Acoustic Reconstruction Research Articles

A factor analysis based automatic optimization method of vibration sensor points for ship acoustic reconstruction

To address the challenge associated with optimizing the number and positioning of accelerometer points in ship acoustic reconstruction, factor analysis is applied to the automatic optimization of accelerometer position in this work according to the source independence of ship’s underwater radiated noise. Based on the numerical simulation method that calculates the vibration noise response under specific operation conditions, the minimum number and the optimal position of the accelerometers can be obtained through the factor analysis and multi-parameter comprehensive evaluation method. The results of acoustic reconfiguration and testing are compared using one test cabin as a validation object to verify the effectiveness of the proposed method. The results show that the automatic optimization algorithm can improve the reconstruction accuracy concerning the uniform distribution method. The error is reduced from 15.46% (1.5 dB) to 8.35% (0.8 dB), and the correlation coefficient is improved from 0.86 to 0.89. The semi-automatic optimization method is slightly lower in terms of errors and correlation coefficients compared to the automatic optimization algorithm. After increasing the number of monitoring positions for automatic optimization, the acoustic reconstruction accuracy is further improved, while the average error is reduced to 7.37% (0.7 dB) and the correlation coefficient is improved from 0.89 to 0.92. The experimental results are proximate to the conclusions of the simulation calculation. Even under the circumstance of multi-factor noise interference, the correlation coefficient of multi-position automatic optimization can still reach 0.8, in comparison with the uniform distribution method, the error is reduced from 32.49% (3.4 dB) to 25.94% (2.6 dB). The proposed method effectively captures the dynamic characteristics of complex structures and their impact on underwater radiated noise, and the integration of factor analysis can prominently enhance the computational efficiency, thereby providing technical support for engineering applications to the ship acoustic reconstruction.

Analysis of direct and indirect noise in a next-generation aviation gas turbine combustor

A large-eddy simulation (LES) of a next-generation combustor is performed to examine effects of this combustor concepts on direct and indirect combustion noise characteristics. Direct noise is computed considering the unsteady heat release predictions while entropy fluctuations in the downstream part of the combustor are used to estimate indirect noise through the transfer function of the outlet nozzle. A low-order acoustic reconstruction technique, which utilizes the Green’s function of the configuration, is developed to compute the acoustics inside the combustor. Comparisons to experimental results are reported, showing the reasonable accuracy of the LES and combustion noise computations. The direct noise spectrum peaks at frequencies around 3 kHz because of the fast timescales associated with the chemical reactions inside the combustor. In addition, the indirect noise is dominant at low frequencies, i.e., less than 400 Hz, because of the characteristics of the entropy spectrum at the outlet nozzle. Compared to a conventional rich-quench-lean (RQL) combustor configuration, significant differences in the acoustics are observed, and are explained by two specific technological novelties. Firstly, the direct noise spectrum peaks at significantly higher frequencies due to the combustor’s compactness. Secondly, the entropy inhomogeneities downstream of the combustion region are an order of magnitude smaller in amplitude due to the lack of dilution with cold air. This leads to a significant reduction in the indirect noise amplitude at low frequencies, where it is the dominant source of noise. These results suggest opportunities for advanced combustion technologies to achieve substantial reductions in combustion-related noise.

Acoustical Power of Lightning Flashes

AbstractLightning is a ubiquitous source of infrasound. To study lightning flashes, thunder measurement efficiently complements electromagnetic observation. Using acoustical arrays, time delays between sensors inform on the direction of sound arrival, while the difference between emission time and sound arrival provides the source distance. Combining the two allows a geometrical reconstruction of individual lightning flashes, each viewed as a set of sound point sources. The measured sound amplitude can also be back‐propagated, compensating for absorption and density stratification. This allows to evaluate the acoustical power of each detected source, and the total power of an individual flash. This methodology is carried out to analyze data from two campaigns in Southern continental France (HyMeX‐SOP1, 2012) and in Corsica (EXAEDRE, 2018). Acoustic reconstruction is compared with ground and altitude localizations provided respectively by electromagnetic low frequency range Lightning Location Systems (LLS), and very high frequency range Lightning Mapping Array (LMA). In Corsica, power from reconstructed sources is also forward‐propagated toward several isolated microphones, and compared to measured signal, giving an additional validation of the power evaluation. Seventy eight events from the two campaigns are analyzed, including negative and positive cloud‐to‐ground discharges and intracloud ones. The analysis outlines the method efficiency and the strong variability of lightning as sound sources in terms of both power spatial distribution and overall value. Lastly, the correlation of this later with electrical parameters is investigated, either peak current (provided by LLS) or Charge Moment Change, resulting from broadband Extremely Low Frequency (ELF) measurements.

Insight Discovery of the Roman Amphitheater of Durres: Reconstruction of the Acoustic Features to Its Original Shape

The discovery of Roman amphitheaters continues to excite the minds of archaeologists. Within the framework of various excavation campaigns, the architectural requalification of the amphitheater of Durres has been investigated, but no acoustic analyses have yet been carried out. This paper deals with the acoustic reconstruction of the Roman amphitheater of Durres in its original form. A campaign of acoustic measurements was carried out in accordance with ISO 3382 in order to understand the existing conditions, which are very detrimental to any type of live performance. After an accurate analysis of the geometric composition of the building, acoustic simulations were performed to determine the original acoustic response of the building. A comparison of the measured and simulated results, with and without an audience, was made in terms of the main acoustic parameters, while the acoustic map showing the spatial distribution of speech clarity at 1 kHz was added as an alternative way of representing the data. The outcomes show that the results related to the original shape are closer to the optimal values than the existing conditions.

Acoustic reconstruction of the vortex field in the nonuniform temperature field of a simulated furnace

The high-temperature thermal vortex flows generated by the tangential combustion of large-scale coal-fired power plant boilers represent a complex medium that causes acoustic ray bending. In this paper, nonlinear acoustic tomography is combined with particle swarm optimization as a means of reconstructing the two-dimensional thermal vortex field. The nonuniform and large-gradient temperature distribution is the main cause of acoustic ray bending. We establish curved paths of acoustic propagation that are closely related to the temperature distribution. Based on these curved paths, a set of radial basis functions combined with Tikhonov regularization is derived to achieve more accurate reconstruction of the temperature field. The nonuniform temperature field affects the reconstruction of the flow field information. Our model considers a variation in the angle between the direction vector of the acoustic curved paths and the horizontal and vertical components of the flow velocity, and incorporates a priori information and a six-parameter hypersurface into the flow field reconstruction scheme. Particle swarm optimization is applied to minimize the objective function and obtain the vortex velocity field. Numerical experiments show that the proposed mathematical model of acoustic ray bending improves the reconstruction accuracy of the temperature distribution and vortex flow field. The acoustic time-of-flight is experimentally measured through the generalized cross-correlation with different window functions. The temperature and vortex fields reconstructed based on the actual time-of-flight are compared with thermocouple and anemometer measurements to demonstrate the validity and robustness of the proposed reconstruction model.

An Acoustic Reconstruction of the House of Commons, c. 1820–1834

This paper presents an acoustic reconstruction of the UK House of Commons between c. 1820 and 1834. Focusing on a historically important site where political decisions were debated over the centuries, we aim to simulate and present the intangible principles of the acoustic properties and sounds heard within the space. The acoustic model was created based on available historical evidence with the aid of commercial acoustic simulation software. We discuss the decisions made for this reconstruction based on further experimentation with the acoustic characteristics of the constituent materials and settings of the available software. An additional comparison of the achieved acoustic results with spaces of similar historical importance and layout is presented, as a calibration of the model with in situ measurements was not possible in this case study. The values of T30, EDT, C50 and Ts are presented, while auralization examples are also available for a subjective evaluation of the results.

A sound from the arena: acoustic reconstruction of a Roman amphitheater located in Avella, south of Italy

In the ancient Rome the shows entertained by gladiators were very numerous, due to the always growing request from the spectators. After the disuse of the amphitheaters, a wide number of philosophers, writers and poets have been experienced to say what happened in these arenas. Nowadays this type of shows represents continuous source of inspiration for different books and movies (e.g. The gladiator, Spartacus). The amphitheaters are characterized by having an elliptical plan layout, which allow to enlarge the capacity of seats other than improving the sight from the steps of the cavea. The most famous Roman amphitheater is the Colosseum with its biggest dimensions that only the capital city of the empire could have, followed by others of smaller volume size. The development of Christianism decreed the immorality of these shows while the barbaric invasions contributed to convert these places into military barracks, if they were not selected to be demolished. This paper deals with the acoustic study of the amphitheater of Avella, which has been found only a few decades ago by archaeological excavations. The geometrical characteristics are typical of other amphitheaters built in Campania during the Imperial age. An acoustic survey has been undertaken in order to understand the main acoustic parameters in accordance with ISO 3382-1, given the functionality of this place in hosting musical shows during the summer seasons. Based on historical sources and discoveries, a virtual model has been realized to represent the architectural features of how the amphitheater would be looked like originally. The model has been used for acoustic simulations by applying the absorption and scattering coefficients of the finish materials, and the results have been assessed to highlight the different acoustic perception between the existing conditions and the original shape.

Optimal Sensor Positioning for the Sparse Measurement in the Acoustic Reconstruction of a Large Source

Near-field acoustic holography (NAH) has become an effective tool for acoustic source identification. It usually requires many microphones near the source surface to catch sufficient evanescent waves for good spatial resolution. Besides, such a measurement is time-consuming and uneconomical in practice; standard measurements using densely and uniformly populated sensors are sometimes impossible when dealing with massive sources. Eventually, the compressive sensing (CS) technique has been suggested for NAH, which employs a sparse number of sensors. Most existing works in NAH based on compressive sensing theory have focused on developing acoustic models and algorithms; In contrast, less attention has been paid to the best practice of sensor placement. The present study aims to propose and validate the methods for the optimal selection of sparse measuring points using the compression technique for NAH. Due to the small number of measuring sensors, the transfer matrix between source and hologram points becomes underdetermined. Under such a data condition, even though every piece of data would be felt precious for the reconstruction, the information from some sensors should be discarded further because not all data provide meaningfully independent information. To this end, effective independence and singular-value monitoring methods are used to test the selection of the optimal sensor position from a set of candidate positions. The former chooses non-redundant measurement data, whereas the latter keeps the low condition number of the transfer matrix. Simulation results with vibrating plates show that optimized sensor positions could effectively facilitate the optimality of the approximate solution for CS theory compared to uniformly or randomly distributed measurements. It is because the established transfer matrix has the lowest condition number due to being sparser and more independent sensor positions. Experimental results exhibit a better reconstruction error (10–40%) at 200–2,000 Hz when the sensor positions are optimized than the uniform or random selection approaches.

Research on acoustic reconstruction methods of the hull vibration based on the limited vibration monitor data

The prediction of hull vibration response is the basis for the quantitative control of cabin noise and underwater radiated noise, which has an important engineering value to obtain vibration characteristics accurately. In this paper, a new method is proposed to reconstruct hull vibration by some monitoring data in low frequencies. The hull vibration response is reconstructed by the monitoring data and the transfer function, and the ill-posed problem of inversion for the transfer function matrix is solved by the total least-squares regularization. A P-GRU (Peak-based Gated Recurrent Unit) neural network correction model is proposed to improve the prediction accuracy of vibration response. Taking a certain cabin structure as an example, some research such as the hull vibration data monitoring, the vibration transfer function calculation, vibration response reconstruction, and correction based on experimental data were carried out, and the simulation calculations and verification of experiment models were obtained. The multi-parameter comprehensive method is adopted to quantitatively evaluate the results between the simulation and the experiment. The results show that the acoustic reconstruction results are in good agreement with the experimental data. The overall level error is within 3 dB, the main peak value correlation coefficient is above 0.9, and the main peak difference is within 4 dB. The mechanism of the rapid and accurate prediction of the low-frequency vibration for the hull based on limited monitoring data is discussed by using a semi-physical simulation method combining the simulation calculation, vibration monitoring, and machine learning. The problem of phase asynchrony was solved, and strong support was provided for the construction of the ship's acoustic digital twin.

Virtual acoustic reconstruction of the Roman amphitheater of Avella in Italy

In ancient Rome, gladiator fights were very popular. The places where these shows took place were called amphitheaters, due to the particular shape of the elliptical building. Amphitheaters were widespread, and in each city, one or more of these buildings was present. This paper describes the virtual reconstruction of the acoustics of the amphitheater Avella, close to Naples, Italy. This amphitheater was discovered a few decades ago and was only partially rebuilt. Today, it is used for musical performances during the summer season mainly. The plan of the building is elliptical, and the dimensions of the arena are 35 m for the minor axis and 65 m for the major axis. Acoustic measurements were performed in the current state with an impulsive sound source and the acoustic parameters were obtained according to the ISO 3382 standard. Subsequently, from the dimensions of the current state and in analogy with the architecture of other amphitheaters existing today, a virtual reconstruction of the original shape was performed. The virtual model was developed with the architectural acoustics software Ramsete in order to obtain the acoustic characteristics of the amphitheater as it was in Roman times. In particular, the spatial distribution of the acoustic characteristics on the steps where the audience was seated is described and discussed.

Acoustic Hologram Reconstruction With Unsupervised Neural Network

An acoustic hologram is crucial in various acoustics applications. The reconstruction accuracy of the acoustic field from the hologram is important for determining the performance of the acoustic hologram system. However, challenges remain in acoustic hologram reconstruction where the conventional reconstruction methods generally lack accuracy, complexity, and flexibility. Although the deep learning (DL)–based method has been used to overcome these limitations, it needs the labeled training data to optimize the network with a supervised strategy. To address the problem, we put forward a new unsupervised DL-based reconstruction method in this work, termed PhysNet-AH, which is implemented by integrating a convolutional neural network with a physical model representing the process of acoustics hologram formation. The results demonstrate that we only need to provide PhysNet-AH with a single acoustic field recorded from the hologram, the network parameters can be optimized automatically without the labeled training data, and finally implement the acoustic hologram reconstruction with high accuracy, in terms of SSIM and mean squared error indicators. Furthermore, with the trained model, the robustness and generalization capability of PhysNet-AH have also been well-demonstrated by reconstructing the acoustic fields from different diffraction distances or different datasets. As a result, PhysNet-AH opens the door for fast, accurate, and flexible acoustic hologram–based applications.

Investigation of a Tuff Stone Church in Cappadocia via Acoustical Reconstruction

This study investigates the indoor acoustical characteristics of a Middle Byzantine masonry church in Cappadocia. The Bell Church is in partial ruins; therefore, archival data and the church’s remains are used for its acoustical reconstruction. The study aims to formulate a methodology for a realistic simulation of the church by testing the applicability of different approaches, including field and laboratory tests. By conducting qualitative and quantitative material tests, different tuff stone samples are examined from the region. Impedance tube tests are performed on the samples from Göreme and Ürgüp to document their sound absorption performances. Previous field tests on two sites in Cappadocia are also used to compare the sound absorption performance of tuff stones, supported by acoustical simulations. The texture, physical and chemical characteristics of the stones together with the measured sound absorption coefficient values are comparatively evaluated for selecting the most suitable material to be applied in the Bell Church simulations. The church was constructed in phases and underwent architectural modifications and additions over time. The indoor acoustical environment of the church is analyzed over objective acoustical parameters of EDT, T30, C50, C80, D50, and STI for its different phases with different architectural features and functional patterns.

A Review on Acoustic Reconstruction of Temperature Profiles: From Time Measurement to Reconstruction Algorithm

Acoustic tomography is a technique widely used in non-intrusive temperature measurement. Times of flight (TOF) of acoustic waves can be used to estimate temperatures of a measurement area. After obtaining TOF of some transmitter-receiver pairs, the temperature profile of the probed area can be estimated by some reconstruction algorithms. Temperature profiles play a critical role in the safe operation and efficient control of thermal-related mechanical systems. This article aims to present a systematic review on the acoustic reconstruction of the temperature profile, including TOF measurements and reconstruction algorithms. First, time-domain, Fourier-domain, and hybrid domain methods for the TOF measurement are revisited and discussed. Second, algorithms for the solution of the reconstruction model are reviewed from three groups of regularization methods. We also discuss how to choose the regularization parameter and to form a good preconditioner for fast calculation. Third, some extensions in TOF measurements and reconstruction methods and potential errors that may affect the acoustic reconstruction are also discussed. Finally, some applications are presented. A framework for the whole reconstruction process can be a useful resource to help researchers select a proper method for specific applications.

Cosmic birth: efficient Bayesian inference of the evolving cosmic web from galaxy surveys

ABSTRACT We present cosmic birth (COSMological Initial Conditions from Bayesian Inference Reconstructions with THeoretical models): an algorithm to reconstruct the primordial and evolved cosmic density fields from galaxy surveys on the light-cone. The displacement and peculiar velocity fields are obtained from forward modelling at different redshift snapshots given some initial cosmic density field within a Gibbs-sampling scheme. This allows us to map galaxies, observed in a light-cone, to a single high redshift and hereby provide tracers and the corresponding survey completeness in Lagrangian space including tetrahedral tessellation mapping. These Lagrangian tracers in turn permit us to efficiently obtain the primordial density field, making the cosmic birth code general to any structure formation model. Our tests are restricted for the time being to augmented Lagrangian perturbation theory. We show how to robustly compute the non-linear Lagrangian bias from clustering measurements in a numerical way, enabling us to get unbiased dark matter field reconstructions at initial cosmic times. We also show that we can accurately recover the information of the dark matter field from the galaxy distribution based on a detailed simulation. Novel key ingredients to this approach are a higher order Hamiltonian-sampling technique and a non-diagonal Hamiltonian mass matrix. This technique could be used to study the Eulerian galaxy bias from galaxy surveys and could become an ideal baryon acoustic reconstruction technique. In summary, this method represents a general reconstruction technique, including in a self-consistent way a survey mask, non-linear and non-local bias, and redshift-space distortions, with an efficiency about 10 times superior to previous comparable methods.

Virtual acoustic reconstruction of the Miners’ Theatre in Idrija (Slovenia)

This study reports history and the original architectural design of the Miners’ Theatre in Idrija. This theatre is usually considered to be the oldest such building in Slovenia and in 2001 it was declared a cultural monument of national importance. The building shape was typical of numerous small stand-alone theatres throughout Central Europe in the 18th century. The original design was later changed several times until it has reached the actual aspect. To analyse the acoustic characteristics of the current room (often named “Film Theatre”), an acoustic survey was carried out and several acoustic parameters defined in the ISO 3382-1 standard, were calculated and analysed. To study the acoustic characteristics of the theatre in its original shape, a numerical model was realized and properly validated. The simulations of three different scenarios were performed and the results obtained from the simulation have been analysed and commented.

A hybrid kernel function approach for acoustic reconstruction of temperature distribution

This paper utilizes a hybrid kernel method based on a cubic + exponential kernel to reconstruct the temperature field in a measurement area. In the experiments, we simulate the internal circumstance of a furnace in the measurement area with a heat source. It is based on measuring the acoustic travel time (ATT) between several pairs of ultrasonic transducers placed around the entire probed area. These ATT data, in turn, are related to temperature along the sound paths between any two transducers. The ATT data can then be used as input data after pre-processing by means of mean filtering, correction, and calibration. On this basis, three other different kernel functions are presented, and then a thermal map can be reconstructed with one of these kernel-based methods. Experimental results indicate that the hybrid kernel method (our proposed method) has a lower condition number and provides more detailed temperature information on the probed area, compared with the cubic kernel method, the Gaussian + cubic method, and the exponential kernel method.

Noise source identification of high-speed motion mechanism of textile equipment based on equivalent source method

In order to accurately identify the noise sources of high-end textile equipment and achieve noise control, this paper takes warp knitting machine as an example to accurately locate the main voice mechanism. Firstly, the stability and accuracy of traditional equivalent source method (TRESM) and Bayesian regularization criterion method for acoustic field reconstruction in different frequency bands are simulated and verified. Secondly, the accuracy of iterative reweighted least squares (IRLS) and steepest descent iteration equivalent source method (SDIESM) in medium- and high-frequency bands is verified. The results show that TRESM and Bayesian methods are suitable for the identification of medium- and low-frequency noise sources, and IRLS and SDIESM algorithms have better adaptability to complex sound fields. Bayesian method, IRLS and SDIESM algorithm can be used to identify the noise sources of broadband warp knitting machine. The main noise sources are spindle motor, pulling roller, spindle of loop forming mechanism and push rod of comb bar transverse mechanism, which provide theoretical support for active noise reduction of loom.

A Spatial Modeling Approach for Linguistic Object Data: Analyzing Dialect Sound Variations Across Great Britain

Dialect variation is of considerable interest in linguistics and other social sciences. However, traditionally it has been studied using proxies (transcriptions) rather than acoustic recordings directly. We introduce novel statistical techniques to analyze geolocalized speech recordings and to explore the spatial variation of pronunciations continuously over the region of interest, as opposed to traditional isoglosses, which provide a discrete partition of the region. Data of this type require an explicit modeling of the variation in the mean and the covariance. Usual Euclidean metrics are not appropriate, and we therefore introduce the concept of d-covariance, which allows consistent estimation both in space and at individual locations. We then propose spatial smoothing for these objects which accounts for the possibly nonconvex geometry of the domain of interest. We apply the proposed method to data from the spoken part of the British National Corpus, deposited at the British Library, London, and we produce maps of the dialect variation over Great Britain. In addition, the methods allow for acoustic reconstruction across the domain of interest, allowing researchers to listen to the statistical analysis. Supplementary materials for this article are available online.

Impact of the Acoustic Forcing Level on the Transfer Matrix of a Turbulent Swirling Combustor with and Without Flame

Thermoacoustic instabilities are a major issue for industrial and domestic burners. One possible framework to study these instabilities is to represent the system by a network of Dimensionless Acoustic Transfer Matrices (DATM) that link pressure and velocity fluctuations upstream and downstream each element of the network. In this article, the DATM coefficients of a turbulent swirling combustor are determined for a thermoacoustically stable configuration using harmonic acoustic forcing. Since the dynamics of the whole system is controlled by nonlinearities, the impact of the forcing level needs to be considered. The four DATM coefficients are thus measured for reactive operating conditions (premixed flame) and cold flow conditions for increasing acoustic excitation levels. The velocity level is controlled by a hot wire located inside the injector, in a region with a laminar top-hat velocity profile. The upstream and downstream specific acoustic impedances are also measured. Results for the acoustic response under cold flow conditions are first presented. In this case, the DATM coefficients are found to be independent of the forcing level except for the modulus of the coefficients linking the downstream velocity fluctuations to the upstream pressure and velocity fluctuations. This behavior is linked to the nonlinear response of the injector but is not entirely captured by the acoustic network model developed in this work. For reactive operating conditions, measurements indicate that all DATM coefficients depend on the forcing level to a certain extent. The Flame Describing Function, linking heat release rate fluctuations to velocity fluctuations, is used to reconstruct the transfer matrix through an acoustic network model. This network model accurately predicts the trend of the measured coefficients but the impact of the forcing level is not reproduced. Saturation for reactive operating conditions is shown to be not only related to the nonlinear flame response but also to the nonlinear injector dynamics. Finally, a data-driven reconstruction of the FDF using the acoustic network model along with the hot wire and microphone measurements is performed. This data-driven acoustic reconstruction is subsequently compared with the FDF determined with an optical technique.

Theatrical virtual acoustic rendering with head movement interaction

AbstractNowadays, the use of virtual reality/virtual acoustics (VR/VA) in archaeology for rendering lost buildings is an important topic in the cultural heritage field. Moreover, the addition of additional senses apart from the sight increases the feeling of immersion in virtual environments. The aim of this paper is to show the interaction work developed in a VA system, based on Unity and FMOD, the graphical and acoustical reconstruction of an ancient building and the development of a VR goggles with headphones to render 3D audio and video interactively. This system has been implemented to render auralizations in a binaural system and has been applied to the renderization of an old and lost theatre in València (Spain). The first building of theatre was built in the 16th century, and was rebuilt several times until the 18th century. The auralization of several theatrical excerpts of different Spanish authors of that time is also presented. The integrated system has been subjectively evaluated, obtaining very satisfactory results.