the vibrating assembly is a moving element driven either by hydraulics or more commonly, electromagnets. in the electromagnetic version, the heart of this assembly is a tuned spring-mass system powered by electrical coils acting on oppositely charged lamination stacks. the frequency of the electrical charges is matched to the mechanical frequency of the system. although the amplitude can be adjusted on the machine the frequency can only be changed by changing the mass of the vibrating assembly. the moving portion of the tooling is affixed to the vibrating assembly.