The Physicist's Guide to the Orchestra

An experimental study of strings, woodwinds (organ pipe, flute, clarinet, saxophone and recorder), and the voice was undertaken to illustrate the basic principles of sound production in music instruments. The setup used is simple and consists of common laboratory equipment. Although the canonical examples (standing wave on a string, in an open and closed pipe) are easily reproduced, they fail to explain the majority of the measurements. The reasons for these deviations are outlined and discussed.Comment: 11 pages, 10 figures (jpg files). Submitted to European Journal of Physic

LE PIANO : MODÉLISATION PHYSIQUES ET DÉVELOPPEMENTS TECHNOLOGIQUES

Les principaux éléments du piano (mécanisme, marteau, cordes, étouffoir, chevalet et table d'harmonie) sont analysés dans leur fonctionnement mécanique et acoustique. Plusieurs procédés de synthèse (à vocation commerciale ou de création musicale) sont décrits ainsi que des voies possibles d'évolution de la facture de cet instrument.The main components of the piano (key mechanism, hammer, strings, damper, bridge and soundboard) are analysed in a mechanical and acoustical perspective. Some numerical-synthesis processes (designed for general public use or musical creation) are described and link is made between musical-acoustics research and future possible changes in the instrument-making

RÉSONATEURS CONIQUES : DESCRIPTION TEMPORELLE

An elementary time-domain analysis of the travelling of a pressure impulse along a clarinet leads to a natural understanding of the l/4 resonance. A plain transfert to a conical bore would lead to the same but erroneous conclusion. In a conical bore the velocity turns out to be responsible for the opening of the reed after only one around trip of the impulse. The near field velocity is dominated by a term which is ruled by the local pressure. Therefore an inversion of the pressure at the open-end is sufficient to ensure an inversion of the velocity when it comes back to the apex. This understanding provides with an alternate insight on the transition between cylindrical and conical bores

Identification of honeycomb sandwich properties by high-resolution modal analysis

A method is proposed to identify the mechanical properties of the skin and core materials of honeycomb sandwich. All the elastic coefficients and loss-factors that matter in the dynamics of a panel in the thick-plate approximation are identified. To this end, experimental natural modes (i.e. eigenmodes of the damped system) are compared to the numerical modes of a large sandwich panel (lx,y/h ≃ 80). The chosen generic model for the visco-elastic behaviour of the materials is E (1 + jη). The numerical modes are computed by means of a Rayleigh-Ritz procedure and their dampings are predicted according to the visco-elastic model. The frequencies and dampings of the natural modes of the panel are estimated experimentally by means of a high-resolution modal analysis technique. An optimisation procedure yields the desired coefficients. A sensitivity analysis assess the reliability of the method

Application expérimentale du bilan de puissance réactive à la mesure de l'anche de saxophone

The reactive power balance approach is capable of linking the dynamics of a reed represented by a spring and that of the resonator which is played. A simple-reed instrument do not play exactly at the frequencies of the impedance peaks. Therefore, each mode of the pipe absorbs (or provides) reactive power. Their sum is equal to that provided by the spring which stands for the reed in our model. We have experimentally determined the input impedance of a saxophone and its internal spectrum for various notes and playing conditions. The model yields a value for the stiffness of the reed when played by a machine or a musician. The measured values are consistent with those given by the literature on isolated reeds.La notion de bilan de puissance réactive permet de lier le fonctionnement d'une anche modélisée par un ressort à celui du résonateur qu'elle excite. Un instrument à anche simple ne joue pas exactement sur les fréquences des pics d'impédance. Chaque partiel du tuyau absorbe donc (ou fournit) une puissance réactive. Leur somme algébrique est égale à celle fournie par le ressort qui représente l'anche. Sur le plan expérimental, nous avons mesuré le spectre de pression interne d'un saxophone et son impédance d'entrée pour différentes notes et nuances. La modélisation précédente permet d'obtenir une détermination de la raideur de l'anche en situation de jeu. Les valeurs mesurées sont voisines de celles relevées dans la littérature sur des anches isolées

Une méthode de calibration simultanée des accéléromètres et des pots vibrants dans le plan transversal

The cross-axis sensitivity of accelerometers that is of the order of a few hundredths of the main axis sensitivity, is a common concern in vibration measurements. Usually the manufacturers do not provide a complete information upon the transverse sensitivity of transducers. The transverse motion of mechanical shakers is subject to the same problem and lack of information. The method that we present here is aimed at calibrating at the same time both defaults relatively to the axial components. By mounting an accelerometer on a shaker so that the main motion is perpendicular to the main sensitivity, its response adds up two products of the same order of magnitude : the main motion x the cross-axis sensitivity and the main sensitivity x the transverse motion. These two quantities are separated when the accelerometer rotates around the main-motion axis. All relative components of transverse motion and cross-axis sensitivity are derived from a combination of orientations of the accelerometer relatively to the main-motion axis. Measurements made with a variety of accelerometers exhibit a good consistency of the results concerning the transverse motion of a given shaker. Conversely, a good reproducibility of results pertaining to the cross-axis sensitivity of accelerometers has been achieved. The range in which that method is easily used with good results is limited in the low-frequency region by the motion of the shaker base and attachment

Les fluides magnéto-rhéologiques en tant que frein haptique : application au rendu de toucher de piano

Nous présentons une nouvelle interface sensorielle pour claviers numériques. Cette interface contient un actionneur semi-actif à base de fluides magnéto-rhéologiques capable de reproduire le comportement dynamique de la touche traditionnelle du piano à queue. L'actionneur est composé d'une plaque mince qui cisaille le fluide MR dans l'entrefer. Un noyau magnétique et des bobines permettent d'appliquer un champ magnétique variable sur le fluide et ainsi contrôler la viscosité apparente du fluide. Cette variation de viscosité se traduit par une variation de la force de cisaillement résistante. Cette force peut ainsi être contrôlée en temps réel