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.