Like Magic! A Budget-Friendly Experiment to Control Standing Waves with a Speaker and String

Hello, I’m Ken Kuwako, your science trainer. Every day is an experiment.

Ever wondered what the shape of invisible “sound” looks like? You might picture pricey gear in a science lab, but the truth is, you can pull off surprisingly professional experiments using simple, everyday items. Today, we’re diving into the “standing wave” (teijou-ha) experiment, where a string seems to come alive and dance. Working with Mr. I from our school, we managed to build a high-performance, budget-friendly device using smart finds from a 100-yen shop. It’s a fantastic project for teachers and a perfect science fair idea for students at home.

The Science Recipe: Building Your Experiment with Everyday Items

You don’t need any fancy or specialized equipment to conduct a “physics experiment.” Here are the items you’ll need. The entire setup will cost you about the price of a single lunch!

What You’ll Need: A cheap speaker (you’ll be taking this apart). For instance, the 300-yen speaker we found at Daiso was quite powerful. Its 3W output allows us to shake the string more forcefully and dynamically. That’s part of the fun in science experiments—finding better components and upgrading your setup!

・Kite string (or similar) ・Weight (fishing weights or a bundle of five-yen coins work as a substitute) ・Cutting board rack (purchased at a 100-yen shop)

・USB charger/AC adapter (purchased at a 100-yen shop)

・A smartphone or iPad to be the sound source (Make sure to install a free “tone generator” app. Any app that can output specific frequencies will work.)

Now, let’s put these items together. Tie the kite string to the vibrating cone of the speaker. Run the other end over the cutting board rack, and use the weight to keep the string perfectly taut.

Time to flip the switch! When you start the vibration…

Check it out! You can clearly see the gorgeous wave patterns with the naked eye. We’ve managed to produce a standing wave that is far more visible than what older, professional lab equipment could show. It’s genuinely awe-inspiring!

Experiment Tips and the Mystery of ‘Resonance’

The mechanics of this experiment are simple, but they hold a profound concept. As you sweep the sound from a low pitch (low frequency) to a high pitch using the app, the moment it hits a specific frequency, the string will suddenly vibrate wildly and form a beautiful wave pattern. This is the phenomenon physicists call “resonance” (kyoshin), and the seemingly ‘frozen’ wave shape it creates is the “standing wave.”

Key to Success: It’s hard to find the “fundamental oscillation” (the state with one wave lobe) right away. Start by adjusting the frequency to look for the 3rd or 4th harmonics (the state with 3 or 4 wave lobes). These are relatively easy to find. The trick is to establish those, then predict and gradually lower the frequency to challenge yourself to find the 2nd harmonic, and finally, the fundamental oscillation. The fundamental oscillation might take a little time to stabilize into a clean shape after the string starts shaking, so be patient and wait it out.

A Pro Tip: The Vibration Modification Technique

I recently visited Narika and had the chance to check out their professional string standing wave apparatus (String Standing Wave Experiment Set). As you’d expect, it had more power than our DIY version and produced stunningly clear standing waves.

It’s interesting that turning the vibrator vertically seems to halve the frequency. We were able to clearly observe a phenomenon, perhaps similar to Melde’s Experiment. I decided to mimic this with my own Daiso-made device, wondering if pointing the vibrator upward and using a ruler would produce a clearer wave. It did! A beautiful standing wave was the result.

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