Active Damping Of A Vibrating String

Title	Active Damping Of A Vibrating String
Publication Type	Conference Paper
Year of Publication	2006
Authors	Berdahl, Edgar [1], Smith III Julius [2], and Freed Adrian [3]
Conference Name	6th International Symposium on Active Noise and Vibration Control
Date Published	2006/09/18
Conference Location	Adelaide, Australia
Abstract	This paper presents an investigation of active damping of the vertical and horizontal transverse modes of a rigidly-terminated vibrating string. A state-space model that emulates the behavior of the string is introduced, and we explain the theory behind band pass filter control and proportional-integral-derivative (PID) control as applied to a vibrating string. After describing the characteristics of various actuators and sensors, we motivate the choice of collocated electromagnetic actuators and a multi- axis piezoelectric bridge sensor. Integral control is shown experimentally to be capable of damping the string independently of the fundamental frequency. We consider the difference between damping the energy in only one transverse axis, versus simultaneously damping the energy in both the vertical and horizontal transverse axes. We discuss the advantages and drawbacks of various string actuators and sensors and described an experimental setup. We present waveforms of actively damped string vibrations and demonstrate that the sensors and actuators must be carefully aligned in order to obtain completely independent control of the vertical and horizontal transverse axes. Future work will involve implementing various sound effects for the electric guitar directly on a guitar string. For example, the tremolo effect consists of periodically varying the amplitude of an input signal, and so the active damping parameter could be varied periodically to achieve this effect. The waveforms corresponding to the model, the magenta poles displayed in the root loci, and the experiments are available from: http://ccrma.stanford.edu/~eberdahl/Projects/ActiveDamping/index.html [4]
URL	http://cnmat.berkeley.edu/publication/active_damping_vibrating_string [5]