What actually makes a shell ‘whistle’ – is it a different powder or just the tube shape?

[Danny Roth]

#6218

So I finally got my hands on a case of whistling shells last show and I can’t stop thinking about it. That rising scream before the burst is half the fun honestly. But what’s the actual trick? Is it a special comp in the lift or is the casing shaped weird so the gas does that? Tried googling and just got marketing junk. Someone who knows pyro, break it down for me.

[Steve Kline]

#6221

tbh it’s the comp, not the tube. Traditional whistle mix is mostly potassium benzoate (or sodium benzoate) with a little perchlorate – when it burns it oscillates instead of burning steady, so it makes that shriek at a few thousand Hz. The tube mostly just tunes it, a longer tube drops the pitch a bit. It’s the same chemistry as those little whistle rockets, just packed into a small tube built into the shell so it burns before the burst. Either way it never gets old at a show.

[Ron Butler]

#6222

The scream into the boom is the best part and I’ll die on that hill. Knew a guy who’d pick out all the whistling shells from a mixed case and save em for the finale so the whole sky sounded like it was tearing open. Worth it.

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