An improved bowed roll assembly and system that can be adjusted during operation to alter critical speeds to outside the range of the operational speed of the assembly, and methods of altering critical speeds of the roll assembly during its operation to inhibit harmonic vibration are provided. In one embodiment, the bowed roll assembly system includes a programmable logic controller (PLC) and accelerometer, and the critical speeds of the roll assembly are nulllearnednull by the PLC which triggers changes to the pressure of the pressure applying member of the assembly to alter the roll's stiffness and the critical speeds.