Physical modelling of a harp from Central Africa.

Central Africa harps are string instruments, often anthropomorphic, serving an essential cultural role. Compared to pedal harps, their body is small in size with a soundboard mainly made of animal skin and a neck made of a wood beam. In this paper, a physical model is developed as a tool for assessing the specificities of these musical instruments, from a vibro-acoustic perspective. The modeling strategy is based on the modal Udwadia-Kalaba formalism which is a multibody substructuring technique. Input modal parameters of the body and the strings are experimentally identified and the main steps of the estimation procedures are detailed. The reliability of the physical model is investigated via the comparison between simulated and experimental data for several plucking configurations. Different hypotheses are assessed such as the string/neck coupling which proves to strongly influence the dynamic response of the body when there is a coincidence between string and neck modal frequencies. The inclusion of geometrical nonlinearities proves to be of major importance, even for a weak plucking, as it allows qualitative representation of double frequency terms in the simulations. Overall, physical simulations of the soundboard motion are in good agreement with measurements indicating characteristic features of the instrument are captured.

Influence of the player on the dynamics of the electric guitar.

The sound of the electric guitar is strongly dependent on the string vibration. Where a mode of the structure coincides with a mode of the fretted string, coupling between the string and structure occurs at that "deadspot." The coupling significantly lowers decay time, leading to the name [Paté, Le Carrou, and Fabre (2014). J. Acoust. Soc. Am. 135(5), 3045-3055]. But how the guitarist affects the dynamic behavior of the structure by grasping the neck, holding the instrument with the strap, or laying the instrument on his/her thigh remains to be investigated. This is the aim of the paper. Two methods are proposed to identify the modal parameters of the electric guitar structure, either by a classical modal analysis in simulated playing configuration, or by an operational modal analysis in real playing configuration. For this latter method, modal parameters are identified from dynamic measurements performed when each string is plucked. Both methods are compared and allow one to quantify the modal frequency modification and the added modal damping, which depend on the player's body-part in contact with the structure and on the modal shape considered. Consequences of these modal parameters on the modeled sound show that the player can increase the decay time close to a deadspot.

Effects of internal resonances in the pitch glide of Chinese gongs.

The framework of nonlinear normal modes gives a remarkable insight into the dynamics of nonlinear vibratory systems exhibiting distributed nonlinearities. In the case of Chinese opera gongs, geometrical nonlinearities lead to a pitch glide of several vibration modes in playing situation. This study investigates the relationship between the nonlinear normal modes formalism and the ascendant pitch glide of the fundamental mode of a xiaoluo gong. In particular, the limits of a single nonlinear mode modeling for describing the pitch glide in playing situation are examined. For this purpose, the amplitude-frequency relationship (backbone curve) and the frequency-time dependency (pitch glide) of the fundamental nonlinear mode is measured with two excitation types, in free vibration regime: first, only the fundamental nonlinear mode is excited by an experimental appropriation method resorting to a phase-locked loop; second, all the nonlinear modes of the instrument are excited with a mallet impact (playing situation). The results show that a single nonlinear mode modeling fails at describing the pitch glide of the instrument when played because of the presence of 1:2 internal resonances implying the nonlinear fundamental mode and other nonlinear modes. Simulations of two nonlinear modes in 1:2 internal resonance confirm qualitatively the experimental results.

Modal active control of Chinese gongs.

Instruments that belong to the gong family exhibit nonlinear dynamics at large amplitudes of vibration. In the specific case of the xiaoluo gong, this nonlinear behavior results in a pitch glide of several modes of the instrument in addition to harmonic distortion and internal resonances. This study applies a linear modal active control to a xiaoluo gong in an attempt to change its sound properties. First, a modal damping control of the fundamental mode based on a linear identification and a state space controller is applied in the small amplitude regime (no pitch glide). Results indicate that modal control influences not only the controlled mode but also the frequency components involved in distortion or internal resonance phenomena. Second, a modal damping control is performed in the large amplitude regime (in the presence of pitch glide). Results show that modal control does not affect the pitch glide. However, the controller becomes effective at a time trigger which is related to the instantaneous frequency.

Active control and sound synthesis--two different ways to investigate the influence of the modal parameters of a guitar on its sound.

The vibrational behavior of musical instruments is usually studied using physical modeling and simulations. Recently, active control has proven its efficiency to experimentally modify the dynamical behavior of musical instruments. This approach could also be used as an experimental tool to systematically study fine physical phenomena. This paper proposes to use modal active control as an alternative to sound simulation to study the complex case of the coupling between classical guitar strings and soundboard. A comparison between modal active control and sound simulation investigates the advantages, the drawbacks, and the limits of these two approaches.