Embroider highly conductive thread to make a fabric speaker coil. Then run an amplified sound source through it and hold a magnet close to hear it play. Sewing the coil takes longer than you might think!
– Conductive thread
– 2 Neodymium magnets
– Fusible interfacing
You will need
– Sewing needle
– Regular thread
UNDERSTANDING HOW A SPEAKER WORKS
A speaker makes sound because an electromagnet (the embroidered coil) is mounted to a membrane (the fabric) with a permanent magnet close by. When an audio signal is connected to either end of the electromagnet (coil) a fluctuating magnetic field forms around the coil, repelling and attracting the membrane from the permanent magnet. These vibrations happen so fast that we can barely see them, but the membrane moves the air around it, translating electrical frequencies into audible waves that we can hear.
Take a good look at the diagram and stencil on the other side of this sheet so that you understand what variables will influence the efficiency (volume) of your speaker coil before designing your own.
TRACE AND FUSE
Iron a square of fusible interfacing to the back of the piece of fabric that you plan to embroider your speaker coil on. Peel the paper backing from fusible interfacing and trace the outline and mark the center point of your coil on the front of the fabric.
Fusible interfacing is a heat glue that bonds two pieces of fabric together, adding stiffness to the material. The reason it makes sense to stitch your speaker coil onto stiffer fabric is because it will help keep the fabric taut as you sew so that the coil will not start to collapse the fabric back on itself.
Either before or after sewing your speaker coil, use an iron to fuse your membrane to another piece of fabric, or an item of clothing, or your project – wherever you want the fabric speaker to go. Having multiple layers of fabric fused together does make it harder to sew, but it also makes for a stiffer membrane that is better at moving air.
With a sewing needle pull the end of your conductive thread through the center of your coil so that the needle ends up on the back side (with the fusible interfacing). Pull as much thread through as you will need to connect the center of your coil to your circuit. Generally 10-20 cm is good. Then remove the thread from the needle.
Thread the needle with regular thread and tie a knot in one end. Insert from the reverse side through the center point of your coil design. Stitch over the conductive thread and back into the fabric, then come back through the fabric a few mm further along your coil path. This embroidery technique is called “couching”.
As you are sewing your coil from center to edge, you want the conductive thread to come as close as possible to the previous turn without touching it. If one turn of the conductive thread touches another then the electricity will not be forced to flow around in circles, which is what increases the strength of the magnetic field.
For a quick first test of your speaker simply clip on two magnets one on either side of your coil, so that they hold each other in place. If you have a smaller magnet, then place this one on the front side, since the magnet is conductive it will otherwise short out your speaker’s coils. You can also put a piece of fabric in between the magnet and the coil to isolate it. For your final design you will want to mount your magnet(s) in the center of the coil without having them directly connected to the membrane.
HOOK UP YOUR SPEAKER
Connect both ends of your speaker coil to your amplified audio signal. If you can not hear your speaker, try holding it very close to your ear. If it is very quiet then it is working, but you might need to increase your power source or reconsider your coil design to make it more efficient at moving air, which is what makes it louder.
Some simple ways for amplifying various audio signals >> http://www.kobakant.at/DIY/?p=3794
Another version of the speaker playing: