A method to estimate the rectangular orthotropic plate elastic constants using least-squares and Chladni patterns

A method to retrieve the elastic constants of rectangular wooden plates is presented, relying on the measurement of a set of eigenfrequencies and the identification of the corresponding mode shapes, and belonging to the more general category of non-destructive inverse parameter estimation methods. Compared to previous works, the current method is effective with any choice of boundary conditions. Furthermore, the error function is linear in the elastic constants, which are computed via a matrix inversion. This framework lends itself naturally to a physical interpretation of the results in terms of linear combinations of eigenmodes, yielding new sets of modes and associated combined mode shapes in which the elastic constants are completely uncoupled. A number of numerical benchmark tests and experimental cases are treated in detail, highlighting the reliability of the proposed methodology in cases of interest in acoustics and musical acoustics.Comment: 22 pages, 12 figure

Experimentally-tuned Synthesis Of A Thin Plate

The numerical simulation of acoustic instruments and devices is a growing subject of research. Applications range from model-aided instrument making, to virtual instrument and effect design, to virtual reality applications. A faithful reproduction of the underlying system may be realised via signal-based analysis and resynthesis, starting usually from a recorded sample. Model-based synthesis, on the other hand, allows to reproduce the dynamics of common objects such as strings, bars and plates by setting a few physically meaningful parameters feeding a mathematical model. The latter allows far greater flexibility in terms of control and design, but often lacks the realism of the former. This work investigates the possibility of tuning a physical model using experimental data. The system considered here is a cantilever metal plate struck with a hammer. The physical model is derived from a modal decomposition of the Kirchhoff plate equation. A preliminary estimate of the unknown plate's rigidity constant is carried out first, via the measurement of the first eigenfrequency. Then, the finite difference scheme is used to solve the eigenvalue problem over a fine grid with the computed rigidity constant, and the modal shapes are then stored along with the modal frequencies. Experimental data are collected from a laboratory experiment, and a comparison of the experimental frequencies against the model's eigenfrequencies is carried out. The modal equations obtained from the difference scheme are then adjusted to compensate for the errors in the eigenfrequencies. Experimental decay times are also implemented in the scheme. Tuned numerical impulse responses at three different combinations of input and output locations are then computed and compared to the experimental responses, showing a high degree of accuracy

FAST ESTIMATION OF WOOD ELASTIC CONSTANTS USING LEAST-SQUARES

Mechanical properties of materials represent, among others, one of the most relevant topics in musical acoustics. Such features can be used to better understand the behaviour of musical instruments or to evaluate the impact of design interventions, and build accurate physical models. In this regard, this paper aims to introduce an accessible procedure to estimate the elastic constants of wood using a thin plate. Compared to previous methods in the literature, the inverse problem is here formulated linearly in the rigidity constants, thus allowing a unique solution via a matrix inverse, and using a least-squares formulation. The reliability of the method is numerically proven in a number of examples

Loudspeaker analysis : a radar based approach

Recently radar based micro-Doppler signature analysis has been successfully applied in various sectors including defence, biomedical and automotive. This paper presents the novel use of radar micro-Doppler for loudspeaker analysis. The approach offers the potential benefits of characterising the mechanical motion of a loudspeaker in order to identify defects and design issues. Compared to acoustic based approaches, the use of a radar allows reliable measurements in an acoustically noisy end of production line. In addition, when compared witha laser vibrometric approach the use of radar micro-Doppler reduces the number of measurements required and provides direct access to the information of the metallic components of the loudspeaker. In the paper experimental results and analysis of the micro-Doppler signatures of loudspeakers using low cost radar systems are presented. Based on Thiele&Small parameters, the voice coil displacement is modelled and micro-Doppler signatures for a single tone and a sine sweep stimulus are presented. Furthermore, in order to characterise the speaker with a single radar measurement, a methodology to measure mechanical frequency response of loudspeakers is also shown

Partitioned block frequency domain prediction error method based acoustic feedback cancellation for long feedback path

In this paper an innovative method of using Acoustic Feedback Cancellation (PEM based PBFD-AFC) in large acoustic spaces is presented. The system under analysis could vary from Single Source Single Receiver (SISR) to a Multiple Sources Multiple Receivers (MSMR). An environment is representative of (e.g.) churches installations or Public Address (PA) systems, thus involving the presence of one or more microphones and corresponding feedback paths. The Partitioned Block approach consists of slicing the feedback path (e.g the impulse response of the system) to improve the algorithm performance. It can be applied either in the time domain or in the frequency domain, where the latter, called Partitioned Block Frequency Domain, shows faster convergence, lower computational cost and higher estimation accuracy. The results of the proposed framework is compared with the state of the art using real acoustic data showing superior performance with up to 20dB Maximum Stable Gain (MSG) and 30 seconds less convergence time

Identification of Soft Tissue-Mimicking Materials and Application in the Characterization of Sensors for Lung Sounds

Early diagnosis of pulmonary implications is fundamental for the treatment of several diseases, such as idiopathic pulmonary fibrosis, rheumatoid arthritis, connective tissue diseases and interstitial pneumonia secondary to COVID-19 among the many. Recent studies prove that a wide class of pulmonary diseases can be early detected by auscultation and suitably developed algorithms for the analysis of lung sounds. Indeed, the technical characteristics of sensors have an impact on the quality of the acquired lung sounds. The availability of a fair and quantitative approach to sensors’ comparison is a prerequisite for the development of new diagnostic tools. In this work the problem of a fair comparison between sensors for lung sounds is decoupled into two steps. The first part of this study is devoted to the identification of a synthetic material capable of mimicking the acoustic behavior of human soft tissues; this material is then adopted as a reference. In the second part, the standard skin is exploited to quantitatively compare several types of sensors in terms of noise floor and sensitivity. The proposed methodology leads to reproducible results and allows to consider sensors of different nature, e.g. laryngophone, electret microphone, digital MEMS microphone, mechanical phonendoscope and electronic phonendoscope. Finally, the experimental results are interpreted under the new perspective of equivalent sensitivity and some important guidelines for the design of new sensors are provided. These guidelines could represent the starting point for improving the devices for acquisition of lung sounds