The bulk-boundary correspondence, which relates topological properties of a material in the bulk to the presence of robust modes localized on the edge, is at the core of the now mature field of topological wave physics. More recently, it was realized that in crystalline structures, certain types of defects can host localized modes, in which case the bulk-boundary correspondence has to be replaced by a bulk-defect correspondence. These defect-localized modes are expected to have robust properties owing to their topological origin. In this work, we show how to obtain topological defect modes in a lattice possessing both mirror and chiral symmetry. The defect is obtained by endowing a plaquette with a non-trivial gauge flux. We show that the bulk-defect correspondence is satisfied by introducing appropriate topological invariants. Moreover, the topological defect modes are shown to be highly robust to the introduction of symmetry-preserving disorder. The model is then realized in an acoustic system made of a bilayer network of tubes, and the presence of topological defect modes is experimentally clearly demonstrated.

The first published attempt to measure human voice directivity in 1929 involved a single microphone and a rotating chair.Since then, a number of experiments were conducted, increasing the level of detail of the sound field representation according to the available equipment.Most experiments assumed repeatability of voice production by the human talker over an iterative process, which can hardly be guaranteed even for trained subjects.Hence using a rotating device to retrieve the 3D directivity of a human talker is questioned.All measurement positions should preferably be recorded simultaneously to ensure an optimal consistency of the obtained directivity patterns.The present experimental setup is composed of 256 MEMS microphones located on a spherical structure of 1.80 m radius.The characteristics (sensitivity, frequency range, and dynamics) of those compact devices are presented and allow for measurements of voice directivity from 50 Hz up to 20 kHz.A first step of characterization is conducted with a reproducible sound source composed of 12 Aurasound loudspeakers producing controlled directivity.Then, human talkers are recorded in the system.Far-field directivity functions are estimated using a spherical wave propagation model.The obtained results are consistent with the previous literature and provide an extended angular accuracy.

The far-field directivity function (FFDF) of a sound source characterises the angular dependence of the acoustic fields far away from this source. This function can be estimated by performing a spherical wave expansion (SWE) of the sound field from pressure measurements distributed around the source. The truncation order of the SWE is a critical parameter that depends on the number of measurement points and on the spatial sampling scheme used for the measurements. Unfortunately, for irregular sampling schemes, no theoretical result allows to determine a truncation order. In this work, a surrounding cuboid microphone array composed of 256 MEMS microphones is deployed. A cross-validation framework is used in order to determine an optimal truncation order for the SWE of the field radiated by a test source. The quality of the reconstructed field is assessed on the frequency range 100-5000 Hz. Finally, the estimated SWEs and far-field directivities are compared to an analytical model of the test source.

The reproduction of the vibration and acoustic responses of structures under random excitation such as the diffuse acoustic field or the turbulent boundary layer is of particular interest to researchers and the transportation industry (automobile, aeronautics, etc.). In practice, the characterization of structures under random excitations requires making in-situ measurements or using test facilities such as the wind tunnel, which are complex and costly methods. Based on the previous considerations, the necessity of finding simple, cost-efficient and reproducible alternative methods becomes obvious. The source scanning technique based on a single acoustic source and the synthetic array principle is one of these alternative techniques. The present paper proposes to assess its validity by comparing its results with numerical and experimental ones. An academic case study consisting of a baffled and simply supported aluminum panel under diffuse acoustic field and turbulent boundary layer excitations is considered. The experimental vibration response of the panel as well as the transmission loss using the proposed process are compared to results from random vibration theory on one hand. On the other hand, the same experimental results obtained using the source scanning technique are compared with results obtained with measurements using a reverberant room (diffuse acoustic field) and an anechoic wind tunnel (turbulent boundary layer). These comparisons show good agreement that validate the source scanning technique for the considered panel.

The experimental study of a structure’s response to a turbulent boundary layer (TBL) excitation using wind-tunnel or in-vehicle testing generally requires considerable efforts, including the measurement of both turbulent wall-pressure fluctuations and the structure’s vibration response. As an alternative method to highly demanding testing procedures and numerical simulations, this paper proposes a computationally efficient method to predict vibroacoustic responses of a panel under a TBL excitation. Space-time realizations of a TBL wall pressure field obtained using a spectral synthesis approach are coupled to a deterministic model so as to predict mean quadratic velocity, and radiated sound pressure and power from a panel under a TBL excitation. Each realization of the wall pressure field and obtained vibroacoustic results can be considered as a virtual experiment. The radiated sound pressure as a function of time can be also obtained, and possibly later used for listening and psychoacoustics studies objectives. A summary of existing experimental and numerical methods for obtaining the vibroacoustic response of panels to a TBL excitation is first presented. The proposed method is then detailed. Results obtained using this method are finally compared to results obtained using controlled laboratory experiments and analytical calculations for a low subsonic flow speed.

Woodwind tonehole's linear behavior is characterized by two complex quantities: the series and shunt acoustic impedances. A method to determine experimentally these two quantities is presented for the case of open toneholes. It is based on two input impedance measurements. The method can be applied to clarinet-like instruments, and can be used for undercut toneholes as well as toneholes with pads above their output, under the condition that a symmetry axis exists. The robustness of the method proposed is explored numerically through the simulation of the experiment when considering geometrical and measurement uncertainties. Experimental results confirm the relevance of the method proposed to estimate the shunt impedance. Even the effect of small changes in the hole's geometry, such as those induced by undercutting, are characterized experimentally. The main effect of undercutting is shown to be a decrease in the tonehole's acoustic mass, in agreement with theoretical considerations based on the shape of the tonehole. Investigation on the effects of pads will be studied in a further work. Experimental results also reveal that losses in toneholes are significantly higher than those predicted by the theory. Therefore, the method is suitable for the experimental determination of the shunt impedance, but it is not convenient for the characterization of the series impedance.

In woodwind instruments, lateral holes or toneholes, are used to reduce the effective length of the instrument in order to increase the number of notes that can be played. Over the time, instrument makers have noticed that details of the tonehole’s geometry play a major role in the musical quality of woodwind instruments, a change in geometry impacts parameters such as: tuning, volume, and timbre. From the scientific point of view, it is of interest to link the tonehole’s geometry to the acoustical properties of the produced sound. A single tonehole can be represented by a lumped T circuit comprised of a shunt and series impedance. In order to determine the values of these impedances, several methods have been developped, Keefe [1], Nederveen [2], Dubos et al. [3], Dalmont et al. [4], Dickens [5], Lefebvre and Scavone [6], these include theoretical, experimental, and numerical approaches. In this study a new method is proposed and compared to the method developed by Dalmont et al. [4]. The new approach is based on two measurements of the input impedance instead of the measurement of the input and transfer impedances of the method proposed by Dalmont et al. Also the tonehole position does not need to be at the middle of the main tube. Simulations of the experiments of both methods were performed to compare the effect of the uncertainty over the accuracy of the results. These results can be used for the design, and improvement of woodwind instruments.

The reproduction of the vibration and acoustic responses of structures under random excitation such as the diffuse acoustic field or the turbulent boundary layer is of particular interest to researchers and the transportation industry (automobile, aeronautics, etc.) as well. Indeed, the determination of these vibroacoustic responses requires making in-situ measurements or using test facilities such as the anechoic wind tunnel, which are complex and costly methods. Another drawback of these test means is the variability of the results when for instance; the same structure is tested in different facilities of the same kind. Based on the previous considerations, the necessity of finding a simple, cost-efficient and reproducible alternative method becomes obvious. In the present paper, a method of achieving this goal using a single acoustic source and the synthetic array principle is proposed. To assess the validity of this method, we propose an academic case study consisting of a baffled and simply supported aluminum panel under diffuse acoustic field and turbulent boundary layer excitations. The vibration response of the plate as well as the transmission loss are determined with the proposed process and compared to results from random vibration theory. These comparisons show good agreement between both the results obtained with the proposed approach and the theoretical ones.

In the framework of the VIRTECH ANR project, alternative experimental methods are developed to replace or complement the use of large and costly facilities (rever-berant room, wind tunnel) for the vibro-acoustic charac-terization of structures under random excitations (Diffuse Acoustic Field - DAF, Turbulent Boundary Layer - TBL, respectively). In the case of TBL excitation, numerical methods are investigated to replace Computational Flow Dynamics (CFD) methods that are computationally costly, even when flat panels without obstacle nor pressure gra-dient are considered. In that context, this work presents a space-time (2D+t) synthesis approach to efficiently syn-thetize a wall pressure field that can be coupled to a deterministic vibration model of the structure. Any model of wall pressure field (autospectra, correlation length) can be used to set up the synthesis approach to represent random excitations like DAF or TBL. The pressure field radiated by the panel can even be obtained in the time domain, and be used for sound perception purposes to evaluate the vari-ations linked to the damping of the structure, the empirical model used for the synthesis (eg. Corcos, Mellen) or the probability density functions of the wall pressure excitation (Gaussian or non Gaussian). In the present work, a deterministic finite element model of a stiffened panel is coupled to 2D+t stationary wall pressure fields to obtain its vibroacoustic response under DAF and TBL excitations in the frequency domain.

Finding an alternative to common test means (reverberant chamber, wind tunnel facilities, in-situ measurements, etc.) is of particular interest to the transportation industry (automobile, aeronautics , etc.) for the reproduction of the vibroacoustic response of structures under random excitations such as the diffuse acoustic field or the turbulent boundary layer. In this paper a method of achieving this goal using a single acoustic source and the synthetic array principle is proposed. To assess the validity of this method, an academic case study consisting of a simply supported thin aluminum plate under turbulent boundary layer excitation is presented. The vibroacoustic response of the plate is determined with the proposed process and compared to results from random vibration theory and direct measurements in an anechoic wind tunnel facility. This comparison shows good agreement between the proposed approach and both the theoretical and wind tunnel results.

Groupe d’acoustique de l’université de Sherbrooke, Facult de génie, Dépt. de génie mécanique, 2500, boulevard de l’université, Sherbrooke, J1K2R1, Canada e-mail: olivier.robin@usherbrooke.ca, alain.berry@usherbrooke.ca Laboratoire de mécanique et d’acoustique, 4, impasse Nikola Tesla, 13453 Marseille, France e-mail: pachebat@lma.cnrs-mrs.fr Univ Lyon, INSA-Lyon, Laboratoire Vibrations Acoustique, F69621 Villeurbanne, France e-mail: nicolas.totaro@insa-lyon.fr