Foam Plate Speakers

For science this week, we decided to experiment more with audio devices. (The episode of  The Joy of Science we had just watched was about properties of matter, including magnetism, and mentioned that speakers worked because magnets changed shaped.) Since we had already built a radio, this time we built a speaker. The speaker was much easier to make and much less elaborate than the radio, and we were able to have it working in about a half-hour. Despite requiring some fine-tuning, we were able to get it to work very well.

This simple and elegant project was designed by Jose Pino. You can see it being made in this Make Magazine YouTube tutorial.

We didn't test our speaker out with our foxhole radio, because the volume is so low on both devices. Instead we used an mp3 player. But we plan to try our homemade radio with the speaker sometime in the future.


Materials:

A foam plate
Two strips of paper
Two business cards (we just cut an index card in half for this)
Tape
A hot glue gun
Magnetic copper wire (Jose Pino recommends using AWG 32)
Neodymium magnets
An audio plug
A piece of cardboard

1. We started by rolling one of the strips of paper over the magnets. We then taped the roll closed, being careful not to tape it to the magnets.

2. Next, we rolled the other strip of paper around the first strip, and taped it closed. We cut this strip a little less wide than the first. This made the outer strip stick out a bit more than the inner one.

3. Keeping the magnet inside the tubes of paper, we coiled the copper wire around it, using about 50 turns. Leave a few inches of copper wire uncoiled on each end.

4. We then pulled the magnet out of our paper, along with the inner strip (we made it wider so that it would be easier to pull out.)

5. Discarding the inner strip, we then hot-glued the outer to the bottom of the foam plate, being careful to have it in the center.

6. Next, we hot-glued the magnet to the cardboard. After that, we folded the business cards in an accordion shape, we glued them to the bottom of the plate, one on each side of the coil. We then put hot glue on the bottoms of the cards, and glued them to the cardboard base, making sure that the coil would go over the magnet.

7. We tested the wires by touching the ends to either end of a battery. This is what happened:





8. To connect our speaker to a sound system, we needed an audio plug. We got one by cutting the end off a cheap set of earbuds from the dollar store. FIrst we had to sand off the coating from each end of the copper coil wire and strip the rubber insulation from the ends of the audio plug. Because the earbuds were stereo, we needed to connect one wire from each earbud to each of the copper coil wires in order to hear both sides. (We're not sure that worked well, though.)

9. Finally, we plugged the audio wire into a music device. We found that MP3 players worked the best.



How it Works:

The speakers operate largely on the same principle as the piezoelectric earpiece we used in our radio experiment. The coil serves as an electromagnet. It receives electrical currents from the audio plug, which gives it either a stronger or weaker attraction to the magnets. This causes the foam plate to bounce up and down, creating sound vibrations.