Hasil untuk "Acoustics in engineering. Acoustical engineering"

Ablitzer Frédéric

This paper introduces a method for identifying natural frequencies and damping ratios from a free vibration response induced by an impact, without requiring measurement of the excitation force. The approach combines the conceptual simplicity of peak-picking with the robustness of a multi-component time-domain model of the signal. Modal components are identified iteratively, based on spectral peaks selected by the user. The method is deliberately supervised, yet designed to remain accessible to non-expert users. A graphical interface provides intuitive control over the identification process and immediate feedback on the quality of the reconstructed signal, both in the time and frequency domains. The method is illustrated through experimental applications, demonstrating that natural frequencies and damping ratios can be extracted from simple, non-invasive measurements of the sound radiated by structures following an impact excitation. The robustness of the method to measurement noise and modal overlap is evaluated, and the identified parameters are shown to be consistent with those obtained from conventional FRF-based modal identification.

Deutsch Thomas, Falanga Luigi, Willmes Klaus et al.

Introduction: As the statistical distribution of hearing thresholds moves towards stronger hearing impairments with age, plausible simulations of its perceptual effects are useful for a variety of applications. Four software tools for the simulation of hearing loss, capable of generating audible output, were evaluated. An overview of the simulators is presented, their capabilities and significant signal processing steps are introduced. Methods: The perceptual evaluation focuses on the simulation of elevated hearing thresholds. Two listening experiments were conducted to assess how accurately the hearing loss simulators can reproduce target audiograms, i.e., elevated hearing thresholds when normal-hearing listeners are subjected to the simulation. Mild and moderate degrees of simulated hearing loss conditions were defined based on typical hearing thresholds of 70- and 80-year-olds. The complementary technical analysis addresses additional simulated consequences of cochlear hearing loss by investigating input-vs.-output level functions and spectral smearing effects. Results: Statistically significant differences between simulators were found: Good agreement with the target hearing thresholds was found for the simulator “WHIS" (deviations 0 to 6 dB), while the others showed deviations of varying degree (−29 to 7 dB). The created input-output functions proved to be suitable for demonstrating expansive dynamic range processing and explaining the listening experiment results.

Riedel Stefan, Frank Matthias, Zotter Franz

When localizing sound sources in natural or virtual environments, multisensory integration that combines auditory and visual cues is often involved. This study aims to determine the effect of (non-)individual head-related transfer functions (HRTFs) on sound source localization in the presence of visual cues. Participants (N = 16) were seated in a hemispherical loudspeaker arrangement, and their task was to indicate the perceived direction of pink-noise bursts. The conditions included localization of real loudspeakers and virtualized loudspeakers based on binaural rendering with (non-)individual HRTFs. The horizontal spacing of the visible loudspeakers was 30 degrees or larger and the vertical spacing was varied between 30 degrees and 15 degrees, to focus on vertical discrimination. The results of a static localization experiment (no head movements during playback) demonstrated an increased rate of vertical local confusions using non-individual binaural room impulse responses (BRIRs) of the KU100 dummy head compared to individual BRIRs. Dynamic auditory-visual localization with non-individual HRTFs suffered from vertical uncertainty and bias in the frontal area, where local confusion rates were consistent with the static experiment. In conclusion, the horizontal localization mapping of dynamic binaural rendering with non-individual HRTFs was comparable to real loudspeaker reproduction, while the vertical mapping was significantly impaired.

AllahTavakoli Yahya, Marquis-Favre Catherine, Ichchou Mohamed N. et al.

Vibrating composite panels are widely used in airplanes, vehicles, and high-speed trains, where noise comfort is required. Optimizing their design requires integrating psychoacoustic assessments alongside vibroacoustic analysis. The research presents a psychoacoustic framework to enhance the sound quality of composite panels while maintaining their structural efficiency. Hence, vibroacoustic models previously validated through vibroacoustic laboratory experiments for various composite panels subjected to mechanical and diffuse acoustic excitations, were used to synthesize the sounds radiated from the panels. The framework required to validate the models perceptually. This ensured the synthesized sounds were perceived by listeners as equivalent to the recorded ones. A psychoacoustic paired-comparison test between recorded and synthesized sounds was conducted to perceptually assess the modeling. Next, the sound quality of composite panel designs was investigated. Hence, synthesized sounds of designs were evaluated through another psychoacoustic test and a preference analysis. The preference analysis identified optimal designs, correlating preferences with psychoacoustic indices, like loudness, and mechanical properties such as stiffness-to-mass ratio and damping. This integrated approach ensures that the resulting designs enhance the sound quality and meet structural performance requirements.

Dumortier Florent, Kha Jamie, Karimi Mahmoud et al.

Modeling the sound radiated from underwater structures immersed in various environments is necessary in ocean acoustics and naval engineering. Typically, an underwater vibroacoustic system is composed of an elastic cylindrical shell that is radiated into an unbounded fluid domain. However, in contrast to deep oceans, for a shallow water environment, the influence of the sea surface and seabed can no longer by ignored. The significant fluid-structure interaction arising from the coupling at the boundary of the structure and surrounding fluid complicates the prediction of vibroacoustic behaviour. A sub-structuring technique based on the condensed transfer function (CTF) approach and reverse condensed transfer function (rCTF) approach has been proposed recently to tackle complex vibroacoustic problems by coupling/decoupling the necessary subsystems. Its potential is demonstrated in the present study through a two-dimensional case study to predict the sound radiation from an elastic structure of a cylindrical shell excited by a harmonic line force and immersed in a fluid domain of a perfect underwater acoustic waveguide, that is composed of an upper free surface and a lower rigid floor. The targeted model is obtained from a perfect underwater waveguide in which a water disk is subtracted from, and an excited shell is added in place of the water disk. The predictions of the proposed CTF-rCTF process are verified against analytical solutions for two different partitions of the global system and two types of condensation functions.

Hochbaum Felix, Hundt Tony, Fiebig André et al.

The assessment of sounds using psychoacoustic parameters is important in many areas. For the binaural case, it is not sufficiently clear how the characteristics of both ear signals have to be combined so that they best reflect the binaural percept. In the case of the auditory sensation of sharpness, this is particularly unclear due to limited empirical data on the perception of sharpness in dichotic listening conditions. To expand the empirical database and allow discussion on calculation methods for binaural sharpness and the derivation of representative metrics reflecting the binaural percept, two listening experiments were designed and conducted. The participants evaluated a series of signals for their sharpness, which were presented as real sound sources in an anechoic chamber via loudspeakers and as virtual sound sources via headphones from different sound source positions in the horizontal plane. Paired comparison and rating scale methods have been used to collect the data. Both experiments on sharpness revealed a tendency towards decreasing sharpness perception across all lateral positions. In contrast to maximum sharpness values of the ipsilateral side, arithmetic and quadratic averaging (mean and RMS values) of sharpness calculated according to the Aures method reflected the listening test results well and appear to be promising approaches for determining a binaural single value for most of the considered signals. Monaural signals and signals with several sound sources showed particular abnormalities in the listening test, some of which cannot be explained well.

Schalcher Stefan, Zellmann Christoph, Wunderli Jean-Marc et al.

The next-generation aircraft noise simulation tool sonAIR was developed for the precise prediction of single flights and for acoustic optimisation of noise abatement flight procedures. As the tool is also capable to calculate complex scenarios such as yearly air operations, it may be used for noise mapping. This study evaluates different versions of the sonAIR aircraft noise model, each employing distinct input data and calculation settings, in comparison to each version as well as to the current FLULA2 model as a representative best-practice model. The analysis focuses on annual aircraft noise scenarios at Geneva Airport for the year 2017. The calculations reveal that sonAIR’s physics-based ground effect model introduces more local variability, resulting in less smooth noise contours but expected increased accuracy, especially when incorporating detailed ground properties. On average, however, the two models yield equivalent results. Further, while accounting for buildings improves local noise estimations through incorporating shielding effects, this adds complexity and substantial computational effort, making it suitable for specific investigations but impractical for large-scale noise mapping. Finally, meteorological effects reduce noise exposure close to the airport during daytime due to acoustic shadow zones, but double computational time, further constraining large-scale applicability. Additional calculations at Geneva Airport for a different year, for two operational years at Zurich Airport and for a hypothetical, idealized airport confirm the generalizability of these findings. The current results thus suggest to use sonAIR with detailed ground properties for general noise mapping, but to consider buildings and meteorological effects in the calculations for specific cases only.

Marmel Frédéric, Cretagne Léo, Thuong Linh-Thao et al.

This paper reports on a project that quantified the effects of sonic boom exposure on human responses, in situations representative of the daily life of European citizens, to inform policy, and develop protection concepts for a new generation of supersonic commercial aircraft that should emit a reduced but perceivable boom while flying overland. Two reduced boom simulators were affixed to the bedroom windows of a house located on our university campus. The simulators were used to study indoor the participants’ responses to simulated “outdoor” booms. Testing took place in both the living room and kitchen because the booms caused different intensities of rattle noise in those two rooms. Participants performed cognitive and psychophysical tasks (Marmel et al. Acta Acust. 8 (2024) 1. https://doi.org/10.1051/aacus/2023063) and had mandatory rests. Questionnaires were used to assess the participants’ introspective judgment of the boom interference with the activities and how it could be linked to their noise sensitivity. In addition, the participants’ perception of the booms was studied via ratings of annoyance and pleasantness, and via loudness comparisons. The negative interference of the booms was greater during rest than during tasks and for booms with higher than lower levels. This was not directly reflected in the objective performance degradation reported in the reference cited above and thus contributes to a more complete picture of the influence of the sonic booms on humans. Moreover, booms were found to be annoying and unpleasant, even more so at a higher level and with the presence of rattle noise.

Schuck Moritz, Haselhoff Timo, Lawrence Bryce T. et al.

Urbanization has intensified the complexity of acoustic environments, necessitating a more comprehensive understanding to support urban acoustic planning for healthier living spaces. Traditional noise monitoring, primarily based on sound pressure level indices, is insufficient for capturing the full scope of these environments. This study investigates whether a diverse set of acoustic metrics can improve the characterization of acoustic environments and examines their stability across different land use types. We analyzed 1 year of time-series data from acoustic monitoring stations in Bochum, Germany, calculating psychoacoustic, ecoacoustic, and complex network indices. Our goals were to: (1) identify interdependencies among selected metrics, (2) uncover temporal patterns in acoustic measurements, and (3) relate them to their respective locations. Methods included correlation analysis, DBSCAN (Density-Based Spatial Clustering of Applications with Noise) clustering, principal component analysis, and descriptive statistics with diurnal aggregation. The findings demonstrate that acoustic indices of eight distinct dimensions, along with eight individual metrics, reveal crucial temporal, spatial variations of the acoustic environment and the interplay of individual sound sources overlooked by conventional sound pressure level (SPL) metrics. In particular, the study identifies the maximum Sharpness (Aures method), Link Density, the Bioacoustic Index, and the Amplitude Index as the most effective predictors of land use types, achieving the highest Adjusted Rand Index values (0.25, 0.17, 0.13, 0.13). Incorporating such indices into acoustic monitoring practices offers a refined, site-sensitive framework to identify more nuanced qualities of the acoustic environment, therefore, potentially laying the groundwork for targeted urban interventions that could promote health.

Harrison Jay, Archer-Boyd Alan W., Murphy Damian T.

This paper presents the results of objective tests to assess the insertion loss and gain performance of three true wireless earbuds that featured both active noise cancellation (ANC) and hear-through functionality. An acoustic test fixture (ATF) was used to examine the earbuds’ attenuation and boosting of broadband noise, linearity of performance for different presentation levels, and consistency of performance over time. The results show that devices are capable of a wide range of both attenuation and boosting, with hear-through modes providing significant levels of boosting in frequencies that are considered important to the intelligibility of speech. Furthermore, none of the hear-through modes tested were found to provide responses that suggested the devices were capable of providing full acoustic transparency. The results may also be useful for those seeking to produce models that replicate key aspects of insertion loss and gain performance in contemporary true wireless earbuds.

Mantel Maximilian, Stampka Katja, Sarradj Ennes

Rolling noise is the dominant source for railway vehicles at medium train speeds. In order to reduce the contribution radiated by the rail, this paper investigates how structural irregularities affect sound propagation by varying the superstructure properties along a ballasted track. The so-called disorder is therefore used to optimise the track decay rate (TDR) and thus achieve a lower mean square velocity of the rail. Track parameters included in the analysis are the pad stiffness, the sleeper mass and the sleeper spacing. Structure-borne sound propagation in the rail is computed using a fast finite-difference method. Both periodically repeating and stochastically distributed variations are considered for parameter variation along the track, with up to three parameters being varied simultaneously. The most promising variation schemes are identified with the help of parameter optimisation using the brute-force method. It has been shown that a high TDR over a wider frequency range and a lower TDR drop in the pinned-pinned frequency range can be achieved due to the presence of disorder. The study indicates that variations of the superstructure parameters along the track are a promising method in order to reduce track vibration levels.

Eggenschwiler Kurt, Jansohn Tilljan, Blau Matthias et al.

Residential perimeter blocks can shield traffic noise, but the acoustical quality may be sub-optimal in the inner courtyards. This study investigated how effective sound-absorbing facade surfaces and balcony soffits as well as an absorbing floor (lawn) influence the acoustical quality in inner courtyards. Room acoustical simulations were carried out for eight generic and two real-world models with very large numbers of transmission paths. Facades (reflecting, fully absorbing, partially absorbing), balcony soffits (reflecting, absorbing) and courtyard floor (reflecting, absorbing) were varied. A range of room acoustical parameters were evaluated, namely, reverberation time T20, early decay time EDT, strength G, speech transmission index STI, and Dietsch’s echo criterion EK. The simulations revealed that fully absorbing facades are an effective measure to improve the acoustical quality in inner courtyards, while partially absorbing facades result in smaller improvements. In fact, each additional storey of absorbing facades further improves the situation. In the case of non-absorbing facades, absorbing balcony soffits or an absorbing floor in the inner courtyard are not very effective as individual measures and may even increase disturbances due to echoes. The same holds true for situations with absorbing facades. Their feasibility should therefore be clarified for the individual situation in question.

Dabankah Emmanuel Manu, Totaro Nicolas, Colangeli Claudio et al.

In acoustics, field reconstruction methods aim at retrieving acoustic fields (pressure, velocity and intensity) from acoustic measurements around a radiating source, which is often a vibrating structure of complex shape (pumps, engines…). If they are extensively used in laboratory conditions, their application to in situ characterization is not straightforward due to the presence of disturbing sources or masking objects, or to non-anechoic environments. The inverse Patch Transfer Function (iPTF) approach, thanks to the concept of virtual acoustic volume modelled by a finite element model, has already demonstrated its ability to deal with sources of complex shape and the presence of disturbing stationary sources in a non-anechoic acoustic environment. The objective of this article is to show how the presence of rigid masking objects can be easily and efficiently taken into account. A numerical experiment consisting of a thin, simply supported rectangular plate radiating noise in a semi-infinite acoustic field and partially masked by a rigid parallelepiped is presented. The acoustic fields identified and the directivity diagrams are compared with the reference and show that iPTF is able to cancel the presence of the masking object even if the latter completely covers the radiating plate. Finally, an industrial example consisting in an electric motor in operation is presented. Two configurations were tested: with and without the presence of a rigid object. Comparison of the results shows that the fields identified are in good agreement, demonstrating the ability of iPTF to cancel out the effect of masking objects.

Hölter Arne, Weinzierl Stefan, Lemke Mathias

In comparison to geometric acoustics, wave-based simulation techniques in the time domain have a much higher degree of accuracy. Latest modeling techniques like immersed boundaries reduce modeling effort significantly. This paper aims to present and discuss the use of techniques for first-order partial differential (non-linear) Euler equations in finite-difference time-domain simulations for room acoustic applications. This includes the governing equations, spatial and temporal discretization schemes, filtering schemes, and boundary conditions. All methods are fully parallelizable and mostly known from computational aeroacoustics. They are analyzed with respect to their dispersion and stability behavior as well as their computational efficiency. They are proven in a cubic room with rigid boundaries. Finally, a volume penalization method is used to mimic real impedance boundary conditions in benchmark cases for room acoustic simulations to demonstrate the transferability to real-world scenarios.

Bresciani Andrea P. C., Maillard Julien, Finez Arthur

This work presents the application and validation of a novel auralization approach for the evaluation of wind turbine noise annoyance under diverse conditions. The approach is based on the decomposition of each turbine blade into elementary short-segment sources, whose acoustic radiation in the far field is obtained by coupling Amiet’s emission model with the Harmonoise engineering model for outdoor sound propagation. The transfer functions between the elementary source positions and receivers are obtained. Then, the average and instantaneous sound pressure levels are calculated over one blade rotation. The realism of the audio signals is evaluated through listening tests with audio signals of the real and simulated environments. The predicted noise spectra from five wind turbines capture well the measured trends and the absolute levels. Finally, we present a study of the weather effects on noise emissions and propagation by using the numerical model developed.

Gondrum Miro, Satcunanathan Sutharsan, Niemöller Ansgar et al.

The accuracy of two direct coupled two-step CFD/CAA methods is discussed. For the flow field either a finite-volume (FV) method for the solution of the Navier–Stokes equations or a lattice Boltzmann (LB) method is coupled to a discontinuous Galerkin (DG) method for the solution of the acoustic perturbation equations. The coupling takes advantage of a joint Cartesian mesh allowing for the exchange of the acoustic sources without MPI communication. An immersed boundary treatment of the acoustic scattering from solid bodies by a novel solid wall formulation is implemented and validated in the DG method. Results for the case of a spinning vortex pair and the low Reynolds number unsteady flow around a circular cylinder show that a solution with comparable accuracy is obtained for the two direct-hybrid methods when using identical mesh resolution.

Gao Guochao, Cristini Paul, Favretto-Cristini Nathalie et al.

This work reports on some results obtained from numerical simulations of time-domain acoustic wave propagation in the presence of a periodically rough interface. Emphasis is put on the structure of the reflected signals in the presence of a sinusoidal grating. More specifically, we investigate the effect of the frequency bandwidth of the emitted signal and the effect of the incident wavefront sphericity on the signals reflected from the rough interface and associated with the different diffraction orders.

Gning Paul, Lanfranchi Vincent, Dauchez Nicolas

High voltage devices such as dry-type air-core reactors are subjected to environmental noise standards. Their excitation is due to Lorentz forces originated from the magnetic field, created by the coil itself, combined with the feed current. The objective of this paper is to show how spectral components present in the supply current of industrial dry-type air-core reactors is likely to produce a significant acoustic radiation. First, the multi-component distribution of the Lorentz forces is established. Then, the multi-physics computation process allowing to determine the acoustic pressure induced by each force component is presented. Finally, two industrial reactors are studied: a single and a multi-layer coil. It is pointed out that significant acoustic emergence can be induced by the interaction between small current spectral components with the fundamental or with each other.

Brauchler Alexander, Ziegler Pascal, Eberhard Peter

In this article, the transient motion of a realistically plucked guitar string is studied experimentally and numerically in both transversal polarizations. The frequency dependent damping and suitable initial conditions are identified in the experiment and used in a simulation. For this reason an experimental set-up consisting of a string, an excitation mechanism and two laser Doppler vibrometers is developed. The excitation mechanism performs a realistic and reproducible plucking motion with a plectrum. Two laser Doppler vibrometers are used to measure the string oscillation transversally in two polarizations. The experimental set-up makes it possible to measure the string’s motion under reproducible conditions and, hence, at different positions for the same oscillation. This capability renders the identification of suitable initial conditions, i.e., initial displacement and velocity as well as the pre-tension, for a string model possible. Furthermore, a finite element model for the string is developed that takes into account the oscillation in both transversal planes of polarization and the coupling between them. Finally, the model results are in good agreement with the measurements. With help of the numerical model it can be vividly shown that the coupling between the polarizations of the oscillation is due to a torsional movement of the string on the saddle.

A. Śliwiński

Professor Robert A. Mertens a creator of the scientific school of acousto-optics in Belgium passed away at home in Antwerpen on 7-th May 2006, 9 days after his 85-th birthday anniversary. He studied mathematics and theoretical physics at the University of Gent and graduated in 1943 (MSc), completed his PhD in 1949 and his DSc (Habilitation) in 1955. After several research positions at the Belgian Interuniversitary Institute of Nuclear Physics and the Belgian National Foundation he became Professor of Theoretical Mechanics at the Faculties of Sciences and Engineering of the University of Gent in 1963. He retired in 1986. He was a member of the Belgian Royal Academy of Sciences and the president of this Academy for 1992. He was a member of European Acoustics Association, a fellow of the Acoustical Society of America and participated in other numerous international scientific organizations. Professor Mertens' scientific interests focused on physical acoustics (theory of the interaction of the piano string and hammer, theoretical acousto-optics), transport theory and theoretical mechanics (nonlinear mechanics, adiabatic invariants, tops) and in the last few years on quantum mechanics (in relation to the Kapitza-Dirac effect and its analogy with acousto-optical interaction).