Modèles Physiques et experimentation

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1 Modèles Physiques et experimentation
Anches doubles Modèles Physiques et experimentation Me: André Almeida working at IRCAM Work in cooperation with my supervisors (bla bla) and Christophe Vergez Work on the framework of my thesis project about Physical Modeling of double reeds André Almeida Christophe Vergez René Caussé Xavier Rodet Equipes Acoustique Instrumentale et Analyse Synthèse LMA – Laboratoire de Mécanique et Acoustique UPR 7051 Marseille

2 Modélisation physique
Résonateur Propagation Acoustique Comportement passif linéaire: Impédance While reed instruments are correctly described by simple models, double reeds’ specific timbre requires the introduction of further details My work is to try to find out what has to be added to describe the specificity of double reeds Hopefully it will allow to develop a physical model for most double reed instruments In the framework of my project, experiments play a fundamental work: Finding out, by observation of the proper variables what phenomena are most important in the behavior of double reeds When a reliable model is established, estimating the correct parameters to introduce in the model

3 Modélisation physique
Différence de pression débit Anche ouverte Anche plaquée Excitateur Comportement non-linéaire: Courbe caractéristique While reed instruments are correctly described by simple models, double reeds’ specific timbre requires the introduction of further details My work is to try to find out what has to be added to describe the specificity of double reeds Hopefully it will allow to develop a physical model for most double reed instruments In the framework of my project, experiments play a fundamental work: Finding out, by observation of the proper variables what phenomena are most important in the behavior of double reeds When a reliable model is established, estimating the correct parameters to introduce in the model

4 Modèles d’instrument à anche
Propagation linéaire Résonateur: pr pb pb pr Système Masse Ressort Anche: The physical model is derived from a generic reed instrument model: The reed is assimilated to a harmonic oscillator driven by the pressure difference between the mouth and inside the reed Bernoulli: . Pas de pertes . Pas de récupération de pression Ecoulement:  Quel est la différence entre une anche double et une anche simple?

5 Caractéristique non-linéaire
Vérifier que une anche double a un comportement différent d’une anche simple: Comparer les courbes caractéristiques Débit (Q) Pression (pb - p) Anche simple Débit (Q) Pression (pb - p) Anche double Experiments carried out at IRCAM allow us to access the 3 main variables governing (?) the behavior of the reed: pressure, flow and reed opening. We have developed an artificial mouth which substitutes the mouth of the instrumentist and allows to maintain a constant pressure driving the instrument. Physical variables are measured by: (probes, camera) Caractérisitques calculées sous certaines hypothèses simplificatrices

6 Caractérisation de l’écoulement
Caractérisation de l’écoulement d’air dans l’anche pj pr The reed film allows us to draw some observations: The two reeds move symmetrically, which confirms the hypothesis of modeling the double-reed as a single oscillator The reed completely shuts and remains closed for a small fraction of the period Smaller oscillation while the reed is open: reed resonance? Turbulence? Pertes de charge?

7 Suite The procedure of measuring reed opening through image analysis is simple, low-cost and advantageous in terms of a general study of the reed dynamics (It can be applied to other reed instruments). The current model seems to be coherent with our measurements, but its details still need to be fine-tuned. This will be done with further measurements of localized flow (at IRCAM) and complete fluid velocity field in cooperation with a Fluid Mechanics laboratory. Sur le poster…