Electromagnetic Fun: How to Turn a Styrofoam Bowl into a Speaker

If your child loves making science projects, here is a unique idea that is certain to catch his/her interest!

Styrofoam Speaker

Here is the finished speaker my 10 yr. old son made (with a little supervision)

Materials:

  • One styrofoam bowl
  • One paper plate
  • Hot glue gun
  • Scissors
  • 10 Neodymium button magnets (regular button magnets will work too, however, your speaker will not be as loud. Neodymium magnets can be bought online.)
  • One sheet of printer paper
  • Magnet wire (it MUST be enameled copper wire)
  • Oven gloves
  • A piece of sandpaper
  • Stereo with amplifier

Safety Notes: Do not get the magnet wire from an old tv. You could get a shock trying to take it out. The glue gun and the glue can burn you. Wear oven gloves before picking up the glue gun.

Instructions:

1. Stack 6 Neodymium button magnets to make a cylinder.

2. Cut a strip of paper that is just wide enough to cover all of the magnets (not the ends of them, however), and long enough so you can wrap it around the stack until the edges meet, then tape it closed.

3. Cut another strip of paper just large enough so you can wrap it around the first piece, and tape it closed. The two pieces of paper should not be connected to each other. Each piece should be able to move up and down independently.

4. Wrap the magnet wire around the tube snugly (but not too tight) fifty times.

5. Use the glue gun to glue the wire in place. Pull the stack of magnets and inner strip of paper out of the tube, and you should now have an empty tube with wire wound around it. This is going to be the voice coil.

6. Make sure the voice coil will slide over the magnet stack. If not, you can cut the voice coil shorter. Take the magnet stack out of the voice coil.

7. Use the glue gun to glue the voice coil to the bottom of the paper plate.

8. Cut out the shape of your speaker in the bowl (see above photo — cut out three large trapezoid shapes evenly spaced apart.)

9. Use the glue gun to glue the magnets inside the center of the bowl.

10. Slide the voice coil over top the magnets.

11. Remove the coating from the tips of the wires (sandpaper works well.)

12. Hook your speaker wires up to a stereo that has an amplifier, and crank it up!

Optional: For extra fun, pour water onto the plate. The vibrations will make the water dance and splash!

Dancing Water on Speaker

Challenge your child:

After you’ve created a working speaker, try experimenting with the number of magnets, the amount of wire, or the size of the diaphragm (a larger/smaller styrofoam bowl) to find out how it affects the sound. However, make sure you only change one variable at a time. These experiments would lend themselves nicely to a science fair project!

Also, add an educational aspect to this project by having your child further research the progression of scientific knowledge that led to the invention of the loudspeaker, and/or the scientific principles behind this project.

Helpful background information:

The speakers that people use for listening to music are called electrodynamic loudspeakers. Even though electromagnets were invented in the 1860’s, it still took forty more years before anyone figured out how to make a speaker. C.W. Rice of General Electric and E.W. Kellogg of AT&T finally figured out how to make the shape of the diaphragm and what materials would be needed to make the speaker. In 1910, vacuum tubes were invented, and were used to control the frequency of the sound coming out of the speaker.

Speakers turn electricity into sound. They are made by putting a metal coil of wire near a magnet. When electricity flows through the coiled wire, it is either attracted or repelled by the magnet, and this magnetic field causes the metal coils to move. The coiled wire is connected to a cone made out of paper or cardboard. This cone is called a diaphragm, and when the coils vibrate, it does too. The vibrations push on a large amount of air and make sound waves. The sound comes out of the diaphragm and is made louder because of its cone shape. Making sound louder is called amplification.

Sound is a type of energy that goes through gas or liquid in waves. The two major ways to measure sound are with frequency and decibels. Decibels measure how loud the sound is that is coming from a speaker by measuring sound pressure. Frequency measures the quality of the sound coming from the speaker. It tells how high or low the sound is. Some speakers use different sized cones so the high, medium and low frequencies can be heard.

References:

“Alternating-current” Kids.Net.au http://encyclopedia.kids.net.au/page/al/Alternating_current

Whelan, M. “History and Types of Loudspeakers” http://www.edisontechcenter.org/speakers.html

“How Do Speakers Work?” Institute of Physics http://www.physics.org/article-questions.asp?id=54

“How to Make a Paper Plate Speaker That Actually Works for Under $1” http://science.wonderhowto.com/how-to/make-paper-plate-speaker-actually-works-for-under-1-0141522/

I have been a teacher, an educational trainer, editor, and freelance writer, but my most important job of all has been that of a wife and mother. I love spending time with my husband and 3 children.

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