In order to control vibrations of two parts of a piece of machinery, a variable force may be generated to oppose the vibrations, with the variable force being generated under control of a controller on the basis of an iterative relationship, the iterative relationship being such as to generate the force of one iteration using a controller output signal in frequency domain vector form derived from the controller output signal of the immediately previous iteration in frequency domain vector form plus a frequency domain vector quantity derived from the resultant vibration of more than one previous iteration.Where these two parts are connected by multiple (f) mounting devices, the controller output signals a previous iterations are taken into account, and the frequency domain vector quantity derived from the controller output signals and more than f previous iterations.The information corresponding to the vibration frequency may be derived from a rotating shaft, where the two parts are the engine and chassis of a vehicle.It is also possible generate a force between the two parts which is a harmonic of the frequency of vibration being suppressed.