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Sounds Of The Fourth: The Science Behind The Snap, Crackle, Boom


The Fourth of July is of course all about fireworks, the bursts of color in the sky, and also the sounds.


SHAPIRO: Of course here, we are little bit obsessed with sounds, and so we wondered why certain fireworks go boom and others crackle or whistle. Dr. John Conkling is a former executive director and technical director of the American Pyrotechnics Association.

Thanks for spending part of your Fourth of July with us.

JOHN CONKLING: My pleasure.

SHAPIRO: Do you actually design how a firework sounds, or is it a byproduct of the thing that's going to flash in the air?

CONKLING: They're rarely intentional except for several of the effects you mentioned. It's usually just a secondary phenomenon.

SHAPIRO: So what makes one thing pop when another thing whistles?

CONKLING: Well, it's the chemistry. It's the chemical mixture that's in the firework. And as that mixture burns, it can do different things with respect to sound production. The most typical sound you hear is the boom or the bang when a firework device explodes. That's typically a charge of good, old gunpowder or black powder that produces that effect. There are more modern bursting charges with metal powders in them that are sharper and louder and flash with a light effect as well so they will rock the ground when they function.

SHAPIRO: Are there ever silent fireworks? Are there things that make an incredible light display without making a sound?

CONKLING: The sound is largely a function of how tightly you wrap the firework device that's thrown up in the air. So if you have it very loosely wrapped, a minor pressure inside that firework will open up the package and light the contents. And there's a lot of interest in these quieter fireworks just because people don't like to bother the neighbors. They're trying to entertain the people in the immediate vicinity - particularly for theme parks and state fairs that have nightly fireworks shows over a period of time, and every night, those booms can start to, you know, to perhaps bother the residents around the area and so they ask, can you quiet them down? And the industry can do that.

SHAPIRO: What's the latest development in fireworks sounds?

CONKLING: There really hasn't been much for a few decades. We have the boom, the bang. We have the pyrotechnic whistle effect where you press a chemical mixture into a small tube, and as that burns, it pulses and it produces gas products, much as you create a whistle with a mechanical whistle. And then the newest effect is really the crackling effect where you have a chemical mixture that burns layer to layer to layer and crackles - gives a repeating bang, bang, bang, snap, snap snap. That's probably the latest thing in sound.

SHAPIRO: Do you have a favorite fireworks sound?

CONKLING: I love a loud boom.

SHAPIRO: (Laughter) Dr. John Conkling, former executive director and technical director of the American Pyrotechnics Association, thanks for your time and happy Fourth.

CONKLING: My pleasure. Nice talking with you. Transcript provided by NPR, Copyright NPR.

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