Son (physique) | EPFL Graph Search

vignette|upright=1|Propagation d'ondes sphériques de pression dans un fluide. Le son est une vibration mécanique d'un fluide, qui se propage sous forme dondes longitudinales grâce à la déformation élastique de ce fluide. Les êtres humains, comme beaucoup d'animaux, ressentent cette vibration grâce au sens de l'ouïe. L'acoustique est la science qui étudie les sons ; la psychoacoustique étudie la manière dont les organes du corps humain ressentent et l'être humain perçoit et interprète les sons. Émission Toute vibration d'un milieu fluide peut être considérée comme un son si son énergie est notable dans le domaine des fréquences audibles par l'homme (−), et par extension s'il l'est dans celui des infrasons () ou des ultrasons (−). Tout phénomène capable d'engendrer des vibrations dans un fluide peut éventuellement émettre un son. Le phénomène initial n'est pas nécessairement vibratoire : une surpression temporaire (due par exemple à une explosion) ou une dépression (due pa

Scale Model Evaluation and Optimization of Sodar Acoustic Baffles

Adrien Chabbey, Fernando Porté Agel

A 21: 1 scaled sodar, operating at 40 kHz, has been built and tested in the laboratory. Sodars, which use sound scattered by turbulence to profile the lowest few hundred meters of the atmosphere, need good acoustic shielding to diminish annoyance and to reduce unwanted reflections from nearby objects. Design of the acoustic shielding is generally inhibited by the difficulty of testing on full-scale systems and uncertainty as to accuracy of models. In contrast, the scale model approach described allows for "bench testing" of many designs under controlled conditions, and efficient comparison with models. Measured beam patterns from the scale model were compared with those from a numerical model based on the Kirchhoff integral theorem. Satisfactory agreement has allowed using the numerical model to optimize the acoustic shield design, both for the gross acoustic baffle geometry and for the geometry of rim modulations known as thnadners. Optimization was performed in the specific case of a scaled model of a commercial phased array sodar.

American Meteorological Society2015

Conception acoustique de systèmes microtechniques

Jean-Daniel Lüthi

Considered as one of the most difficult complications in horology, the mechanical chiming watch, known as the striking watch, has today become one of the symbols of high craftsmanship. When it chimes the hour the sound of a striking watch must not only be harmonious to the ear of the hearer but also be identical from one watch to another. Today only a few talented watchmakers produce these watches. The resulting empiricism sometimes translates into significant differences between the sounds of these watches. One particularly complex aspect in the application of sound to a striking watch is the appreciation of the sound quality as well as the adequacy to the sound reference. This thesis aims to identify the principal influencing factors at the origin of the variances in sound from one striking watch to another and to identify those that allow the sound of one watch to conform to a recognised ideal sound. The problem is approached from two different angles. The first angle of physical reality, attempts to describe and characterise the sound produced by a watch according to physical parameters. The second angle of perceptive reality models our perception of sound. A virtual spectrum can be established by taking into account psychoacoustic aspects. This is derived from the real spectrum and allows not only a quantified measure of the perceived pitch but also an appreciation of the tone quality. The experimental work relies on the implementation of designed experiments using a functional sample. This reproduces the striking system at the same time allowing the modification of parameters necessary for the planned experiments. The physical spectrum combined with the virtual spectrum allows the identification of the principal influencing factors. Amongst these are hammer-gong pre-penetration, the contact geometry as well as the position of the hitting point and the contact time. By means of the generalised mass, it is possible to modify the perceived pitch within a significant range of frequencies which makes this factor an important element in the adequacy to the recognised ideal of sound. Finally, this work illustrates the importance that should be accorded to the implementation of measuring tools and appropriate characterisation of sound if the processes in the mechanical striking watch industry are to be mastered. Also included is a description of the factors that the watchmaker must control to ensure minimal variation from one watch to another in a production series.

EPFL2011

A sound diffusion system for directional sound enhancement

Baptiste Crettaz, Alexandre Delidais, Alain Dufaux, Xavier Falourd, Hervé Lissek, Patrick Marmaroli, Cédric Monchâtre

A loudspeaker array is described including several circular sound emitters that are bunked. One circular sound emitter can be either a circular array of loudspeakers (kind 1) or a toroidal loudspeaker (kind 2). The loudspeaker array can be composed of circular sound emitters of kind 1, kind 2 or both.A toroidal loudspeaker is a loudspeaker whose membrane is annular and whose enclosure has a central hole. Both toroidal loudspeaker and circular array radiate mainly in their normal axis, i.e., perpendicular to the plane comprising the membrane or the loudspeakers. Circular sound emitters are arranged like an end-fire array so that all the circular sound emitters centers are on the same axis. Each circular sound emitter is driven by its own signal, which results from a filtered version of the input signal, allowing the sound to be focused in the radiation direction.

André Roland S.A.2015

Conception acoustique de systèmes microtechniques

Jean-Daniel Lüthi

EPFL2011