Engineering Inside:

2014 Issue 2
Music

Build Your Own Speakers

June 2014

by Robin Hegg

Speakers are in all sorts of objects you see and use every day—stereos, telephones, moviespeaker theaters, concert halls, iPods, and more. Speakers work by turning an electrical signal into a sound you can hear. Speakers contain an electromagnet (a magnetic coil that creates a magnetic field when electricity flows through it). An electromagnet’s poles can be reversed depending on the direction of the current in the coil. In a speaker, the electromagnet is placed next to a (regular) permanent magnet. As electricity flows through the coil of the electromagnet, its poles change rapidly, alternately attracting it to and repelling it from the permanent magnet, causing it to vibrate back and forth. A cone is attached to the magnets that amplifies the vibrations, sending sound waves into the air.

Activity #1: Make Your Own Speaker With a Styrofoam Plate

In this activity, you can create your own speaker by creating an electromagnet and using a Styrofoam plate as your cone. Please have an adult help you when attaching wires and plugging in your speaker.

If you have trouble finding the materials for this activity, a second, simpler activity (Paper Cup iPhone “Speakers”) is available at the bottom of the page.

Materials

  • Two strips of paper, ½” x 11” each
  • Neodymium magnets, small, enough to create a small cylinder
  • Flat square of cardboard, larger than the plate
  • Audio plug
  • Glue
  • Tape
  • 2 business cards
  • Copper wire, 32-gauge, enameled
  • Styrofoam plate
  • Ruler
  • Scissors
  • Wire cutter/stripper

Steps:

  1. Roll one strip of paper lengthwise into a coil around the magnet and tape the roll of paper closed.
  2. Roll the second strip of paper around the first one and tape it closed as well. One roll of paper should sit snugly inside the other, but they shouldn’t be attached.
  3. Remove the magnet from the rolls of paper.
  4. Glue the paper cylinders onto the back of the plate, positioning them right in the center. Once the glue has dried, put the magnet back inside the cylinders.
  5. Leaving some extra wire length at each end, wind the wire around the cylinder about 50 times. When you’ve finished winding the wire, secure the wire coil with tape.
  6. Remove the magnet from the cylinders. Then remove the inner paper cylinder. It’s okay if the inner cylinder tears, but it’s important not to damage the outer cylinder.
  7. Fold the two business cards accordion-style widthwise, creating W shapes.
  8. Glue one end of each business card to the back of the plate so the cards are parallel to one another and stick up on either side of the cylinder.
  9. Return the magnet to the cylinder.
  10. Put some glue on the ends of each business card. Place a little glue on the magnet as well, making sure it’s not enough to touch the inside of the cylinder.
  11. Position your piece of cardboard on top of the speaker, with the plate underneath. The cardboard will serve as your speaker’s base. Flip everything over so the cardboard base is on the bottom and the plate is facing up. The magnet should fall down and glue itself onto the cardboard base. Push the glued ends of the business cards onto the cardboard to help support the plate and the cylinder. You want the cylinder to hover around the top of the magnet.
  12. Make sure the two wire ends of the coil are separated and aren’t touching anything.
  13. Cut and strip the wires from the audio plug and connect them to the coil.
  14. Allow all the glue on your speaker to dry.
  15. Your speaker is ready to use! You can plug it into your mp3 player, computer, or phone and give it a listen.

Troubleshooting

  • Make sure the business cards are parallel. You can try gluing them closer to or farther from the coil until you find the distance that produces the best sound.
  • Check that the coil is tight and secure and that nothing is touching the loose ends of the wire.
  • Make sure the business cards are glued on completely and that they are the only things touching the foam plate.
  • The coil shouldn’t touch the magnet or the base of the speaker. If it does, try making the coil wider or fold the cards more loosely so they hold the speaker further from the base.

Activity #2: Paper Cup iPhone “Speakers”

This activity creates a “speaker” system for your iPhone or iPod. The “speaker” works by using the cone shape of plastic cups like an acoustic horn (or megaphone) to amplify the sound coming from your phone’s speakers.

Materials:

  • Two plastic cups
  • Paper towel roll
  • Scissors
  • Pen or pencil

Steps:

  1. Use the scissors to cut three sides of rectangular hole in the paper towel roll for your iPhone to fit into. Leave one of the long sides attached so that the flap can support the back of your phone.
  2. Using the ends of the paper towel roll, trace circles on the sides of the cups using a pencil or pen. Cut the circles out of the cups, creating two paper towel roll-sized holes.
  3. Insert the paper towel roll into the cups.
  4. Place your iPhone into the slot you cut in the paper towel roll and press play. Listen to the sound come through your “speakers”!

Questions:

  1. Why do you think the cone shape of speaker cones (like the Styrofoam plate or the plastic cups) matters in speakers?
  2. Do you think the material your cone was made of makes a difference in the sound that’s produced? Why or why not?
  3. In the Styrofoam plate activity, why do you think it was so important that the paper cylinder hover above the magnet and not touch the base of the speaker?

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