An electrodynamic vibration test system, also referred to as a shaker apparatus, includes many components but the transmission of vibration to a unit under test is limited to three while testing is performed in the horizontal mode and only two key items in the vertical mode. In the horizontal test mode, the armature is mechanically joined to a driver bar which is also mechanically connected to a slip plate. In the vertical mode the moving parts include a head expander mechanically connected to an armature. With the use of composite materials for the moving elements, total weight is decreased by fifty percent or more resulting in a power usage decrease while simultaneously increasing force capability.