A vibrator assembly comprising: a shaft connected to a motor, the shaft including a track defining a path having a first component which travels circumferentially at least partially around the shaft and a second component which travels at least partially along a length of the shaft, wherein the shaft is configured to rotate under an action of a rotational force that is generated when the motor is activated; an unbalanced mass connected to the shaft, the unbalanced mass including a coupling for engaging and traveling along the track of the shaft, when the shaft is rotated, wherein when the motor is activated and the shaft is initially rotationally accelerated, the rotational speed of the unbalanced mass is less than the rotational speed of the shaft due to the rotational inertia of the unbalanced mass, such that when the unbalanced mass rotates at a speed less than the shaft, the unbalanced mass travels along the track toward an end of the path proximate a free-end of the shaft; wherein the track has an external helical screw form and the coupling of the unbalanced mass has an internal helical screw form, such that the internal helical screw form of the coupling mates with the external helical screw form of the track, the vibrator assembly being characterized in that it further comprises a tension device (212, 304) having a first end coupled to the free-end of the shaft and a second end coupled to the unbalanced mass, wherein when the motor is deactivated the unbalanced mass retracts under the action of a biasing force from the tension device (212, 304) from the end of the path to a rest position proximate the motor. a shaft connected to a motor, the shaft including a track defining a path having a first component which travels circumferentially at least partially around the shaft and a second component which travels at least partially along a length of the shaft, wherein the shaft is configured to rotate under an action of a rotational force that is generated when the motor is activated; an unbalanced mass connected to the shaft, the unbalanced mass including a coupling for engaging and traveling along the track of the shaft, when the shaft is rotated, wherein when the motor is activated and the shaft is initially rotationally accelerated, the rotational speed of the unbalanced mass is less than the rotational speed of the shaft due to the rotational inertia of the unbalanced mass, such that when the unbalanced mass rotates at a speed less than the shaft, the unbalanced mass travels along the track toward an end of the path proximate a free-end of the shaft; wherein the track has an external helical screw form and the coupling of the unbalanced mass has an internal helical screw form, such that the internal helical screw form of the coupling mates with the external helical screw form of the track, the vibrator assembly being characterized in that it further comprises a tension device (212, 304) having a first end coupled to the free-end of the shaft and a second end coupled to the unbalanced mass, wherein when the motor is deactivated the unbalanced mass retracts under the action of a biasing force from the tension device (212, 304) from the end of the path to a rest position proximate the motor.