Feel Sound Waves Collide! Experience the “Beating” Effect at Home Using Just 2 Smartphones
I’m Ken Kuwako, the Science Trainer. Every day is an experiment.
Experience “Beats” at Home! A Simple Sound Experiment Using Two Smartphones
Have you ever heard a sound that seems to wobble or pulse strangely? That mysterious effect is called a beat, and the good news is—you can easily experience it at home. In this article, we’ll show you how to observe beats using just two smartphones or tablets.
What Are “Beats”?
Beats occur when two sounds with slightly different frequencies are played at the same time. As the sound waves overlap, they alternately strengthen and cancel each other out, causing the volume to rise and fall repeatedly. This creates the familiar “wah-wah” or “woo-woo” effect.
For example, if you play a 440 Hz tone together with a 442 Hz tone, you’ll hear a beat twice every second. The number of beats per second exactly matches the difference between the two frequencies. This isn’t a coincidence—it’s caused by a physics principle known as wave superposition.
In fact, professional instrument tuners use beats all the time to fine-tune musical instruments!
Watch the Experiment in Action
First, check out this video. In addition to demonstrating how to observe beats, it also explains how tuning forks work and the role of resonance boxes.
The “talking tape” introduced in the video can also be found at toy stores.
https://phys-edu.net/wp/?p=46797
Compare the Sounds Yourself
Mr. M created a program that plays different sound patterns through speakers. It’s a great teaching tool for classrooms, too. Try listening carefully to Sound 1 and Sound 2 and compare them.
1. 440 Hz tones in phase from both left and right speakers
2. 440 Hz from the left speaker and 440 Hz from the right speaker (out of phase)
Compared with Sound 1, doesn’t Sound 2 feel slightly more muffled or cloudy? That happens because the out-of-phase waves partially cancel each other out.
Even though both sounds are exactly 440 Hz, simply changing the phase dramatically changes how we perceive the sound. Physics can be surprisingly audible!
Try Hearing Beats for Yourself
In the next audio sample, the left speaker plays 400 Hz while the right speaker plays 402 Hz. Since the difference is 2 Hz, you should hear two beats every second. You can even try this on an iPad or tablet.
3. 400 Hz from the left speaker and 402 Hz from the right speaker (beats)
Once you can hear the beats, try covering the left speaker with your hand. The pulsing sound suddenly disappears, doesn’t it?
That’s because beats only occur when two sound waves overlap. Remove one of the sounds, and the interference vanishes instantly. It’s a great way to physically experience wave behavior with your own ears.
Beats are one of the most beautiful examples of wave interactions in nature. With just a smartphone or tablet, you can easily explore this phenomenon at home. Try it with your family or friends and see who notices the effect first!
We also introduce other fun experiments using tuning forks, so be sure to check those out too.
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