The electromagnetic coil of this speaker is simultaneously the membrane that vibrates to make the sound you can hear. Woven on a circular loom made out of a paper cup, this speaker is definitely not very efficient, nor very loud. But it does look good.
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Step 1: Materials and Tools
* paper cup
* sewing thread
* conductive thread (use a highly conductive thread like Karl-Grimm copper)
* neodymium magnet(s)
* 3.7V lipo battery
* audio jack cable
* sound source
* measuring tape
* sewing needle
* scissors or snips
Step 2: Measure and Mark
Use a measuring tape to measure even spaces around the top brim of your paper cup. I chose 1cm spacing for my warp, but you can also try denser or sparser spacing. Denser spacing will result in a denser weave and will take longer to make. Sparser spacing will result in a looser weave, which will be quicker to make but if it is too loose you'll get spaces between the threads where the air can go through, so the vibrating membrane won't be as efficient at moving air and your speaker will be quieter as a result of this.
Step 3: Setting Up the Warp
The marks around the brim are where the warp threads will go. To make weaving easier, make sure your warp threads go OVER the edge of the brim to that they are plane with the surface.
Thread a sharp needle with some strong sewing thread. Start by sewing from the inside to the outside, leaving extra thread behind which we will use to tie a knot with the finishing end of the thread. Sew back and forth across the center of the cup as shown in the images. Getting this right is the most tedious part of the process.
Step 4: Weaving Conductive
Now the warp is ready to be woven. To weave between the wawrp threads you can use a sewing needle that is threaded with the weft thread, or you can make yourself a shuttle by cutting one out of an old credit card or similarly thick plastic. If you have a lasercutter and some acrylic to hand, this is also an easy way to make a shuttle. See attached file for a good shuttle shape.
Before you begin to weave, thread your conductive thread through a needle and sew it through the outside of the cup to the inside. Tie a knot in the end and pull until the knot hits the wall. This will be one of the two contacts to your speaker.
Now begin to weave by simply going over 1, under 1 of the warp threads around in a circle. This first round will look rather messy because you can't see the pattern forming. After the first 2-3 rounds it will become easy to see.
Step 5: Weaving Non-conductive
After starting with one full round of conductive thread, switch to weaving with a non-conductive sewing thread (you can also use yarn or string). Make sure your non-conductive thread is spacing the conductive thread apart so that it does not touch itself. If the conductive thread is insulated and touches itself, then electricity can flow from one part of the thread to the other and will not be forced to flow around and around in circles, which is what amplifies the electromagnetic field causing stronger vibrations as the electromagnet attracts and repels itself from the permanent magnet.
Step 6: Quick Test
At any point along the way you can pause and test your speaker. Simply clip the two output ends of the amplifier to either end of the conductive thread and play music through the amplifier. Listen closely. Even with only a few turns in your spiral you should be able to hear something. Because the length of conductive thread might not be very long, it might be TOO conductive and cause the amplifier to cut off. Try turning the volume down, or adding a 7Ohm resistor in series with your speaker spiral.
Step 7: Continue Weaving
Continue weaving for as long as you like. The more surface area you fill in, the bigger your membrane will be, the more air it will move, the louder it will sound.
When you've finished weaving, stitch the other end of the conductive thread to the outside of the cup and tie a knot.
Step 8: Play Music
Hook up your speaker and listen to it.
I have not found a nice way to mount the magnet close to the center of the woven electromagnet. I'm posting this Instructable in the hope that somebody will come up with a good solution for this.
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