Fig. A: Coil paper strips lengthwise around the magnet,
taping each one closed (but not to each other). Then
remove the magnet. Fig. B: Wind 50 turns of wire around
the paper coil and secure with tape.
Fig. C: Put the magnet in the cylinder and glue the
magnet to the cardboard base and the folded business
cards to the plate. Fig. D: Cut and strip the wires from
the audio plug and connect them to the coil.
3. Put the magnet back inside the cylinders, and then
wind the wire around them, about 50 turns. The coil
should have more than 7 ohms of impedance. Leave
some extra wire length at each end, and after you
finish winding, secure the coil with tape (Figure B).
4. Remove the magnet and then remove the inner
cylinder. It’s OK to tear it, but try not to damage the
5. Accordion-fold the 2 business cards widthwise
into W shapes. Then glue 1 end of each to the back
of the plate, so the cards are parallel and stick up
symmetrically on either side of the cylinder.
6. Replace the magnet in the cylinder. Put some glue
on the free ends of each business card, and a little bit
on the magnet, but not enough to squeeze away and
touch the inside of the cylinder. Position your piece
of cardboard or wood on top, with the plate centered
underneath — this will be the speaker’s base. Flip
everything over so the base is on the bottom and the
plate faces up. The magnet should fall down and glue
itself onto the base, with the business cards glued
symmetrically on either side. The cylinder should
hover around the top of the magnet (Figure C).
132 Make: Volume 12
7. Make sure that the coil wires are separated and
aren’t touching anything. Cut and strip the wires from
the audio plug and connect them to the coil (Figure D).
Allow glue to dry.
Your homemade speaker is ready! I plugged mine
into my computer. The volume was good, and the
sound quality was really good. I can listen to music
across the room.
Make sure the business cards are parallel, and try
gluing them closer to or farther away from the coil,
until you find the distance that produces the most
and best sound.
If your speaker sounds horrible, check that the
coil is tight and secure, with nothing loose, and
that all other wires move freely, without anything
touching them. Make sure the business cards are
completely glued and that they’re the only things
that touch the foam plate. The coil should not touch
the magnet or the base of the speaker. If it does,
make the coil wider or don’t fold the cards as tightly.
Photography by José Pino
José Pino is an inventor who lives in México and likes electronics.
See his projects, crazy ideas, and more at josepino.com.