Charles Besnainou

Numerical simulation of a piano soundboard under downbearing

A finite element model of a piano soundboard is used to study the effect of the strings tension (downbearing) on its vibration, considering the ribs, the bridges and the crown. The downbearing is modeled with the prestress theory. Prestress calculation with linear and nonlinear models including geometric rigidity are compared in terms of the modal frequencies. The effects of the downbearing in modal frequencies and mobility are investigated and the importance of the crown on these results is evaluated. A simple phenomenological law is exhibited, which characterizes the evolution of eigenfrequencies with downbearing, including the initial crown.

Bow musical instrument made of composite material

A bow musical instrument in which at least the front (1) is constituted by a thin wall of composite material comprising at least two superposed sheets (A, B, C, D, . . . ) of crossed and directed long fibers, the wall being covered on at least one of its faces with a lining material (Y, Z) of considerably lower density than the fibers, wherein the deposition of the sheets of fibers is such that the ratio of the longitudinal modulus of elasticity divided by the transverse modulus of elasticity of the wall is higher in a wall zone close to the longitudinal axis of symmetry of the instrument than it is for a zone close to the sides of the instrument.

Prestressed Soundboards: Analytical Approach Using Simple Systems Including Geometric Nonlinearity

String instruments makers introduce prestresses on soundboards by adjusting the contact between the strings and the soundboard (downbearing). The effects of these prestresses on the vibration of the soundboard are investigated analytically, using a simple system of rods (one degree of freedom) and a buckled beam under the first two modes. For these two systems, we present successively the evolution of the eigenfrequencies and the nonlinear dynamical properties (phase diagrams, backbone curves). The two main results are 1) the second order evolution of the eigenfrequencies with prestresses are in agreement with a previous numerical simulation on a soundboard with the hypothesis of static large displacements and 2) the nonlinear dynamical properties of the system are modified by prestresses, and a prestressed soundboard working with large displacements seems to be technically possible.

Physical parameters of the violin bridge changed by active control

The physical parameters of a violin bridge have a significant influence on the tonal colouration of its sound. The resonance peaks of the bridge shape the response of the violin body. Reinicke and Cremer developed a simple bridge model that shows a typical broad frequency peak around 2.5kHz, because it incorporates the coupling to the violin body and the soundpost. By using the same model, Jim Woodhouse revealed the effect of some parameters of the bridge (mass, stiffness and foot spacing) on the instrument frequency response. Here the parameters of the violin resonance peaks are changed in real time, by applying an active control method. Such a technique, very useful in noise reduction, enabled to change separately the position and the shape of each peak of the bridge input admittance. On the bridge, 2 actuators and an accelerometer are placed at strategic positions in order to change the peak frequency and the damping factor values. The system behaviour is controlled by a Digital Signal Processor. Some sound results achieved with a real violin back up the theoretical equations.

Prestress effects on the eigenfrequencies of the soundboards: experimental results on a simplified string instrument.

This paper presents an experimental study of the effects of prestresses on the vibration behavior of string instruments. These prestresses are created by gluing ribs (crowning) and tensioning string (downbearing). The effects of these prestresses were previously studied numerically for a piano soundboard by Mamou-Mani et al. [J. Acoust. Soc. Am. 123, 2401-2406 (2008)] and analytically for simplified models by Mamou-Mani et al. [Acta Acust. Unit. Acust. 95, 915-926 (2009)]. In the present study, a specified test bench is designed, including a simplified soundboard (a rectangular plate), a bridge, and a single string. The plate is subjected to in-plane and transverse loads. Vibrational eigenmodes are identified using nearfield acoustical holography (NAH) measurement. The evolution of eigenfrequencies with these specific prestresses is studied. The results show the effectiveness of NAH for this purpose and a very good qualitative concordance with previous numerical and analytical calculus.

Composite materials for musical instruments: The maturity

Nowadays, musical instruments made of composite materials allow comparison with good instruments made by craftsmen. These instruments result from 20 years of accumulated experiments carried out in laboratories. The first substitute of wood was a composite of wood: plywood. Over 70 years with this new material, honorable results were obtained for an industrial line of products: piano, harp, guitar, double bass. However, composite materials made of fibers and resin are designed to imitate the structure of wood. So a specific knowledge is needed. The first attempts were on bows because it seemed easy; good results were obtained with fiberglass. The next step was to replace the neck of an electric guitar. However, it was a long time before acoustic elements such as a soundboard were designed. One needs first of all to develop a methodology to measure the mechanical parameters of wood: density, Young’s modulus, and damping; and to cross over the mechanical results with the subjective choices of expert craftsme...

Modifying the Resonances of a Xylophone Bar Using Active Control

A simple active control method is described which extends the possibilities of a xylophone bar. It allows the performer to modify the vibration of its structure, unlike post-processing effects involving loudspeakers. These variations change the characteristics of the partials radiated by the bar. The xylophone bar, made of composite material, is equipped with two actuators and one sensor in PVDF (polyvinylidene fluoride), the mass and stiffness of which do not modify the mechanical characteristics. A controller in a feedback loop is executed on a midrange digital signal processor. It is composed of a sum of second order band-pass filters. The selection of the controller coefficients relies on the measured transfer function between the input of the controller and the output of the sensor. First the active control method is designed to modify the resonance peaks of a simple model of a xylophone bar, whose transfer function is a superposition of three eigenmodes. Then it is applied to the real system. It is illustrated by increasing and reducing the amplitudes and/or frequencies of the first resonances, and by modifying the tuning of the xylophone bar.

Acoustic quality of musical instruments and categorization

The qualitative evaluation of high vintage musical instruments gives rise to several theoretical as well as technical questions. Depending on the experts, either instrument makers trained in various technologies or variously skilled and styled interpreters, the judgments rely on different criteria, regarding the object itself, its manipulations, as well as acoustic or aesthetic properties of the sounds it produces. Various experiments were run with classical guitars (Montchalin, 1993), harpsichords (Guyot, Castellengo, and Dumoulin, 1997), and violin bows (Saint‐Loubry and Besnainou, 1997). The judgments were processed in free categorization tasks of musical (listened or performed) sequences, followed by verbal comments on the partitions realized. The analysis of the psychological judgments of similarity and difference, and the linguistic processing of the verbal comments, led to the identification of the relevance of various perceptual modalities (not only acoustic but also kinaesthetic, haptic, and even...

Trekking around ancestors of smart instruments

In the present time, smart instruments are the ongoing revolution tying together acoustical instruments and computers. The concepts of electronic active control of structure are the heart of the process. The aim of this paper is to summarize more than one century of trials. Who remembers the “infinite sound” piano of Richard Eisenmann driven by electromagnetics and been touched, during the Industrial Art Exhibition in Munich in 1888, by Hermann von Helmholtz, and earlier the Pape’s enhanced piano with air blow? Some experiments revive the project as the E-bow dedicated for the steel-string guitar. Then, after a jump in the 1990’s as exercises for students on teaching feedback Proportional-Integral-Derivative analogical central heating regulator. On the cliff of the positive feedback applied for a xylophone bar, and so on just before numerical systems.

The jew's harp, experimental study and modeling

Under its archaic aspects jews harp is a musical instrument highly subtle. Indeed, a metal blade (or wooden) attached to a rigid frame put into vibration by the musician, and coupled to the buccal resonator allow nice tune. The skilt of the jews harp focuses on the conformations of this cavity whose function is to select the right components of the vibration to be amplify. In our study, we have modelled a playing technique which involves blowing during the blade vibrates. In the lake of breath, the spectre of sound produced by the blade is odd, i.e., it includes at first approximation odd components (n+1) multiple the fundamental. Whereas when the musician adds breath the spectrum turns into a spectrum containing all components of basic integer multiples (n). This work takes place in the context of studies of vibrating systems under prestress and loaded. In that case the load, and the prestress are generated by the musician breath by bending the blade On the other hand, experimental studies are compare ...