Acoustic Quantities Research Articles

Reconstruction of reverberant sound fields over large spatial domains.

Characterising acoustic fields in rooms is challenging due to the complexity of data acquisition. Sound field reconstruction methods aim at predicting the acoustic quantities at positions where no data are available, incorporating generalisable physical priors of the sound in a room. This study introduces a model that exploits the general time structure of the room impulse response, where a wave-based expansion addresses the direct sound and early reflections, localising their apparent origin, and kernel methods are applied to the late part. This late energy is considered to follow a sinc-like spatial correlation, in accordance with the random wave field theory. Synthesised pressure points, which follow the observed statistics of the sound field, are introduced to enable extrapolation over large distances. The model is evaluated experimentally in a lecture room and an auditorium, demonstrating a successful reconstruction of the sound field across a 5 m aperture using three microphone arrays of only 4.2 cm radius each. These results indicate that the proposed methodology enables volumetric extrapolation over several orders of magnitude, which is significant in the context of navigable sound field reproduction, "6-degrees of freedom" spatial audio and sound field analysis in rooms.

A Single Acoustic Quantity Index as Part of an Early-Stage Digitalized Procedure for the Restoration of Baroque Theatres to Be Used as Multipurpose Spaces

Historic theatres with a horseshoe shape, the so-called baroque theatres, constitute an architectural heritage and are of enormous importance. For these reasons, this paper aimed to identify a single acoustic quantity index as part of an early-stage digitalized procedure to improve the management of the complexity of their restoration process, both better preserving the original room acoustic field and making it variable for new different uses of the theatre space. The procedure introduces technical policies and design tools in a BIM execution plan (BEP) and is supported by a digitalization that inserts the restoration of theatres into industry 4.0. This choice was taken according to the new design goals and the new Procurement Code Directives, which underlie the use of digital technologies in this context. The described acoustic single number quantity, called a “multipurpose index”, summarizes the main room acoustic goals for when a baroque theatre is used as a multipurpose space after renovation, specifying and better controlling the requested room acoustic quality for people other than acoustics specialists, such as theater directors, and more generally for the management. As an example of this possible transition, the case study of “Teatro Ristori” is presented.

The Effect of Entropy Waves Features on the Indirect Noise Generation within an Aeronautical High-Pressure Turbine stage

Abstract First stages of aeronautical high-pressure turbine are subjected to inlet distortions generated by the combustor systems. Such disturbances, characterized by velocity and temperature fluctuations, are referred to as vorticity and entropy waves and they are convected downstream by the main flow. Such disturbances interact with the turbine stages affecting the stage efficiency, heat exchange and generating noise emissions. This work summarizes a comprehensive numerical campaign on the effect of different Entropy Waves features (i.e. radial position, clocking and swirl direction) on the indirect noise generation of engine-representative high pressure turbine stage tested at the Politecnico di Milano LFM (Laboratory of Fluid Dynamics of Turbomachinery). The numerical campaign is based on URANS CFD simulations with time-varying inlet distortions, carried out with the University of Florence in-house TRAF code. A Discrete Fourier Transform (DFT) based post-processing tool has been used to extract the low frequency entropy wave content to assess indirect noise emissions. The extensive validation of the TRAF code in previous campaigns grants the fidelity of the results in terms of aerodynamic and acoustic quantities. The numerical results provide a deeper insight of the effect of entropy waves features on indirect noise generation. The outcome of the results may be used by the designer to better understand the combustor-turbine interaction, also considering the possible introduction of innovative fuels such as hydrogen or Sustainable Aviation Fuel (SAF).

Prediction of the acoustic particle velocity in aerodynamic flows and its applications to the boundary element method

The acoustic variables are essential for understanding sound energy transmission and redistribution. The previous methods focused on acoustic pressure without the acoustic particle velocity, which is not enough for acoustic field evaluation. In this paper, an analytical formula for acoustic particle velocity prediction is developed based on the permeable surface integral solution of a vector wave equation. The validation examples are presented with stationary dipole and rotational monopole. The acoustic quantities, pressure, and velocity are solved at the same time and will be applied as input for the boundary element method (BEM) to evaluate the sound scattering problem in the frequency domain. Furthermore, the method is applied to study the acoustic field of flow passing a cylinder. The acoustic pressure shows good agreement with the flow observer. The acoustic particle velocity is also investigated.

Basic research on the effect of distance between performers on ensemble performance

Due to the spread of COVID-19, the performers on stage were required to keep a certain distance among them. Because it was considered that the droplets come from performers rise a risk of infection with COVID-19 when they performed musical instruments. A distance of at least 2 m between wind instrument performers, and 1.5 m between string instrument performers was recommended. However, with these distances, the performers found it difficult to perform. Actually, in previous studies, it has been suggested that difficulties in listening to their performance can occur. However, the specific causes of these problems have not yet been clarified. Therefore, the purpose of this study is to clarify the effects of differences in distance between performers on acoustical properties and auditory perception by focusing on performers in an ensemble. In particular, targeting a group of five performers arranged in a semi-elliptical shape, the various acoustic physical quantities, and conducting subjective evaluation experiments were performed. As a result, it was found that changes in the distance between performers affect the acoustic properties and the auditory perception. This knowledge will contribute to creating a comfortable environment for performers.

Swiss railway field laboratory: analysis of two years' data collection

Since May 2022, a 1 km long section of the regular train network of Switzerland between Lucerne and Olten has been equipped with a variety of sensors and microphones. The superstructure of this test track was renewed in December 2019 and consists of ballasted track with concrete sleepers, in part with and without stiff under sleeper pads, respectively. Since June 2022 the sensors and microphones have continuously recorded pass-by data for sound, vibration and track dynamics for every passing train. This long-term measurement installation allows studying different environmental influences on noise and vibration. The very large amount of data enables both statistical analysis and building statistical models. Furthermore, the railway field lab can be used determine the influence of different track components. In this paper, we report on our statistical analysis of the data gathered since June 2022 including statistical models of the influence of the environment and of different rolling stock on sound and vibration. Furthermore, we present the results of a novel high damping rail pad tested at the railway field lab. Based on these results, we present a proposal and discuss our thoughts on the best practice for measuring acoustic quantities.

Метод обработки сигналов токов статора асинхронного двигателя для диагностики обрыва стержня ротора

The study is relevant due to high requirements to the reliability of the operation of auxiliary mechanisms of thermal power plants (TPP). The main source of mechanical power of auxiliary mechanisms of TPPs is high-voltage induction motor with squirrel cage rotor (IMSC). One of the most difficult causes of emergency shutdown to detect early is a broken rotor bar. The breakage of IMSC rotor bar is of latent character. It can be for a long time without considerable influence on the machine operation mode. Nevertheless, the fact of the breakage can be considered as an emergency condition of IMSC, and the consequences of leaving the groove of the magnetic core are irreversible. Scientifically, early diagnostics of IMSC rotor bars breakage of TPP auxiliary needs is both a difficult and extremely urgent task. The existing methods of diagnostics of such damage are based on measurement and analysis of vibration and acoustic physical quantities. The most common electrical parameter, used as a source of information, as a rule, is current consumption. And most of methods are based on Fourier analysis. The purpose of the study is to develop a mathematical algorithm to process digitized curves of stator phase currents to diagnose high-voltage IMSC. The theory of electric machines, the method of analytical approximation of experimental data, the method of regression analysis have been used to solve the problem. Experimental data is obtained, and testing of the algorithm is conducted on an experimental installation with a 0,4 kV induction motor with a modified design of the active part of the rotor developed for physical simulation of IMSC broken rotor bar. This paper proposes a new method of digital processing of stator current signals based on the regression analysis method for diagnostics of IMSC rotor winding. The authors have developed an algorithm for mathematical processing of digitized stator current curves based on regression analysis in the cosine-sine basis to identify the diagnostic sign of failure of one rotor bar of IMSC rotor. The authors have determined the number of harmonic components that best describe the initial signal from the point of view of the balance between saving computational resources and accuracy of approximation. A mathematical algorithm to detect the rotor bar breakage of an induction motor based on regression analysis of stator currents has been obtained and tested. It allows to detect rotor circuit damage with 97 % accuracy. At the same time the diagnostic sign changes its level when one bar breaks by 5 %. It is recommended to adapt the algorithm to the programming languages of microprocessor relay protection units.

SOUND ABSORPTION COEFFICIENT MEASUREMENT METHODS IN REVERBERATION ROOM AND IMPEDANCE TUBE

Sound absorption materials are very often used for space design in order to reduce the noise level and adjust the acoustic characteristics of the space depending on its purpose. Therefore, knowledge of the acoustic quantities that characterize sound absorption materials is of crucial importance. The most commonly used acoustic quantity is the sound absorption coefficient, which can be determined using standardized methods and methods used only for research purposes. This paper will provide an overview of the most commonly used standardized methods for determining the sound absorption coefficient: the reverberation room method and the impedance tube method. Since the impedance tube method, which provides the normal incidence sound absorption coefficient, is more suitable when developing new absorption materials, and in practical applications, it is desirable to know the random incidence sound absorption coefficient, this paper discusses approaches for predicting the random incidence sound absorption coefficient based on the acoustic parameters of the sound absorption materials measured in an impedance tube.

Towards the prediction of flame transfer functions: Evaluation of a hybrid LES-CAA with compressible LES

The prediction of flame transfer functions, particularly in practically relevant systems, remains challenging and computationally demanding. Numerical approaches are a valuable addition to experimental acoustic characterizations of industrial configurations. Conventionally, fully compressible numerical simulations are used that naturally include acoustic fluctuations in their computations, but can be computationally expensive depending on the configuration. Therefore, a convenient approach to use tailored numerics for the underlying physics is considered in this work. In this work, this is realized by applying a runtime-coupled method of computational fluid dynamics and computational aeroacoustics to a single-sector aero-engine combustor. This hybrid computational fluid dynamics and computational aeroacoustics method captures fluid flow behavior and combustion dynamics in a low-Mach computational fluid dynamics domain while allowing for acoustic perturbations in the computational aeroacoustics. Runtime exchange of hydrodynamic and acoustic quantities between the two solvers allows for a bidirectional coupling and, by extension, a complete description of the combustion system. In this work, the hybrid computational fluid dynamics and computational aeroacoustics is applied in a high-fidelity large eddy simulation configuration. The flame transfer function is evaluated for both compressible and hybrid simulations. The results for both numerical approaches are validated with each other and compared to the experimentally obtained flame transfer function. Finally, the computational effort for the numerical approaches is considered. This article presents the first application of a high-fidelity computational fluid dynamics framework using large eddy simulation with bidirectional coupling with the acoustic solver to an industry-relevant configuration. The aim is to provide a roadmap towards investigating thermoacoustic instabilities in a real gas turbine engine at reduced computational costs.

DETERMINING THE DENSITY AND MOLAR MASS OF AIR IN A HOME EXPERIMENT

Formulation of the problem. Experimental research is an integral part of physics education. During distance learning, students can carry out hands-on experiments only at home. Modern smartphones, equipped with various sensors, offer significant capabilities for this purpose. The literature offers quite extensive descriptions of experiments aimed at determining mechanical, acoustic, and optical quantities using smartphones. At the same time, insufficient attention has been paid to determining gas parameters that can be measured using the pressure sensor embedded in smartphones. Therefore, the relevant task is to develop a methodology for experimenting to determine the density of air and its molar mass at home using a pressure sensor. Materials and methods. To achieve the objective of the study, we used the analysis of the curriculum of the course "General Physics for Bachelor of Engineering", a review of the methodological instructions for performing laboratory work in the section "Molecular Physics and Thermodynamics" of the physics course of technical universities, a review of the literature on the topic of the study, and an analysis of the results of student research on the dependence of air pressure on altitude. We also surveyed students about the possibility of conducting the research at home and their interest in conducting other experiments using a smartphone. Results. The methodology for determining the density and molar mass of air was developed based on the results of a study of the pressure-height dependence. It is shown that it is necessary to perform statistical processing of experimental data to estimate the sought quantities. The experimental results allowed us to obtain values of density and molar mass of air that show a good correlation with the tabulated values. Conclusions. Studying the pressure-altitude relationship using a smartphone and the PhyPhox application allows for fairly accurate calculations of air density and molar mass. According to the survey results, students responded positively to conducting home experiments using smartphones.

Musical protein: Mapping the time sequence of music onto the spatial architecture of proteins

Background and objectiveMusic, the ubiquitous language across human cultures, is traditionally considered as a form of art but has been linked to biomolecules in recent years. However, previous efforts have only been addressed on sonification of nucleic acids and proteins to produce so-called life music, the soundscape from the basic building blocks of life. In this study, we attempted to, for the first time, conduct a reverse operation of this process, i.e. conversion of music to protein (CoMtP). MethodsA novel notion termed musical protein (MP) –– the protein defined by music –– was proposed and, on this basis, we described a computational strategy to map the time sequence of music onto the spatial architecture of proteins, which considered that each note in the stave of a music (target) can be simply characterized by two acoustical quantities and that each residue in the primary sequence of a protein (hit) was represented by amino acid descriptors. ResultsA simulated annealing (SA) algorithm was applied to iteratively generate the best matched MP hit for a music target and structural bioinformatics was then used to model spatial advanced structure for the resulting MP. We also demonstrated that some small MPs derived from music segments may have potential biological functions, which, for example, can serve as antimicrobial peptides (AMPs) to inhibit clinical bacterial strains with moderate or high antibacterial potency. ConclusionsThis work may benefit many aspects; for example, it would open a door for the hearing-impaired persons to ‘listen’ music in a biological vision and could be a mean of exposing students to the concepts of biomolecules at an earlier age through the use of auditory characteristics. The CoMtP would also facilitate the rational design of proteins with biological and medicinal significance.

Real-time nearfield acoustic holography using particle velocity.

In this paper, a series of impulse response functions between acoustic quantities on the source plane and particle velocity on the hologram plane are derived. In virtue of these functions, real-time nearfield acoustic holography (RT-NAH) is extended from pressure-based to particle velocity. Pressure, normal velocity, acceleration, and displacement radiated from planar sources can be reconstructed by measuring time-dependent particle velocity signals on the hologram plane. A simulation of an excited aluminum plate is performed to evaluate the difference in accuracy between RT-NAHs based on pressure and based on particle velocity. This study also examines the impact of impulse response functions on the reconstruction results, allowing for detailed analysis of the reconstruction accuracy based on these functions. The simulation results demonstrate that using RT-NAH based on particle velocity obtains significantly higher-accuracy reconstruction results when reconstructing normal velocity and displacement and slightly more accurate reconstructed pressure and normal acceleration.

Concert Halls as Nearly Adaptive Spaces

Concert halls have led to increasingly complex spaces that cannot be thought of as static ‘containers’ anymore. This complexity makes them viable to be launched towards industry 4.0 and to be considered a function of the activities that they can provide during their life cycle. They are characterized by dynamic objects that contain sophisticated sub-systems and add to the capability to influence both environmental variables and user behavior. This article explains an adaptive concert hall at an early stage, in which a network of sensors that gather real-time data on environmental factors such as temperature, air humidity and air velocity are considered, focusing on their direct and indirect intercorrelations with the acoustic quantities to optimize the room acoustic response. The proposed methodology is controlled by a digital twin (DT) based on building information modeling (BIM), integrated with sensors, actuators, and acoustic measurements and algorithms. By analyzing the data, algorithms identify patterns, and an autonomous fine-tune setting is achieved, including the novelty for which a natural variable acoustic field becomes possible during a musical execution without the use of any electroacoustic system support. The hall becomes a natural active instrument to be included in the composer’s score. A case study is presented.

The influence of tympanic-membrane orientation on acoustic ear-canal quantities: A finite-element analysis.

Assuming plane waves, ear-canal acoustic quantities, collectively known as wideband acoustic immittance (WAI), are frequently used in research and in the clinic to assess the conductive status of the middle ear. Secondary applications include compensating for the ear-canal acoustics when delivering stimuli to the ear and measuring otoacoustic emissions. However, the ear canal is inherently non-uniform and terminated at an oblique angle by the conical-shaped tympanic membrane (TM), thus potentially confounding the ability of WAI quantities in characterizing the middle-ear status. This paper studies the isolated possible confounding effects of TM orientation and shape on characterizing the middle ear using WAI in human ears. That is, the non-uniform geometry of the ear canal is not considered except for that resulting from the TM orientation and shape. This is achieved using finite-element models of uniform ear canals terminated by both lumped-element and finite-element middle-ear models. In addition, the effects on stimulation and reverse-transmission quantities are investigated, including the physical significance of quantities seeking to approximate the sound pressure at the TM. The results show a relatively small effect of the TM orientation on WAI quantities, except for a distinct delay above 10 kHz, further affecting some stimulation and reverse-transmission quantities.

The effect of the balloon on balloon-borne infrasound measurements

Deploying acoustic sensors on free-flying, long-living balloons helps to reach the areas not accessible with the traditional ground-based sensors, reduce flow noise, and improve characterization of various infrasound sources. In particular, instrumented balloons can potentially increase the infrasonic detection range and the early warning lead time for natural hazards, such as tornadoes and avalanches. When assessing the capabilities of balloon-borne infrasonic sensors and interpreting the measurements, it is important to recognize that the balloon inevitably distorts both signals and the ambient infrasound field by scattering the incoming sound. Measurement distortions due to a nearby compact scatterer prove to be rather different from the well-understood effect of a rigid boundary on ground-based sensors. Using the recently developed theory of sound scattering by thin, prestressed elastic shells [O. A. Godin, J. Acoust. Soc. Am. 154, 3223–3236 (2023)], this paper quantifies the effects of hot-air and helium balloons on acoustic pressure and oscillatory velocity. It is found that balloon-borne vector sensors are more susceptible to the distortions than pressure sensors, leading to large differences between the apparent and true source bearing and directionality. Possible approaches to compensate for the distortions and retrieve the free-field acoustic quantities will be discussed.

Acousto-optic sensing: A scattering interpretation

Acousto-optic sensing consists in using (laser) light as the sensing element in order to measure, visualise and study acoustic phenomena in a remote, non-invasive manner. One of the most common sensing techniques involves measuring acoustically-induced phase shifts of an optical probing beam by means of interferometry. Arguably, the main fundamental limitation of such sensing technique is that it provides projections of the acoustic field, instead of acoustic quantities at specific locations. In this study we examine the theory of spontaneous light scattering in transparent media, and use this framework to formulate a general acousto-optic sensing problem. Preliminary results based on numerical simulations indicate that light scattering could be applied to the measurement of acoustic pressure fluctuations. Some of the main challenges associated with the principle—mainly related to the weaknesses of the acousto-optic effect in air and relatively low signal-to-noise ratio—as well as the main fundamental differences from conventional interferometry techniques are discussed in this study.

Effect of Hydrogen Enrichment on Transfer Matrices of Fully and Technically Premixed Swirled Flames

Abstract Knowledge of flame responses to acoustic perturbations is of utmost importance to predict thermoacoustic instabilities in gas turbine combustors. However, measuring transfer functions linking acoustic quantities upstream and downstream of flames are very challenging in practical systems and these measurements can significantly deviate from state-of-the-art models. Moreover, there is a lack of studies investigating the effect of hydrogen enrichment on the response of natural gas (NG) flames. In this work, measurements of flame transfer matrices (FTMs) of turbulent H2/NG flames in an atmospheric combustor featuring an axial swirler burner have been performed, allowing us to unravel the transition between FTM in fully premixed (FP) and in technically premixed (TP) conditions. Furthermore, imaging of OH* chemiluminescence and OH-planar laser induced fluorescence are obtained for characterizing the topology of the flame for varying H2 fraction and mixing conditions. Transfer matrices are measured using the multimicrophone method for H2 fractions ranging from 12% to 43% in power. Afterward, the flame transfer functions (FTFs), which linearly relate the coherent fluctuations of the heat release rate to the acoustic velocity oscillations, are obtained from the FTM by using the Rankine–Hugoniot jump conditions across the flame. Using the OH* chemiluminescence intensity as a surrogate for the heat release rate, the FTF based on this optical measurement is also extracted and compared to the one exclusively obtained with the multimicrophone method. As expected, the two different methods are in very good agreement for the FP case and significantly differ for the TP case. Indeed, chemiluminescence fluctuations cannot be directly linked to heat release rate fluctuations when the acoustic forcing induces equivalence ratio fluctuations at the flame, making the optical method unusable for TP configurations. We also show that the two methods agree in the high end of the explored excitation frequency range and we provide an explanation to this intriguing finding. Moreover, we investigate the sensitivity of the FTM measurement to the estimate of the speed of sound in the rig in FP conditions. Finally, the measured FTFs are fitted with FTF models based on multiple distributed time delays. This allows us to explain the frequency dependence and the hydrogen fraction dependence of the gain and the phase in FP and TP conditions.

Toward assimilation of acoustic travel times into an ocean state estimate

Direct ocean observing systems are a scarce set of data that build the backbone for understanding the current state of the ocean. These systems are limited in areas of high variability in temperature and salinity. Pioneering work of Wunsch (1977) proposed efforts to extract detailed hydrographic information using sound propagation through the ocean, providing the scaffolding to improve our understanding of the ocean's interior. The integrated nature of such measurements makes acoustic thermometry a powerful application for monitoring regional to basin-averaged hydrographic changes in the ocean, a measurement that is difficult to achieve by individual “point” measurements (moorings, ship-borne CTD casts, or autonomous floats) alone. This work models acoustic travel times corresponding to eigenrays between a fixed source and receiver from an evolving ocean state. Inclusive computation of acoustic travel times within a dynamically evolving modeled ocean state provide a novel approach to model data comparison within a general ocean circulation model. An adjoint assimilation framework combines observations with numerical models to estimate and update oceanic state variables Forget et al. (2015). This process provides the necessary operators for model data comparison of ocean acoustic observable quantities within a consistent state estimation framework allowing for data assimilation from acoustic tomography measurements.

Real-time online monitoring technology for sweeping frequency ultrasound (SFU) assisted extraction of amur grape (Vitis amurensis) seed oil

Sweeping frequency ultrasound (SFU) was used to assist extraction of amur grape (Vitis amurensis) seed (AGS) oil. Extraction conditions and physicochemical properties were optimized and analyzed under different extraction methods. Meanwhile, frequency and time domains were online monitored during SFU assisted extraction of AGS oil. PVDF piezoelectric sensor was used in time domain, and the hydrophone in frequency domain, so as to obtain the time–voltage waveform, signal power, spectrum distribution and other visual models. Physical models of the spatial peak acoustic intensity, charge quantity and work done by electric field force under different ultrasonic conditions were derived. The mathematical model between the work done by electric field force and the spatial peak acoustic intensity under the working state of PVDF piezoelectric sensor was constructed. Results show that the content of AGS oil by SFU assisted extraction was higher than that by organic extraction. Furthermore, the optimal single-frequency was 40 kHz and dual-frequency was 28/33 kHz, and SFU extraction time of 30 min was suitable with higher oil yield of 16.70 % and 16.94 %, respectively. In addition, the selection and combination of SFU also affected the oil oxidation degree. The peak voltage, spatial peak acoustic intensity, signal power and work of electric field force at 28/33 kHz were all higher than those at 40 kHz.

Assessing the subjective response of consumer product acoustic stimuli in the presence of background variables

Sound quality studies linking subjective response of consumers to objective psychoacoustic metrics are commonplace in product engineering. A typical consumer product sound quality study attempts to formulate an equation to predict consumer response without the presence of background variables. Common treatment of background variables includes controlled listening environments and blind studies. While these studies provide insights into psychoacoustic perception of consumer products, they lack the ability to predict a product’s reception during real-world service. The intent of this study is to quantify the effects of introducing background variables as experimental factors, while developing guidelines of acoustic quantity target setting of home appliances. The background variables in this study were treated according to a factorial design of experiments across eight groups of test subjects. The results showed that indicating the appliance brand to the test participant can have a statistically significant impact on the perception of sound quality of an appliance during normal operation. In addition, a linear relationship of sound level versus subjective response was developed to provide further insights to perceivable changes in sound level in the presence of typical background variables experienced in the home and marketplace. To further link the subjective response to the Voice of the Consumer (VOC), a focus group study with applied laddering theory was conducted to relate test subjects’ sentiment to their underlying values.