Motion of the cello bridge.

This paper presents an experimental investigation of the motion of the bridge of a cello, in the frequency range up to 2 kHz. Vibration measurements were carried out on three different cellos, and the results used to determine the position of the Instantaneous Centre of rotation of the bridge, treated as a rigid body. The assumption of rigid body rotation is shown to give a good approximation up to at least 1 kHz. The instantaneous centre moves from the sound-post side of the bridge at the lowest frequencies towards the bass-bar side at higher frequencies, remaining close to the surface of the top plate of the instrument. The trajectory as a function of frequency sheds light on the response of the cello in response to excitation by bowing the different strings. The correlation between the motion at the four string notches and directly measured transfer functions at these four notches is examined and verified for some important low-frequency body resonances.