Hi Slingshot, yes it was a 5 second exposure, let me explain...
Basically, you set the camera to a 5 second exposure in a very dark room, I also used a black background, so once the exposure is taken, there is nothing but black. Then I rigged my SB-800 flash unit to a sound trigger which I borrowed off a very good friend of mine! So the flash was now controlling the exposure instead of the camera.
To set up I started by clapping once, very quickly, to get the focus right and the exposure as close as I could, then went from there.
Then I inflated the balloon and used a long screw driver with a pin taped to the end to pop it, which was fun trying not to stab myself in the face with a pin in the dark!
The problem with the exposure was there were so many things to take into account which vary the final result. Anyone out there who thinks this is easy with a sound trigger, think again!
Things to consider:
1) Camera ISO and F-stop, to account for the long exposure and keep it dark so there is no ghosting image of a balloon, plus I had to compensate this to account for the flash speed, so every adjustment I made I had to look at the camera as well.
2) The flash had to be incredibly fast, anything slight too long left a ghost like balloon and a piece of dissapointing rubber hanging over your hand, also blew out the image "no pun intended"
3) I had to keep using the same type of balloon as they popped at different speeds, also I had to ensure I inflated it exactly the same every time otherwise it popped at different speeds as well, so the larger you inflate the balloon the quicker it popped.
4) I adjusted the sound trigger, by moving the position of the microphone it adjusted the reaction of the flash to the bang, there is also a trigger delay on the device which I used. So I ended up with the mike up my sleave right next to the balloon.
Any one item you adjust, everything else had to adjust, it just went on and on. As I have a 19 month old daughter in bed, I decided to go into the garage in the dead of night to get the shot, so all my neighbours heard loud bangs and saw flashes coming from my garage, I am surprised the armed response police were not called! LOL
It was an excellent experience to do this. I think a water balloon would be easier as it pops slower, so you can get a better exposure.
Sorry for the long explenation, hope it helps.