Abstract: A vibratory system for a screening and/or feeder machine, the vibratory system including shaft lines, each shaft line having an unbalance module, the vibratory system also having a drive device configured to drive the shaft lines in rotation in synchronous manner and in the same direction. The vibratory system also includes an angle modifier device configured to modify the angular position of the unbalance module of one shaft line relative to the angular position of the unbalance module of the other shaft line or of one of the other shaft lines.