Build Your Own Speakers

Introduction

1. Electricity
   • What exactly is electricity? We hear this word all the time. Computers use electricity. Power plants make electricity. The word is so prevalent in our lives now, that for many of us, it’s one of life’s givens. We just don’t sit down and think, “what exactly is electricity?”
   • Electricity is a flow of electrons (aka current) around a circuit.
   • Demo: Do the snap circuit demo explain how electricity will flow through the wires and power the lamp. How the battery provides the electric pressure to push the electrons from one end of the battery to another. How if the circuit is broken, electricity won’t be able to jump the gap. A highway/car analogy would be nice.
   • Hopefully you have an general idea, and let’s start looking at the real thing. If we are going to build an electric circuit from scratch, we will want to control where and which way it flows. The wire is just like the riverbed, it allows the electrons to flow through it. A battery is just like a water pump, it will controls which direction the electrons will flow in.
2. Magnetism
   • Here’s another question. What exactly is magnetism? Many of our minds probably head towards this imagine of a horseshoe magnet or maybe an image of a bar magnet. All of these magnets have a specific direction to them. These directions are called the north pole and the south pole. Magnets will attract each other when opposite poles are nearby. They will repel each other when similar poles are nearby.
   • Would you be shocked if I told you that we could make a magnet just like those stuck on your refrigerator with clever use of electricity and wires? In fact, magnetism is generated when current flows through a wire! Most of the time the magnetism isn’t not noticeable, but if we coiled a wire over and over like a spring, we can make the magnet strength stronger. The magnetic effect would be strong enough to affect other magnetic material. This is basics of an electromagnet!
   • So what makes an electromagnet so special? For one, a regular magnet can’t be turned on or off. You can’t tell it to attract that nail over there, then tell it to not do it anymore. It’s going to attract it whether you like it or not. An electromagnet can be turned on or off. When a current is flowing, it acts as a magnet. When a current isn’t flowing, it doesn’t. Another reason, an electromagnet can change it’s strength depending on how strong the current flowing through the wires is. A strong current would make a strong magnet and a weak current would make a weak magnet. Finally, and perhaps the most important part of an electromagnet, the north and south poles of an electromagnet can change whenever you change the direction of the current. When current is flowing one direction, it creates a magnet (say) with north on top and south on bottom. However, if we flipped the direction of the current, it now creates a magnet (say) with south on top and north on bottom.

Procedure

1. Prepare enough tape for your speaker by taking about 1 foot of tape and putting it aside.
2. Grab 1 long (0.5 x 11 inch) strip and a marker. Wrap the strip around the marker to make a cylinder 0.5 inch long. Cut some tape, and tape the paper so it doesn’t unravel when you let go. Picture to the right.
3. Cut a wire ~15 feet in length. Leave ~2 feet of extra wire before you start, then start coiling the wire tightly around the paper cylinder at least 50 times. You’ll want to try to coil the entire length of the cylinder, but coil itself over so as to prevent it from unwinding. Leave ~2 feet of extra wire on the other end.
4. Cut some tape, and tape the coil around the paper cylinder to hold it in place.
5. Tape the paper cylinder to the bottom of bowl, as close to the center as possible. Picture to the right.
6. Take 2 Manila folder strips and fold them hamburger style like a paper fan. Fold it one or two more times so it resembles an accordion. Then tape them onto the bottom of the bowl as parallel and symmetrical as possible. Picture to the right.
7. Tape a magnet to the middle of the cardboard base. Stack the rest of the magnets on top so they magnetically attach.
8. Flip the bowl upright and fit the magnets in the coiled cylinder.
9. Fold, move, or cut the accordion strips so that the bowl is balanced, is free to move, and has at least half the magnets in the coiled cylinder.
10. Tape down the supports onto the cardboard base. The plate should be parallel to the cardboard base. Picture to the right.
11. Get a small piece of sandpaper, and strip about 0.5” from each end of the wire. You can do this by gently sandwiching the wire with the sandpaper and gently pulling the wire away. You’ll notice the red enamel of the wire slowly disappear revealing the copper underneath.
12. Get a battery and test the speaker by touching the loose ends of the wire to the ends of the battery. The speaker should move. If it doesn’t then try removing more enamel from the wire or loosening the cylinder from the magnets.
13. Thread the two loose ends of the wire through the audio plug sheath. Then fit the wire into the audio plug holes. With the help of PiE staff, solder the ends to an audio connector. Picture to the right.
14. Test it out with your mp3 player or audio device by plugging the aux jack into the audio plug!

Discussion

Sound
You’ve just built a speaker, so it’s important to know what sound is and how it works.
Sound is the compression and expansion of a medium like water or air. When you listen to someone talk or sing, its the person’s vocal cords that vibrate, manipulating the flow of air. The same occurs when an instrument is played. The instrument’s material, like a drum head, vibrates, compressing air. When the air gets to your ear, your ear has special equipment that allows it to translate the rate at which these compressed air molecules arrive. If the drum head is vibrating quickly/slowly, compressing the air at a quick/slow rate, it is associated with a high/low pitch.

EM to Sound
Finally! How does this all connect with each other? Let’s think about this like an engineer!
The electromagnet is taped to the bowl. When current flows through the electromagnet, it acts just like a regular magnet. As the electromagnet turns on, turns off, or switches direction, it is attracted or repelled to the magnet taped to the cardboard base. (When you use the speaker, can you see the oscillations?) This results in the oscillation of the bowl, the compression of air, and thus sound is made.

Extra time

1. What genre of music does your speaker play the best? Classical, rock, electronic, pop, or hip hop? How about artists? Beethoven, AC/DC, Daft Punk, Rihanna, or Jay-Z? Try putting on your scientist cap on, make a list, and rate them 1-10.
2. What do you think would happen if you changed some of the materials? What if you used less magnets? More magnets? Less loops of wire? More loops? Do you think paper or styrofoam is better? What about a plate instead of a bowl? We encourage you to think about all these things, come up with a hypothesis, and even test it out! The instructions to build the speaker will be the same, just change that little bit you want to test.
3. These speakers also work as microphones. If you plug it into a computer’s microphone port and use a sound recording program like Audacity, you can get a decent recording of yourself if you talk loudly into the speaker. Try it out! Why do you think this works? (Hint: Think of EM to Sound)
4. Now we’ve learned how speakers work. All it took was learning seemingly unrelated scientific subjects and applying them together. We encourage you to look at more things taken for granted like a clock and learn what makes it tick. Soon enough, you’ll find science everywhere!

Resources