Paper Crackles

Crackling noise demonstration

Find a piece of paper. Holding it next to your ear, crumple it slowly into a ball. What do you hear? Crackling noise!

Where does the noise come from? Take your crumpled paper, flatten it out part-way, and then wiggle it back and forth. Can you make one spot jump in and out? When the spot jumps in and out, it makes noise.

Paul Houle studied this noise for a summer project in his second year in graduate school at Cornell. We started by just crumpling paper by hand in front of our computer's microphone.

Because he wanted to be able to crumple exactly the same way each time, and because he wanted other people with smaller fingers to be able to crumple the paper the same way he did, Paul devised an ingenious instrument for crumpling, out of two bean cans and some tape.

Here is some of Paul's data. Each spike (big vertical line) is a crackle. Some are much, much larger than others! Paul found ways to teach the computer to separate the crackling noise into separate crackles, and taught it to measure the size of each crackle.

What did we learn?