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Uploaded:2016-04-21
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Electronic music is older than you may think. Enter the theremin - a device that turns your body into part of a capacitor, and allows you to play music without even touching an instrument!

Special thanks to Jay Bruns of nojayart.com for lending us his theremin, and Mike Emmons for setting up our meeting.

Hosted by: Hank Green
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Sources:
http://web.physics.ucsb.edu/~lecturedemonstrations/Composer/Pages/60.17.html
http://electronics.howstuffworks.com/gadgets/audio-music/theremin.htm
http://www.animations.physics.unsw.edu.au/jw/LCresonance.html
http://www.facstaff.bucknell.edu/mastascu/elessonshtml/lc/capac1.htm
https://books.google.com/books?id=6DHlQJcMpBQC
http://web.physics.ucsb.edu/~lecturedemonstrations/Composer/Pages/44.51.html
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/beat.html#c3

(Intro)

Hank: Electronic music is not for everyone. Whether it’s dubstep, or techno, or electro-swing, or darkstep, or acid jazz, the unique sounds, beats, and rhythms are only possible thanks to some pretty slick, but simple, technology.

Even though they seem like a modern invention, electronic instruments have been around for a lot longer than you might think. Léon Theremin, a Russian inventor and professor of acoustics, created one of the first ever electronic instruments in the 1920s called the etherphone. Or at least, that’s what he called it. Now we call it the theremin. The theremin is an electronic instrument that you can play without touching it.

If I move my hand closer to this antenna, the pitch of the sound will change. And if I move my hand closer to this other antenna, the pitch will go up, and over here... closer and farther away from this one I can control the volume. It’s like magic... but it’s all based on electricity.

Sound is produced when something vibrates - which makes the air vibrate, which makes our eardrums vibrate, which our brain interprets as a sound. With guitars, of course, the vibrating part is the string. And with electronic instruments, it’s an electric current that causes a speaker to vibrate. So we need to make electricity flow back and forth, which is what’s called an alternating current. And perhaps the most important component to make that happen is a capacitor.

A capacitor is a device that can store an electric charge. It’s made up of two plates that can conduct electricity, with something in-between them - whether it’s air or another material - called the dielectric. When there’s an electric current, electrons want to flow between the plates, but they’re blocked by the dielectric. So instead, the electrons get stuck on one side of the capacitor. And the electric charge - negative on one plate and positive on the other - keeps building up.

With the right setup, those stuck electrons eventually change directions, head down the wire, to the other side of the capacitor. This pattern continues, with the electrons going back and forth to create an alternating current that oscillates at a certain rate, or frequency. And that’s what’s going on in a theremin. Sort of.

The thing is, the theremin doesn’t have a whole capacitor in it. Instead, the theremin just has one plate of its capacitor, which is this antenna here. The other plate of the capacitor is my hand. So the theremin and I - plus the air between us - work together to make a full capacitor, which means I control the oscillations of the current!

When I move my hand close to the antenna, the capacitor’s plates are closer together, so it stores more charge, and the current oscillates at a lower frequency. And when I move my hand further away, the capacitor’s plates are farther apart. Here, it stores less charge, and the current oscillates at a higher frequency. Now this current has the the ability to vibrate a speaker and create sound waves. But first, there’s one final obstacle we have to overcome.

The current would have a frequency of around 250 kilohertz, which is way above what humans can hear. So we can’t send the current straight to the speaker. Instead, the theremin does something called heterodyning. Heterodyning is when you mix two currents together in order to change their frequencies. In the theremin, we mix our oscillating current with another pre-set current - this one’s being produced inside the theremin and can’t be easily interfered with. During heterodyning, these currents mix together to produce a final current with a human-friendly frequency - typically within the range of a piano. As a side-effect , this mixing process actually switches the order of the frequencies - higher becomes lower, and lower becomes higher.

So, you’ll notice that the speaker produces higher notes if your hand is closer to the theremin, and lower notes if your hand is farther away. At long last, the current is ready to be amplified and sent to speaker. The speaker then vibrates the air to make sound waves. A similar process happens with the volume control, except that the theremin converts the frequencies into volume, rather than pitch. And now you can make music... without even touching an instrument! It’s all possible with just a few simple electronic devices.

Thank you for watching this episode of SciShow, which was brought to you by our patrons on Patreon. And thank you especially to Jay Bruns of nojayart.com for lending us your theremin. If you want to help support our show, you can go to patreon.com/scishow. And don’t forget to go to youtube.com/scishow and subscribe!