Effects of internal resonances in the pitch glide of Chinese gongs

• Published in: The Journal of the Acoustical Society of America 2018-07, Vol.144 (1), p.431-442
• Main Authors: Jossic, Marguerite, Thomas, Olivier, Denis, Vivien, Chomette, Baptiste, Mamou-Mani, Adrien, Roze, David
• Format: Article
• Language: English
• Subjects: Acoustics; Mechanics; Physics; Solid mechanics; Vibrations
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.5038114

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.