A method of operating a vibratory testing apparatus, the method comprising: providing a table frame with at least one vibrator attached thereto, the at least one vibrator having - a sealed body with first and second ends and defining a cavity therein, the cavity having first and second ends (38, 40); - a first air passage in the sealed body near the first end of the body, the first air passage configured to allow gas to flow to and from the first end of the cavity; - a second air passage in the sealed body near the second end of the body, the second air passage configured to allow gas to flow to and from the second end of the cavity; and - a piston within the cavity and moveable between the first and second ends (38, 40); attaching the at least one vibrator to a four-way solenoid valve having an in port, a first and a second in/out port (30, 32) and an exhaust port, the four-way solenoid valve capable of being switched between a first and a second position, connecting the in port of the solenoid valve to a pneumatic air supply and connecting the first air passage of the vibrator to the first in/out port and the second air passage to the second in/out port; connecting the solenoid valve to a controller, the controller being capable of controlling the four-way solenoid valve to allow air from the pneumatic air supply to the vibrator in the first and second position in bursts, a burst in the first position moving the piston to impact with the body of the vibrator at the second end of the cavity and a subsequent burst in the second position moving the piston to impact with the body of the vibrator at the first end of the cavity, characterized by controlling the frequency of the impacts by switching the four-way solenoid valve via the controller, and controlling the amplitude of the impacts via the amount of pressure supplied to the four-way solenoid valve independent of the frequency of the impacts. providing a table frame with at least one vibrator attached thereto, the at least one vibrator having - a sealed body with first and second ends and defining a cavity therein, the cavity having first and second ends (38, 40); - a first air passage in the sealed body near the first end of the body, the first air passage configured to allow gas to flow to and from the first end of the cavity; - a second air passage in the sealed body near the second end of the body, the second air passage configured to allow gas to flow to and from the second end of the cavity; and - a piston within the cavity and moveable between the first and second ends (38, 40); - a sealed body with first and second ends and defining a cavity therein, the cavity having first and second ends (38, 40); - a first air passage in the sealed body near the first end of the body, the first air passage configured to allow gas to flow to and from the first end of the cavity; - a second air passage in the sealed body near the second end of the body, the second air passage configured to allow gas to flow to and from the second end of the cavity; and - a piston within the cavity and moveable between the first and second ends (38, 40); attaching the at least one vibrator to a four-way solenoid valve having an in port, a first and a second in/out port (30, 32) and an exhaust port, the four-way solenoid valve capable of being switched between a first and a second position, connecting the in port of the solenoid valve to a pneumatic air supply and connecting the first air passage of the vibrator to the first in/out port and the second air passage to the second in/out port; connecting the solenoid valve to a controller, the controller being capable of controlling the four-way solenoid valve to allow air from the pneumatic air supply to the vibrator in the first and second position in bursts, a burst in the first position moving the piston to impact with the body of the vibrator at the second end of the cavity and a subsequent burst in the second position moving the piston to impact with the body of the vibrator at the first end of the cavity, characterized by controlling the frequency of the impacts by switching the four-way solenoid valve via the controller, and controlling the amplitude of the impacts via the amount of pressure supplied to the four-way solenoid valve independent of the frequency of the impacts.