Benjamin Elie

Macro parameters describing the mechanical behavior of classical guitars

Since the 1960s and 1970s, researchers have proposed simplified models using only a few parameters to describe the vibro-acoustical behavior of string instruments in the low-frequency range. This paper presents a method for deriving and estimating a few important parameters or features describing the mechanical behavior of classical guitars over a broader frequency range. These features are selected under the constraint that the measurements may readily be made in the workshop of an instrument maker. The computations of these features use estimates of the modal parameters over a large frequency range, made with the high-resolution subspace ESPRIT algorithm (Estimation of Signal Parameters via Rotational Invariant Techniques) and the signal enumeration technique ESTER (ESTimation of ERror). The methods are applied to experiments on real metal and wood plates and numerical simulations of them. The results on guitars show a nearly constant mode density in the mid- and high-frequency ranges, as it is found for a flat panel. Four features are chosen as characteristic parameters of this equivalent plate: Mass, rigidity, characteristic admittance, and the mobility deviation. Application to a set of 12 guitars indicates that these features are good candidates to discriminate different classes of classical guitars.

Acoustic signature of violins based on bridge transfer mobility measurements

This paper is an attempt to solve two problems related to musical acoustics. The first one consists in defining a signature of an instrument, namely, summarizing its vibroacoustical behavior. The second one deals with the existing relationship between the musical sound and the vibroacoustic properties of the instrument body. The violin is the application of this paper. A proposed solution for the first problem consists in an estimation of the bridge transfer mobility and the mean-value of the lateral bridge transfer mobility. The second problem is studied via the comparison between the amplitudes of harmonics, extracted from a glissando audio signal, and the lateral bridge transfer mobility: Both curves exhibit similar features. This is the main result of the paper. This is evidenced by studying the effect of a violin mute on both the lateral bridge transfer mobility and the produced sound. Finally, this is evidenced by successfully identifying which violin is played in an audio recording, using the computation of the Pearson distance between the distribution of the amplitude of harmonics and a database of measured mobilities.

Simulating alveolar trills using a two-mass model of the tongue tip

This paper investigates the possibility of reproducing the self-sustained oscillation of the tongue tip in alveolar trills. The interest is to study the articulatory and phonatory configurations that are required to produce alveolar trills. Using a realistic geometry of the vocal tract, derived from cineMRI data of a real speaker, the paper studies the mechanical behavior of a lumped two-mass model of the tongue tip. Then, the paper proposes a solution to simulate the incomplete occlusion of the vocal tract during linguopalatal contacts by adding a lateral acoustic waveguide. Finally, the simulation framework is used to study the impact of a set of parameters on the characteristic features of the produced alveolar trills. It shows that the production of trills is favored when the distance between the equilibrium position of the tongue tip and the hard palate in the alveolar zone is less than 1 mm, but without linguopalatal contact, and when the glottis is fully adducted.

Acoustic impact of the gradual glottal abduction degree on the production of fricatives: A numerical study

The paper presents a numerical study about the acoustic impact of the gradual glottal opening on the production of fricatives. Sustained fricatives are simulated by using classic lumped circuit element methods to compute the propagation of the acoustic wave along the vocal tract. A recent glottis model is connected to the wave solver to simulate a partial abduction of the vocal folds during their self-oscillating cycles. Area functions of fricatives at the three places of articulation of French have been extracted from static MRI acquisitions. Simulations highlight the existence of three distinct regimes, named A, B, and C, depending on the degree of abduction of the glottis. They are characterized by the frication noise level: A exhibits a low frication noise level, B, which is a transitional unstable regime, is a mixed noise/voice signal, and C contains only frication noise. They have significant impacts on the first spectral moments. Simulations show that their boundaries depend on articulatory and glottal configurations. The transition regime B is shown to be unstable: it requires very specific configurations in comparison with other regimes, and acoustic features are very sensitive to small perturbations of the glottal configuration abduction in this regime.

Reflexion of flexural waves at the end of a tapered beam of quadratic profile covered with a thin viscoelastic layer

Flexural waves propagating in a beam can be efficiently absorbed if one extremity is tapered with a power law profile and covered by a very thin viscoelastic layer (V. Krylov, JSV 274 (2004), 605-619). Such a terminaison induces an effect known as ?the acoustic black hole effect? (ABH), which is resulting from properties of propagation of flexural wave in beams having non homogeneous thicknesses: if the thickness decreases locally, flexural waves slow down and the amplitude of the displacement field increases, leading to efficient energy dissipation if an absorbing layer is placed where the thickness is minimum (V. Georgiev et al., JSV 330 (2011), 2497-2508). Absorption of the ABH terminaison is estimated thanks to the direct measurement of the reflexion coefficient, using a wave decomposition technique. Experimental modal Analysis of a ABH beam can be performed using a high resolution technique which permits to estimate the modal density. Analysis of these experimental results is performed thanks to a mo...

Vibroacoustics of a gothic harp.

The gothic style of harp was popular across most of Europe from the late medieval period to the Renaissance. To study the vibroacoustic behavior of gothic harps, one was constructed from plans created by the Boston Museum of Fine Arts from a late German model in their collection. The vibrational behaviors of the soundboard and soundbox were measured at various stages of construction of the instrument. Once complete, the instrument was subjected to modal analysis and radiativity measurements using Weinreich’s method. The sound radiation of this harp is dominated by two breathing modes at 188 and 273 Hz and higher modes around 350 Hz, which together function like the A0/T1 resonance pairs seen in the soundboxes of many other instruments including modern concert harps. As the frequency increases, radiation is emitted from higher up the soundboard and from higher soundholes, as has been observed in other harps. Unlike modern instruments, the gothic harp’s thin back plays a large role in sound production.