Sound activated Nikon Camera trigger?

We are doing research work generating airborne magnetoplasmoids, and one
problem has arisen relating to the use of 3 frame/second Nikon Digital
SLR camera. How do I trigger the camera to start a series of pictures
that begin immediately after the discharge that forms the
magnetoplasmoid? My initial idea was to use a feature of the remote
control (wire) that would initiate the start upon the sound noise
generated by the formation. However, Nikon USA informed me that the
output "sound activated box" the remote plugs into for this feature is
no longer manufactured or available. Assuming I plug the remote into a
homemade circuit, are there any thoughts on what kind of circuit I
should use that would trigger this feature from the sharp sound. I am
looking for a Radio Shack level of components.

I played with the three pin termination (actually banana plugs) and two
of them seem to be for a set of plus minus battery terminals, and the
other one triggered the camera with two quick touches to the minus
terminal.

The Nikon Capture 3 program has a glitch so I can't use the firewire to
start the event, at least until the Nikon Capture 4 version is shipped
to me in two or three months.

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