Step 1: Materials
What you will need:
- Scrap Wood or another material for a base
- Electromagnets, I pulled the ones you see from a broken CD drive
- Magnets, the smaller round magnets are pulled from magnetic ball and stick toys from the dollar store, and the two larger ones from a CD drive
- Plastic, such as from many electronics packaging
- Cardboard, such as from a cereal box
Step 2: Prepare the Base
The first step is to cut four grooves as shown in the picture. The purpose of these is to hold the plastic rectangles under pressure, so the vibrations better resonate in the plastic.
You will want to make the cuts about 3mm deep and about 7-8 cm apart for each speaker. This is just enough for the plastic edges to catch hold.
Step 3: Add the Plastic Sheets
Cut the plastic rectangles about 8.5cm long and the width of the groove in the base. Just in case, cut too much so when you fine tune it you can cut the extra off.
The plastic is cut longer then the grooves are apart so it bows up about 1.5 cm in the middle, where the electromagnet will sit.
To get the sheets to stay in place, use pliers to bend a lip downward on each end of the rectangle, about the depth of the groove in the base.
Step 4: Add the Electromagnets
For this step all you need to do is tape the electromagnets to the base, so that they won't interfere with the plastic moving. Also so the side of the coil is in the middle of the speaker. Why will be explained later.
Step 5: Add the Magnets
To add the magnets, simply take one smaller magnet ind place it in the center of a plastic sheet from earlier.
Next you will need to add a stack of smaller magnets under the sheet so they are held in place by the magnet above the sheet. Be sure to add the largest magnet on the bottom of the stack.
The size of the stack will depend on your speaker, the point is to get the larger magnet close to the electromagnet without touching it.
Next place the ends on the plastic sheet in the corresponding grooves in the speaker base, as shown in the picture.
Step 6: Fasten Everything in Place
Take strips off the cardboard about the depth of your groove. The purpose of these is to buffer the plastic from buzzing on the base.
Take the strips and push them into the grooves alongside the plastic. Once you have it in place, tape the end down so nothing will move. Be sure to leave extra tape to be trimmed off later.
You will want to put some tape over the edge of the speaker to reinforce it, as seen in the pictures below.
Step 7: Power It!
The final step, add the amplifier to the speakers.
For my amplifier I used an H-bridge motor driver, good to 1A at 36 V.
For my music source I used an Atmega168 using PWM to generate sound.
There are many good instructions on the internet on how to build amplifiers, so I won't bore you with more details.
Step 8: The Physics (aka. the Fun Part )
These speakers work by the magnet being forced side to side, rather then up and down. This is done by placing the magnet over the wire itself instead of over the center. So when an electric field is generated, and comes in or out of the center of the coil, it loops around the outside of the coil and the magnetic field of the permanent magnet is either repelled or attracted side to side by the electromagnet. This causes the magnets to move and the plastic flex, creating sound!