Acoustic Intensity Measurement of the Sound Field Radiated by a Concert Harp

Abstract An experimental study of the acoustic radiation of a concert harp is presented. Using a stationary mechanical excitation placed at one string location, the acoustic radiation of the complete instrument is investigated. Two main acoustic radiation sources are identified: the soundboard and the soundbox holes. Acoustic intensity vectors are measured in two planes located in the near field of these two sources, making use of a 3D intensity probe. A detailed description of the acoustic intensity field radiated by these two sources is given. Calculations of acoustic power radiated by the soundboard surface and by the soundbox holes allow us to quantify the relative importance of these two sources. In three frequency ranges, it is shown that the soundbox holes radiate more than the soundboard. In the first range, it is suggested that the acoustic radiation of the instrument can be described by two point sources of sound implying that in this range the harp acts as an equivalent elastic Helmholtz resonator

Validity of the One-Dimensional Limp Model for Porous Media

A straightforward criterion for determining the validity ofthe limp model validity for porous materials is addressed here. The limp model is an “equivalent fluid” model which gives a better description of porous behavior than the well known “rigid frame” model. It is derived from the poroelastic Biot model, assuming that the frame has no bulk stiffness. A criterion is proposed for identifying the porous materials for which the limp model can be used. It relies on a new parameter, the Frame Stiffness Influence FSI, based on porous material properties. The critical values of FSI under which the limp model can be used are determined using 1D analytical modeling for a specific boundary set: radiation of a vibrating plate covered by a porous layer.

How reproducible are methods to measure the dynamic viscoelastic properties of poroelastic media?

There is a considerable number of research publications on the acoustical properties of porous media with an elastic frame. A simple search through the Web of Science™ (last accessed 21 March 2018) suggests that there are at least 819 publications which deal with the acoustics of poroelastic media. A majority of these researches require accurate knowledge of the elastic properties over a broad frequency range. However, the accuracy of the measurement of the dynamic elastic properties of poroelastic media has been a contentious issue. The novelty of this paper is that it studies the reproducibility of some popular experimental methods which are used routinely to measure the key elastic properties such as the dynamic Young's modulus, loss factor and Poisson ratio of poroelastic media. In this paper, fourteen independent sets of laboratory measurements were performed on specimens of the same porous materials. The results from these measurements suggest that the reproducibility of this type of experimental method is poor. This work can be helpful to suggest improvements which can be developed to harmonize the way the elastic properties of poroelastic media are measured worldwide

Qualité des archets de violons et instabilité de type flambement

Les archets modernes haut de gamme sont fabriqués dans un bois exotique, le pernambouc. Le coût et la rareté de cette essence font qu'un matériau de substitution est actuellement recherché. L'objectif des travaux présentés est de déterminer les critères objectifs permettant de juger de la qualité d'un archet, de sorte que toute modification de matériau ou de géométrie pourra se faire en visant ces critères. Des essais en jeu (spiccato, attaque, notes longues, etc.) effectués sur huit archets sont corrélés à des mesures physiques (géométrie de la baguette, centre de gravité, raideur de la baguette, modes vibratoires, etc.). L'influence de plusieurs facteurs est mise en relief : la position du centre d'inertie, la tension du crin, la raideur de la baguette et sa stabilité au sens du flambement. Une méthode permettant d'estimer la force critique de flambement est proposée : sa corrélation avec la qualité des archets semble se dessiner

Validity of the One-Dimensional Limp Model for Porous Media

A straightforward criterion for determining the validity ofthe limp model validity for porous materials is addressed here. The limp model is an “equivalent fluid” model which gives a better description of porous behavior than the well known “rigid frame” model. It is derived from the poroelastic Biot model, assuming that the frame has no bulk stiffness. A criterion is proposed for identifying the porous materials for which the limp model can be used. It relies on a new parameter, the Frame Stiffness Influence FSI, based on porous material properties. The critical values of FSI under which the limp model can be used are determined using 1D analytical modeling for a specific boundary set: radiation of a vibrating plate covered by a porous layer.

Mesoscopic Rigid Body Modelling of the Extracellular Matrix Self-Assembly

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