You'll be amazed how easy it is to make reasonable sounding headphones for a few dollars in parts. While a Styrofoam bowl isn't going to sound quite as good as some Beats by Dre headphones, most people who listen say "wow, I never would have expected that from a bowl and a plate!"
This is a good school science activity (electricity, magnetism, sound waves, etc.) as long as there is adult supervision for both safety and coaching. Kids at our local school had fun making these, putting stickers on them, working with a friend to make a pair, etc. You can pass out the URL http://tinyURL.com/make-headphones
What you'll need:
- 6" diameter Styrofoam bowls (qty 2).
- Available on Amazon in a 100 pack.
- 6" diameter Styrofoam plates (qty 2).
- Available on Amazon in a 100 pack here.
- Sheet of paper, 8.5"x11" (qty 1)
- 1/2" x 3/8" Neodymium magnets (qty 2) [1/2" x 1/4" is OK].
- Available on Amazon.
- Huge quantity available here.
- For one headphone, available here.
- Wire strippers / cutters.
- Available on Amazon.
- Soldering iron and solder (optional, but makes it last longer)
- Needle nose Pliers
- Paper cutting tool
Step 1: Theory
A loudspeaker is made out of the following parts:
- A diaphragm (also called a cone) that moves and pushes air creating sound waves
- A voice coil (an electromagnet) attached to the diaphragm. Alternating electricity from an audio device creates an alternating magnetic force towards or away from the permanent magnet.
- A permanent magnet that is fixed to a base so that it doesn't move, with the moving voice coil coaxial with it.
- A suspension that holds the diaphragm and voice coil in place around the fixed permanent magnet, but allows the diaphragm and voice coil to move towards and away from the permanent magnet.
- A sturdy base that the permanent magnet and suspension are fixed to.
Step 2: Voice Coil - Outer Strip
To make the voice coil, cut your 8.5"x11" sheet of paper the short way into two 1 inch wide strips.
You can use a paper cutter to get a perfect straight edge, or you can use a ruler and scissors to make a perfectly straight 1" wide strip (1" x 8.5").
Step 3: Voice Coil - Spacer
Repeat for a second 1" x 8.5" strip.
In the picture ignore the 3rd narrow strip, you don't need it. That was for an advanced feature that didn't help the sound so I've deleted it.
You should have 2 strips, each 1 inch wide by 8.5" long.
Step 4: Voice Coil - Roll the Spacer
Take your magnets (you can join several if it helps) and tightly roll one of the paper strips around the magnet.
Then use just enough "scotch" tape to hold the strip roll in place.
Be careful that your roll is lined up and straight.
It should be snug, but loose enough that you can still get the magnets out later (don't take the magnets out yet).
Step 5: Voice Coil - Outer Coil Roll
Now roll the second 1" wide strip of paper around the first roll.
Tape it with just enough "scotch" tape to hold.
Make sure it is snug, but not so tight that you can't get the inner roll out with a tool later.
Make sure it is straight and aligned into a perfect cylinder.
Step 6: Voice Coil - Prepare to Glue
Now slide the maget(s) completely out of the inner roll.
Slide the inner roll (the spacer) 1/3 of the way out of the outer roll (the voice coil).
DO NOT REMOVE the inner roll yet. Look at the picture.
We need the inner roll to be out of the way so that it doesn't get glue on it in the next step, but we still need it for structural support.
Step 7: Glue the Voice Coil to the Plate
Place the voice coil at the center of the plate with the inner spacer sticking up.
Using a hot glue gun, glue the outer voice coil roll to the center of the plate, being careful not to get any glue on the inner spacer roll.
When the glue is still hot, gently nudge the voice coil so that it stands straight up on the plate (no leaning).
Let the glue completely cool. You can blow on it to speed up the cooling.
Step 8: Voice Coil - Wind the Coil
- Once the hot glue is completely cooled and not tacky to the touch, push down the inner spacer roll of paper to act as a structural support.
- Take several feet of your magnet wire and extend it off the plate. This will be your headphone cord and needs to be long enough to reach your audio device.
Hot-glue (or tape) the the magnet wire where it meets the plate (the side that isn't going to the spool of magnet wire)
- Now carefully wind (loop) the magnet wire around the paper voice coil roll.
- Try and make each winding snug against the side of the prior winding.
- After you make a loop, put your thumb on the prior windings to keep them from unraveling.
- Use snug but NOT tight pressure. You don't want the paper roll to collapse.
- Count each winding loop. You want at least 150 turns of the wire. (Any number between 150 to 200).
- Eventually your side-by-side winding's will approach the edge of the paper voice coil roll. You want to come about 1/8 of an inch away from the edge and then reverse direction of you winding loops. In other words, your new loops of wire will overlap with your prior windings. You'll be making layers of windings until you count to 150.
- Once you overlap the windings, it is hard to make each loop nice and neat side-by-side with the prior ones. Don't worry. It can be messy and work fine. Just try your best to have the windings overlap as evenly as you can as you work your way back towards the plate, and then back towards the end of the paper roll, etc.
Step 9: Finishing the Voice Coil
To finish the voice coil:
- Put a thin layer of hot glue over your magnet wire windings. You want to minimize the mass (the weight) of the voice coil for good sound, but you don't want the wires to shift or unravel.
- Some hot glue should go near the end of the paper roll right where the magnet wire loops end to hold the wire in place. DO NOT GET GLUE IN THE PAPER TUBE, NOR AT THE TOP EDGE OF THE PAPER.
- Wait for the hot glue to cool. Blowing on it helps.
- Use your pinkie or needle-nose pliers to pull out the inner paper roll spacer. If it is stuck, try grabbing the inside edge of the paper and twist it inward as you pull out. Throw out the spacer - we only needed it to provide support when winding the wire and to create a gap between our permanent magnet and the voice coil (they shouldn't rub or touch).
Step 10: Prepare the Base
Cut a hole in the side of the bowl so you can see inside.
Note that this step is optional - once built, it allows the kids to see how a speaker works inside. It is the "window of truth!" It also helps immensely with assembly.
Step 11: Prepare to Align the Magnet
- From the scrap Styrofoam you cut out in the previous step, rip off a tiny bit that you can drop down the voice coil tube. The purpose is to keep the magnet from sticking to any of the no-longer-hot glue inside. If your glue isn't tacky at all, you can skip this step.
- Drop your magnet down inside the voice coil. It should not stick to the sides nor the bottom. (You did remember to remove the spacer strip of paper, right?)
Step 12: Position the Magnet
- Place the plate with the voice coil pointing straight up, with the magnet inside the tube.
- Unlike how you see it in the picture: do NOT snake the magnet wire ends through the hole you cut in the bowl. Rather just let the magnet wire go between the plate and the bowl for now. We'll snake the wires through the hole in a later step after the magnet is glued.
- Place the upside-down bowl onto the plate and center it. If you purchased a 6 inch diameter bowl and 6 inch diameter plate they should mate perfectly
- While slightly squeezing the center of the bottom of the bowl towards the voice coil of the plate, turn the bowl-and-plate right-side-up together as a unit.
- Your magnet should now have fallen down the voice coil and should be sitting in the exact center of the bottom of the bowl
- VERY CAREFULLY lift the plate STRAIGHT UP so as not to move the position of the magnet. We need the magnet's position to align with the center of the voice coil
- Use your finger to hold the magnet in position without shifting it
- Use a pen to mark the exact location of the magnet.
- Remove the magnet and put a small dab of hot glue in the center of your markings.
- Push the magnet into the center of the hot glue and let it cool.
Step 13: Assemble the Diaphragm to the Base
- WAIT FOR THE GLUE TO COOL. IT MUST NOT BE TACKY.
- Snake the magnet wire ends through the hole in the bowl.
- Put the plate and bowl together again and make sure that the voice coil goes over the magnet and that the sides of the voice coil don't rub against the magnet. The voice coil needs to vibrate up and down around the magnet.
- [It is very hard to get the alignment perfect so a little rubbing may still work, but it can't be tight].
- If you are happy with the alignment, then in a quick process (before the glue dries):
- Put 6 or so dabs of hot glue on the edge of the bowl
- Align the voice coil (without getting any hot glue "hairs" in the coil area) and
- Glue the plate to the bowl.
Step 14: Repeat for the Right Ear Speaker
- If you are making headphones, you now want to repeat all the prior steps to make another speaker for the other ear.
Step 15: Prepare Your Wires
- Use a match to burn off the lacquer insulation that covers the end of the magnet wire-- you just want to remove the lacquer from the last inch of the wire ends. Do this for each of the 2 ends to the magnet wire (4 ends if you've made two speakers; one for each ear).
- Take your 3.5mm stereo audio cable and cut it in half.
- Very carefully (this takes patience and practice, sorry-- you may have to buy several if you destroy yours) you want to remove the outer insulating jacket as shown. About 2 or 3 inches of the outer jacket insulation. The key is to cut the jacket while NOT cutting the wires inside. I do this by circling the jacket with the knife edge of my wire cutters several times with light pressure to make a deep score and then use the somewhat open jaw of the wire cutters to pull-snap off the jacket axially.
- Once the jacket is off several inches, you'll see 3 wires inside.
- Strip off a little more than 1/4" of the insulation of each of the 3 wires inside as shown.
Step 16: Wire It Up!
- Take the end one of the magnet wires from the left speaker and twist it with the end of a wire from the right speaker. This is the "common" wire of your speakers.
- There are 3 wires in your audio cable:
- One wire is "common" to both the left ear speaker and the right ear speaker. In my case the common wire is the red one. This will differ between manufacturers. With many companies, red often is the right ear wire and not common. Go figure.
- One wire is for the left ear signal. In my case that is my White wire.
- One wire is for the right ear signal. In my case that is the Yellow wire.
- Most people don't have a multi-meter or don't know how to use one, so you can find the "common" wire by trial and error:
- There are only 3 possible choices for the audio cable's common wire. So pick one, and attach the left and right wires to the remaining two wires. Hook up an iPod and crank the volume to max and listen to the volume.
- Do this for all 3 possible common wire choices.
- The loudest audio in both speakers at the same time will happen when you get the correct common wire.
Step 17: Insulate!
- To make the best electrical connection you'll want to solder the audio cable wires to the magnet wires for both mechanical strength and electrical connectivity. If you don't have soldering equipment or don't know how to use it, then just do a lot of twisting.
- Spread the 3 connections apart as shown
- Use electrical tape to insulate the 3 bundles of twisted exposed wire so that they can't electrically short (touch). You want to pull-stretch the tape slightly as you wrap it around the wires.
- Now use a longer bit of electrical tape to wrap the previous 3 bundles of electrical tape as shown.
Step 18: Finish It!
- Make a over-the-head band: using the remaining sheet of paper, fold it over and over lengthwise (so it is long).
- Tape the ends of the folded paper strip to the two speakers so that the wires exit the speakers from the bottom.
- Enjoy your sound!
Step 19: Extra Credit
An audio device headphone jack only produces a small amount of power, but it is enough for headphones that are very close to your ears.
For extra credit, if you want speakers that can be heard from across the room, you'll need an amplifier. In this case you would skip all the steps where you connected the magnet wire to the audio cable and instead hook the 4 ends of the magnet wire into a stereo amplifier. You could use your home receiver but you risk blowing your amp's transistors. A safer bet is to get a cheap audio amplifier for about $20 like this one on Amazon.
Or even cheaper (but lower power) like this (but takes advanced wiring) on Amazon.