Abstract: An armature for an actuator for applying vibration to a body along an axis, the armature having at least two parallel wound helical windings on the axis, and a terminal arrangement connected to the ends of the windings for selective connection of the windings to two external A.C. drivelines, the terminal arrangement being switchable between a relatively low impedance mode, with at least two of the windings connected electrically in parallel, and a relatively high impedance mode, with two of the windings or two groups of parallel-connected windings connected in series.