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Assembly and Operating Instructions for Kits


Operation of the Sound Trigger 4


Assembly instructions for other kits


Click on any photo to enlarge.

Sound Trigger 4

Figure 1

Sound Trigger 4 control box

Microphone cable

Figure 2

Microphone cable


RCA flash trigger cable, assembled

Nikon MC-30 shutter cable

Figure 3

Flash trigger cable

(RCA type)

Figure 4

Shutter cable for camera

(photo shows cable for a Nikon camera)




When used with the microphone cable shown in Figure 2, the Sound Trigger 4 provides a sensitive detector of sound-producing events for high-speed photography. The Sound Trigger 4 can trigger a flash unit, camera shutter, or Delay Timer.

Installing a Battery

Before using the trigger, you’ll need to install a 9-V battery. Remove the 4 corner screws holding the lid to the box. Lift off the lid carefully. Insert a fresh battery into the battery holder, making sure that the contacts snap securely to the battery. If desired, the battery holder can be removed to help with the installation. Velcro connects the holder to the box. If removing the battery holder, be careful not to stress the red and black wires to the lid. When the battery is installed, close the lid carefully to make sure not to pinch any wires between the lid and the case. Then screw the lid back on.


Follow these steps to set the sensitivity and check that the unit is working correctly.

  1. Flip the power switch to the ON position. The Power LED should light.
  2. Press the red Test button on the right. The Trigger LED should light to indicate that the unit has been triggered.
  3. Plug the microphone cable into the port labeled Mic In. Turn the sensitivity knob to the midway (5) position. Snap your fingers near the microphone. This should trigger the unit. You can test for sensitivity by backing away from the microphone while snapping your fingers or clapping. In order to increase sensitivity, turn the Sensitivity knob to a higher number. For loud sounds, use a lower sensitivity setting to avoid accidental triggering from environmental noises.

The Flash Output

In order to connect a flash unit to the Flash output of the Sound Trigger, you’ll need the appropriate cord. The end of the cord that plugs into the box must have an RCA-type plug, such as the one shown in Figure 3. The other end of the cord plugs into the flash unit. If the flash unit has a PC jack, then the cord would need to have the corresponding PC plug, again as shown in the photo. If the flash unit doesn’t have a PC jack, then a hot-shoe adapter with a PC jack can be used to make the connection.

With a flash unit connected to the Flash output and turned on, the flash will discharge in response to a triggering event. The delay between the triggering event and the discharge of the flash depends on the distance between the source of sound and the microphone. You can adjust the delay fairly precisely simply by adjusting the distance. Use the fact that sound travels approximately a foot (30 cm) in air each millisecond. (1 ms = 0.001 s) An adjustment of a little more than an inch (3 cm) changes the delay by about 0.1 ms (0.0001 s).

While using distance to adjust delay works very well, there are some situations where the delay needed may be so great that it would be inconvenient or impossible to move the microphone far enough from the sound-producing event. In such cases, you can connect the Flash output of the Sound Trigger to the Input of a Delay Timer in order to generate delay intervals electronically. In order to make the connection, you’ll need a cable with an RCA plug on one end and a 3.5mm mono plug on the other.

The Timeout Switch

The timeout is the time after discharge of the flash unit (or actuation of a camera shutter) during which the Sound Trigger circuitry will not accept another trigger signal. The purpose of this feature is to prevent a multiple-exposure from an output signal that follows too closely after a previous output signal. This can result from echoing of sound when working in a small room, especially one without many sound-absorbing materials. In such cases, use the Long position for the Timeout switch.

You can test how the Timeout works as follows: 1) Connect your flash unit to the Flash output, 2) set the Timeout switch to Long, 3) press the Test button twice in quick succession. The flash should discharge on the first press but not the second. Now flip the Timeout switch to the Short position and repeat the double press. The flash unit will likely discharge twice. If it doesn’t, this may be a result of your flash unit having to take time to recharge.  The lower the power setting for your flash unit, the less the recharge time will be. Note that on the Long Timeout setting, the Trigger LED will remain on throughout the timeout interval.

The Shutter Output

In order to trigger a camera shutter, connect the shutter cable to the Shutter port. This requires a 3.5mm stereo plug on one end and the appropriate connector for the camera’s shutter port on the other. See Figure 4.

3.5mm female - RCA male adapter
Note that the Shutter output can be used to discharge a flash unit rather than actuate a camera shutter. This provides a way to discharge two flash units simultaneously. When connecting to a flash unit, an adapter is needed to convert the RCA plug of the flash cable to a 3.5mm plug needed by the Shutter port. The adapter shown to the right is available here.

Note about optoisolation: The Shutter port is optically-connected—as opposed to electrically-connected—to the trigger circuitry. Thus, the Sound Trigger cannot damage your camera. This, however, is not necessarily true if you use the Shutter port to discharge a flash unit. The voltage at the Shutter port can be no higher than 80 V in order to prevent the optoisolator from burning out; however, some legacy flash units have internal synch circuits with voltages up to 400 V. Such flash units may not be used. While modern units don’t have this problem, we don’t recommend using the Shutter port to trigger a flash unit if you’re not sure what the synch voltage of your flash unit is. If you want to check the synch voltage, there are videos on YouTube describing the process.

Note about wireless triggering: If you use a wireless transceiver, then you can plug the transceiver into the flash output of the Sound Trigger and thereby trigger the flash wirelessly. If you use the latter method, keep in mind that the transceiver circuitry may introduce a delay of a few milliseconds before the flash discharges. This may or may not be important, depending on the event to be photographed.

The Pulse Output

The Pulse Out port provides a low current pulse of about 9 V. This can be used to trigger flash units or other devices that require a low voltage pulse for triggering. Connection is made to the Pulse Out jack with an RCA plug. Note that the Pulse Out port will only power light loads and should never be used to power an inductive load. This may damage the Sound Trigger circuitry.

The Aux In port

The Aux In port can be used with any external trigger that has a simple switch output. An example is a contact trigger, which is actuated by bringing two metal wires or plates together. The port requires a 3.5mm mono plug. When an external trigger is plugged into the Aux In port, the microphone and corresponding sensitivity controls are not functional; however, all the other trigger functions will work, including the timeout switch.

Remote triggering may be achieved through the Aux In port by connecting a radio transceiver.



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