Assessing tuning and damping of historical carillon bells and their changes through restoration

The 46 bells of the historical carillon in Perpignan have been restored: taking them down, sanding their oxide layer, and resuspending them. Sound and vibration recordings were made at each stage of the restoration process. The modal frequencies and decay rates have been estimated by means of the matrix pencil algorithm, a parametric signal processing method, with a variance of ≈ 0.1% for the frequencies and a few percents for the damping rates. Tuning is accurate in general, except for the highest notes. The quality factors of the vibration go through a broad minimum in the 2 kHz region. Measurements reveal minute but consistent frequency changes of the order of a few cents. On average, the bells ring 15% longer since the restoration. The measurements also show that the damping rates were more consistent along the range of the instrument after restoration.