masses m 1 and m 2 as shown in fig4 and corresponding to the arrangement of fig2 the equations of motion for the two masses are in this case the forces transferred by the springs to platform 22 are equ3 the resulting force equ4 thus becomes zero if u03c9 1 u03c9 2 i e if the two spring mass systems have the same natural frequency i e c 1 c 2 m 1 m 2 in the arrangement of fig2 the voice coil motor ensures that the movements of the oscillation systems proceed invariably phase opposed to each other since the magnetic field between the energizing coil and the field coil of the voice coil motor exerts the same force on the two masses furthermore it is assumed that the environment of the whole system is at a total rest i e that no spurious forces from the outside act on the platform if such spurious forces cannot be discounted for example when platform 36 is horizontally adjusted it is recommended that the two oscillation systems be forcibly coupled to each other the forced coupling ensuring that even when external spurious forces become effective the mass systems move in opposite directions rather than in the same direction if the oscillation.