How To: Make a homemade pair of headphones using a voice coil, magnets, and diaphragm
Step 1: Material List
- 2 strands about 250 cm long of 28 gauge copper wire (it can be thinner as long as it is light enough to move and vibrate in the speaker)
- Wire cutters (or regular scissors capable of cutting 28 gauge copper wire)
- 2 paper Dixie cups cut to 2.5 cm tall with a diameter of 5 cm
- 2 plastic cups that are equal to or less than 2.5 cm tall and 5 cm wide
- 2 styrofoam cups cut to 5.75 cm high and with diameter of 6.5 cm
- 8 neodymium magnets permanent magnets with a diameter of
- Roll of electric tape or scotch tape
- Pair of old earmuffs or headphones with pads on them
- 3.5 mm stereo jack
- 6 by 6 square inch piece of sandpaper
- Package of tin foil
- Liquid glue (you can also solder instead of using glue)
- Old headband
Gather all materials listed above. They can be found at supply stores like Home Depot if you don't already have them.
Step 2: Assembly, Sanding, and Coiling
- Grab one of the 250 cm long copper wires
- Start making the main parts in the speaker by coiling the copper wire around a glue stick 65 times and keeping it secure by using the tape or by wrapping it around itself. The tape should be able to stop it from unraveling but wrapping it around itself will work too. Leave about 90 cm on one end and 20 cm on the other end.
- Sand about 5 centimeters off of the copper wire ends
It is necessary to sand the wire because it will make sure the current can flow from the audio source to the wires as well as from wire to wire. If we did not sand it, the wire could not conduct the current since it would be covered in an insulator/resistor. An insulator is something that does not allow the current to flow through it. With the insulator on the wire, it is basically a barrier to keep the electricity from flowing through it. The current is what starts the system in the headphones. If electricity cannot flow through the wire, then it will not reach the magnet and the voice coil will not be able to vibrate and produce sound.
You can use the right hand rule to see what direction the magnetic field is going in by pointing your thumb in the direction of the current and then encircling your fingers around the armature. The armature is the coil of wires, which is also known as the voice coil in speakers. You will be able to see where the magnetic field is pointing and where the current is going.
We chose to coil 65 times because in prototyping, we heard that the more coils we wrapped, it made the sound louder. 60-75 coils is a good number. Too many coils or too few coils did not produce good sound. This is because if we chose to wrap around more coils, we would need more magnets or stronger magnets and no sound will be produced. If we chose to wrap less, the coil would not be able to produce a strong magnetic field. We chose a 28 gauge wire because the thinner the wire is, the easier it is to vibrate and produce sound. The coil becomes a temporary magnet when electricity flows through the wire and attracts and repels with the permanent magnet. The current through any conductor creates a circular magnetic field around the wire.The more winds of coil increases the strength in a magnetic field current. The current that flows through the wire passes through the center of the coil causing it to become a stronger field. The voltage can be increased by winding more wire coils because the field lines intersect the current many times. If the fingers are wrapped around the magnetic core of a coil in the direction of the current through the wire, the thumb will point in the direction the magnetic field that pass through the coil. The strength of the magnetic field around the coil can be increased by:
1. Using a stronger magnet
2. Using more wraps of wire in the coil
3. Using a thinner conductor. If the magnetic field is stronger, it will also make the vibrations stronger and therefore make the sound quality clearer and louder.
Step 3: Magnet Positioning and Diaphragm Assembly
- Take the coiled wire (also called the armature) and put the coil on the bottom of the paper cup. Then, put two magnets in the center of it. The magnets should not rise above the coil. If it does, take out one of the magnets, add more coils, or do both until it is only in the middle of the coil.
- Put the other two magnets in the inside of the cup so it is attracted to the ones on the bottom.
- Secure the voice coil and magnets to the bottom of the cup by making an “X” with the electrical tape over it. Be sure to leave the sanded ends exposed with enough on one end to be about .
- Connect one of the copper wire ends to the one of the terminals in the aux plug. They can not be touching and have to be secured.
- Repeat the procedures in Step 2 and Step 3 to make a second speaker for the other ear. The only thing you will change is instead of wrapping the wire on only one terminal, you'll wrap it one both of the terminals on that one side.
The permanent neodymium magnet is used for attracting and repelling with the voice coil in the magnetic field. The voice coil serves as a temporary magnet after it has current flowing through it since it is an electromagnet. This means it will become magnetized if enough electricity is running through it. If the current stops flowing, the coil is no longer magnetic. The current switches directions which switches the poles in the magnet to make it repel and attract the coil to the permanent magnet. This movement produces the vibrations for sound.
The magnets have to be in the coil so its magnetic field can reach around the coil and make it vibrate when it is attracted and repelled. We learned that the stronger/more magnets there are, the clearer the sound is. We also learned from research that the diaphragm should be a somewhat dense material so vibrations can still travel through it but not override the sound and produce static noise. Instead of using just one dense material, we decided to use all three materials starting with the paper cup which is dense, the plastic cup, and then the styrofoam cup.
We chose 8 magnets in our speaker because we wanted our headphones to have a better bass quality, and we could hear in prototyping that increasing the number of magnets improved the quality of the bass.
Step 4: Plug and Play
- When you sand the ends, it is quicker and easier if you wrap the sandpaper around the wire and scrape the insulator off the wire to make sure the copper wire is exposed.
- Take the ends of the wires that are not connected to the terminal and connect them to each other by wrapping them together. Make sure it is touching the sanded parts.
- Take that same wire that is connected and wrap it in the tinfoil around the headband leaving none of the wires exposed.
- After that, wrap the rest of the two wire ends that are connected to the auxiliary plug.
- Secure the wires connected to the aux plug in any way you can such as soldering it or taping it. You can also solder the other ends that are sanded down.
- Lastly, you can wrap the visible wires in tinfoil, connect it to the headband, and/or use play-doh as an insulator where the wires are sanded.
Once again, you need to sand the ends of the wires before you connect it to the aux plug so it can allow the current to flow from the audio source and through the wire. If it is not sanded, the resistors and insulators will stop the electric signals from passing through the wire and reaching the temporary magnet to make it move back and forth. Those vibrations from being attracted and repelled push the air at different speed to create the sounds that we hear.
The alternating current is able to make it repel and attract at exact times to create certain sounds or music. Using the aux cord connects the speaker to a phone or computer which will send the alternating current to magnetize the voice coil. The alternating current is important because it makes the current travel in both directions to switch which way the pole is pointing. It starts from the aux plug where it gets the electric signal and goes through the electromagnet causing the voice coil to vibrate the diaphragm. We observed that the stronger the magnets were, we could hear that the lyrics were clearer. However, the more coils we added, the louder the music was. The way the sound waves are produced is due to the electromagnet moving up and down when it is repelled and attracted to the permanent magnet. The movement causes the air to be pushed at different speeds, and also causes the diaphragm to vibrate. The air being pushed/moved, along with the vibrations are the factors that create the sounds.
Usually during prototyping, the bass was overpowering the lyrics and high pitches and making it sound like there was some background noise. We heard it a lot on songs that had a strong bas; on songs that were high pitch, we could easily understand the lyrics and hear the music without outside noise so we concluded that the speaker we made does not work as well with songs that have a low bass.
Step 5: Troubleshooting
- Lastly, test the headphones by plugging the aux plug into a phone or computer and play music. If it does not work, try going through the steps again and make sure that the voice coil, magnets, and wires are properly connected (it can not be loose), completely sanded, and not touching wires or terminals that they should not be connected to. If you can’t hear music from the headphones, check where the aux is connected to the phone. Push it in all the way into the phone and check that the wires are wrapped to the aux plug and are not touching either one wire or the other since that causes the current to stop. If that still does not work, try to go through each of the steps again and see if there is a step that you did wrong or forgot to do.
- To make it more comfortable, you can glue ear-pads from old headphones to the end of the styrofoam cups for when you use the headphones.