-fitted grid using the generalized interpolation-supplemented particle streaming. A far-field perfectly matched layer is also incorporated so as to avoid sound reflection. The proposed generalized interpolation-supplemented cascaded lattice Boltzmann method (GICLBM) is then validated through numerical experiments concerning fixed and forced oscillating circular cylinders, in terms of forces exerting on the cylinder, wall stress, near-field flow dynamics, and far-field sound radiation. Very good consistency is observed for all quantities discussed therein with previous benchmark tests. Furthermore, the noise radiated from a circular cylinder undergoing vortex-induced vibration (VIV) is investigated using the GICLBM, providing interesting results. Firstly, at a mass ratio of m⁎=2, the flow and vibration dynamics are found to be dependent on the Mach number, and the critical value is found to be approximately Ma=0.1. Secondly, through comparisons with scenarios involving a fixed cylinder and a forced vibrating cylinder, it is noted that the VIV generates significantly more complicated sound sources including monopole and drag dipole. Thirdly, in the lock-in condition, the increase in the reduced velocity only alters the magnitude of the radiated sound pressure but not the directivity. Through this study, a high-fidelity, efficient, and relatively simple framework for fluid-structure-sound interactions is proposed.

Sound propagation in the presence of non-isothermal sheared flow refraction and metasurface impedance reflection

Sheared flow can profoundly influence the aeroacoustic performance of near-wall structures like metasurfaces on moving vehicles. In this work, a refractive generalized Snell’s law is developed by combining Snell’s law with the generalized Snell’s law to manipulate anomalous reflections in an idealized sheared flow, comprising a uniform flow region and a stationary air region with velocity and temperature gradients. Theoretical analysis and numerical simulations of planar wave reflection by metasurface impedance under non-isothermal sheared flows are conducted, yielding favorable predictions of the zone of silence, as well as anomalous and total reflection behaviors. The total reflection between the shear layer and the metasurface is analyzed with the objective of confining incident wave below the shear layer. Remarkably, a specific configuration of hot-sheared flow and metasurface length can achieve total absorption over a range of incident wave angles from 0° to almost 90°. Moreover, the refractive generalized Snell’s law, extended to account for directional deflection induced by flow convection, is utilized to regulate sound beam reflection, resulting in satisfactory outcomes under sheared conditions. This study offers a theoretical framework for wave control under non-isothermal and sheared flow conditions, which cannot be resolved by the traditional generalized Snell’s law, and can be implemented in the design of metasurfaces for moving applications.

A rule-based framework for capturing geometric characteristics in design: A study of façade analysis for acoustic behaviour in urban space

In urban acoustics, the design of built environment substantially impacts the environmental noise of our everyday lives, as the built environment constantly reflects the sounds of human or non-human actors in its vicinity. The effects produced by these reflected sounds significantly depend on the geometric characteristics of the surrounding building façades. Despite their impact, the façade characteristics are often excluded from urban acoustic simulation models. As a result, sound reflection and scattering that are specifically related to building façades remain largely unexplored in noise control at the urban scale. Inspired by computational design tools used for exploring room acoustics, we investigate how a computational approach enables the analysis of geometric characteristics of façades to simulate urban acoustics during early design processes. This paper introduces a rule-based characterisation framework that enables the representation of geometric façade characteristics and their relationships with acoustic constraints in the form of rules. Our first results showed how these rules allowed for capturing and reconstructing façade geometries based on the given acoustic constraints. We believe that this novel approach empowers designers to describe their initial design ideas in a formalism that can be dynamically adapted to various dimensions, such as urban acoustics, and to reconstruct the form throughout the design process.

Acoustic dynamics in performance halls: Enhancing violin sound quality in the FPSD orchestra room

With an emphasis on improving violin sound quality, this study explores the acoustic dynamics of the FPSD Orchestra Room at Universitas Pendidikan Indonesia. Direct and reflected sound are the two factors that impact the phenomena of interior sound. This research emphasizes the crucial balance between sound absorption and reflection to optimize the acoustic environment and ensure clarity and richness in violin performances. Improving acoustic conditions is vital to increase audience experience and performance quality. The study used a qualitative descriptive research style combining literature review and observations. The research site was the FPSD Orchestra Room, renowned for its historical significance and contribution to music education. The observations revealed significant acoustic obstacles that adversely affected the violin sound's clarity, including excessive reverberation and unequal sound dispersion. The literature review revealed the theoretical underpinnings of sound propagation, reverberation, absorption, reflection, and diffraction. The acoustic environment can be greatly enhanced by introducing sound-absorbing materials to optimize reverberation duration, controlling reflections with diffusers, and utilizing adaptive acoustic systems. Furthermore, combining virtual acoustics technology with digital sound processing systems allows for dynamic control over acoustic parameters, increasing the performance space's adaptability. These improvements provide a customized acoustic environment that supports a variety of musical performances and guarantees the audience a clear, engaging auditory experience. This study emphasizes the significance of fusing cutting-edge technology innovations with conventional acoustic design concepts to attain optimal sound quality in performance halls. Innovation and research must never stop to improve these acoustic settings even further.

Converging rainbow trapping silencers for broadband sound dissipation in a low-speed ducted flow

Rainbow trapping filters (RTFs) have been so far investigated to achieve broadband unit sound absorption in closed-end duct terminations. However, opened RTFs have been scarcely explored to realize broadband low-frequency dissipation of sound waves while being traversed by a low speed flow. To bridge the gap, we propose a RTF composed of coiled cavities whose inner radius follows a flow-compliant converging profile, referred to as a converging coiled CCRTF silencer. An effective medium approach and the transfer matrix method (TMM) showed the ability of such devices to produce slow sound, impedance matching and minute sound reflection and transmission over a wide bandwidth, confirmed by finite element simulations and scattering matrix measurements without flow. A causal analysis revealed that a large density of wall resonators enhances the silencer performance while its bandwidth is driven by the coiling factor, convergent contraction ratio and cavities axial growth. Particle swarm optimization of these parameters led to a sub-wavelength CCRTF silencer with near-unit dissipation over 3.5 octaves from 200 Hz upwards. Extended TMM and aeroacoustic measurements showed resilience of the CCRTF performance under upstream or downstream propagation conditions for outlet Mach numbers below 0.16, thereby opening up applications like the design of silent convergent nozzles.

IMPROVEMENT OF CAPILLAROSCOPY METHOD FOR STUDYING HUMAN MICROCIRCULATION

The human circulatory system has historically captivated researchers in the field of medicine. Modern medicine, however, has moved beyond identifying a single crucial element, such as the heart or venous system, for maintaining blood flow. Instead, it emphasizes a more analytical approach, focusing on the interconnected functioning of all components within the system. The aim of this work is to analyze the existing methods of studying blood microcirculation and to improve the technology of capillaroscopy, technical means of raster microphotography to determine the physiological state and disorders of capillary circulation. To achieve this objective, we address the following tasks: analyzing existing non-invasive methods for studying the human vascular system; enhancing the optical capillaroscopy method through the utilization of modern high-resolution digital cameras, computer, and multimedia equipment, along with appropriate software for analyzing electronic images; developing a technological scheme and equipment design for digital microphotography of capillaries in the periungual region of the upper extremities; providing software solutions for registering and analyzing digital microphotographic images obtained through capillaroscopy; conducting experimental studies to explore the structure and properties of capillaries utilizing the developed technologies and equipment. Magnetic resonance imaging (MRI) enables the comprehensive evaluation of both anatomical and functional aspects of blood flow. Magnetic resonance angiography (MRA) capitalizes on the distinction between the signal emitted by moving tissue (blood) and that of surrounding stationary tissue, facilitating the acquisition of vascular images without the need for radiopaque contrast agents. Ultrasonography integrates Doppler and conventional ultrasound techniques, providing physicians with insights into blood vessel structure and blood flow dynamics. Traditional ultrasound employs sound waves that are imperceptible to the human ear and bounce off blood vessels, while Doppler ultrasound measures the velocity of sound wave reflection from moving elements. Ophthalmoscopy constitutes a fundamental component of standard ophthalmological examinations, serving as a pivotal tool for diagnosing eye conditions and evaluating the condition of blood vessels. Additionally, ophthalmoscopy aids in diagnosing autoimmune disorders. Capillaroscopy enables comprehensive assessments of both systemic and regional microcirculation disorders, facilitating the characterization of tissue metabolism. Dysfunction in capillary function contributes to circulatory impairments, leading to blood stasis, metabolic irregularities, and compromised immunity, thereby exacerbating existing conditions and predisposing individuals to new diseases. Optical computerized capillaroscopy offers a non-invasive means of visualizing, examining, and archiving capillary images, enabling clinicians to make informed assessments regarding blood microcirculation. Experimental validation of the optimized hardware and software capillaroscopy system was conducted using nail bed capillaries of a patient with type II diabetes mellitus undergoing insulin therapy for 10 years. This study underscores the importance of refining and enhancing optical capillaroscopy methodologies by leveraging high-resolution camera sensors and modern computational tools for image processing.

Ultrasound Elastography: Methods, Clinical Applications, and Limitations: A Review Article

Ultrasound is a highly adaptable medical imaging modality that offers several applications and a wide range of uses, both for diagnostic and therapeutic purposes. The principles of sound wave propagation and reflection enable ultrasound imaging to function as a highly secure modality. This technique facilitates the production of real-time visual representations, thereby assisting in the evaluation of various medical conditions such as cardiac, gynecologic, and abdominal diseases, among others. The ultrasound modality encompasses a diverse range of modes and mechanisms that serve to enhance the methodology of pathology and physiology assessment. Doppler imaging and US elastography, in particular, are two such techniques that contribute to this expansion. Elastography-based imaging methods have attracted significant interest in recent years for the non-invasive evaluation of tissue mechanical characteristics. These techniques utilize the changes in soft tissue elasticity in various diseases to generate both qualitative and quantitative data for diagnostic purposes. Specialized imaging techniques collect data by identifying tissue stiffness under mechanical forces such as compression or shear waves. However, in this review paper, we provide a comprehensive examination of the fundamental concepts, underlying physics, and limitations associated with ultrasound elastography. Additionally, we present a concise overview of its present-day clinical utilization and ongoing advancements across many clinical domains.

Sound absorption performance and mechanism of aluminum foam with double-layer structures of conventional and porous cell walls

Open-cell aluminum foam exhibits sound absorption valleys in the 2500-4000 Hz range, reducing its sound absorption performance in the 800–6300 Hz range. This paper prepared a novel aluminum foam with a double-layer structure using the infiltration casting method, and its pore structure, sound absorption performance, acoustic model, and sound absorption mechanism are investigated. The double-layer structure consists of a conventional pore (CP) layer with a single pore size of 250 μm or 600 μm and a porous cell wall (PCW) layer with double pore diameters of 250 μm and 600 μm. As the thickness ratio between the CP and PCW layers decreases, the acoustic absorption valley value of the double-layer structure increases when combined with a small-pore CP layer. In contrast, it decreases slightly when combined with a large-pores CP layer. The double-layer structure reaches a sound absorption valley value and average sound absorption coefficient of 0.912 and 0.902, respectively. The double-layer structure's sound absorption valley value is better than that of a homogeneous structure, improving sound absorption performance. A Lu modified model is established to characterize the sound absorption of the double-layer structure, which closely matches the experimental results. The modified model further analyzed the vital geometrical parameters affecting the absorption valleys. Acoustic impedance analysis shows the enhanced sound absorption valleys are due to: 1) Gradient acoustic impedance reduces sound reflections at the air-structure interfaces and increases secondary reflection at the interfaces in the structure; 2) The series–parallel configuration increased the resonance peak bandwidth, while the dual-sized resonance cavities regulated the resonance peak frequency.

Study on sound absorption valley and acoustic absorption performance of small-pore aluminum foam composited with 304 stainless steel fibers

Open-cell aluminum foam exhibits a sound absorption valley (SAV) in the 2500–4000 Hz frequency range, reducing its acoustic absorption in the range of 1000–6300 Hz. A small-pore aluminum foam composited with 304 stainless steel fibers (SP-SS304F aluminum foam) with a porosity of 82 % was fabricated via infiltration casting, and its pore structure, acoustic absorption performance, and mechanism were investigated. The pore structure of SP-SS304F aluminum foam consisted of 223–676 μm main pores, 125–373 μm cell wall pores, and 30–60 μm 304 stainless steel fibers. The fibers existed completely embedded in the cell walls, partially or completely embedded in the cell cavities. As the pore diameter decreases, the SAV value increases and then decreases. With increasing fiber content, the SAV value showed a similar trend. The increased SAV value benefits the enhancement of the average sound absorption coefficient (SAC). The SP-SS304F foam aluminum reaches an optimal SAC value of 0.899. Its static resistivity value is 24,345 Pa.s/m2. Finite element simulations reveal the reasons for the improved acoustic absorption performance of SP-SS304F aluminum foam: First, the small-diameter and pore-embedded fibers improve the acoustic impedance matching, reducing sound reflections at the SAV frequency. Second, the reduced pore diameters and partially or completely pore-embedded fibers increase the pore surface areas, intensifying the acoustic absorption by pore structure.

Auditory Spatial Illusion – A Psychoacoustic Study in Young Adults

The Franssen illusion, or Franssen effect (FE), is one of the auditory spatial illusions. Few studies have explored the FE, and the mechanisms underlying it remain unknown. The present study was conducted to clarify the FE occurrence with different tasks and presentation modes in young adults. It also sought to investigate possible neurophysiological similarities between interaural time difference (ITD) cue processing and FE perception. FE perception was evaluated using two different tasks and two presentation modes (i.e., insert phones and loudspeakers). Sound reflections (reverberation) were presented in the diffuse field (loudspeaker mode). ITD performance was investigated using different stimuli delivered via insert phones. No significant difference between the two FE perception tasks was found ( F 1,25 = 0.138, p = 0.713). However, the FE perception showed a significant difference between the two presentation modes (F 1,25 = 434.03, p < 0.001). Spearman’s correlation did not reveal a significant relationship between FE perception and ITD scores ( p > 0.05). The current findings show the importance of reverberation in the FE occurrence. Also, the non-significant correlation between the results of the behavioral binaural temporal resolution test and FE perception in young people with normal temporal resolution may indicate that room reflections (reverberation) complicate the ability to process ITDs (rather than poor ITD processing for the “steady state” portion of signal).