The Magic of “Sound Cancelling Sound”! Visualizing Noise Cancellation with an iPad

I’m Ken Kuwako, your Science Trainer. Every day is an experiment!

Imagine the hustle and bustle of the city or the deafening roar of a jet engine vanishing in an instant, leaving you in a world of pure silence where only your music remains. Are you using “Noise-Canceling” technology? While it’s now a standard feature in our smartphones and earbuds, there is actually an amazing application of wave physics hidden behind the scenes. Today, I want to share a unique way to let an entire classroom witness this invisible power to silence sound!

The Science of Creating Nothingness by Colliding Waves

At its core, “sound” is simply a vibration of air that travels as a wave. In a nutshell, noise-canceling technology works by using sound to cancel out sound.

A microphone picks up the surrounding ambient noise, and the system instantaneously creates an identical wave but in reverse (this is called an inverted phase). When these two waves collide, the peaks of one meet the valleys of the other, flattening the wave and causing the sound to disappear. In physics, we call this the Principle of Superposition. Here is what it looks like when demonstrated with a spring:

In my classes, I often have a student put on my favorite pair of headphones. The moment I flip the switch, the “hum” of the air conditioning vanishes. The student’s eyes go wide in surprise at the sudden silence. Since it blocks out distractions, it’s also the perfect tool for when you really need to focus on your studies!

Scaling the “Wow” Moment from One Person to the Whole Class

The only problem is that headphones are a solitary experience. While one student is amazed, the rest of the class is just watching, making it hard to share that “magic” moment. Buying headphones for everyone is also way too expensive! So, I wondered, “How can I visualize this magic for everyone at once?” That’s when I came up with an experiment using a tablet’s microphone. It was a huge hit, so here is the recipe!

The Science Recipe

What you need: Noise-canceling headphones, iPad

The Method: First, take a look at the dramatic change in this video.

When we use an app to observe the sound waves, the results are crystal clear. When the function is OFF, the wave jumps wildly as it picks up the surrounding noise.

But the moment we switch it ON, you can see the waveform shrink significantly.

Tips for Turning a Tablet into a Scientific Instrument

For this experiment, I used an app called “Soundbeam,” which visualizes sound as waves. Tablets like the iPad usually have their microphones located near the camera…

The trick is to cover that specific area with the ear cup of the headphones. By toggling the switch and projecting the changing waveform onto a screen, the entire class can share the moment sound is literally cancelled out. By the way, smartphones often have microphones in multiple locations, which can make this tricky, so I highly recommend using a tablet like an iPad for the best results.

The laws of physics are hidden inside the technology we use every day. With just one tablet, your classroom can transform into an exciting laboratory. Why not try observing the “waveform of silence” for yourself?

Reference: Other examples of wave reflection

Reflection at a free end

Reflection at a fixed end

Longitudinal and Transverse waves

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