Use a broken speaker, bits of wire, and
tape to prepare a coneless voice coil
driver, then use it to generate standing
waves on a sheet of metal, making
sound visible. Magic!
My knowledgeable friend Robin once said that you don’t
need to worry about having too big an audio amplifier,
because speakers are usually damaged by under-powered
amps working too hard and clipping the signal, creating
rough square waves with too much power. I learned that
this is true when I melted a speaker’s coil by running a
strong 20Hz signal through it, to drive a vortex cannon
(MAKE, Volume 15, page 114).
On the bright side, I now had a nice speaker magnet to
use as the foundation for something else I wanted to try,
a Chladni plate!
Early acoustics researchers Robert Hooke and Ernst
Chladni (CLOD-knee) found that fine powders sprinkled
on a vibrating plate would settle in patterns that showed
how the plate was vibrating. They got their glass and
metal plates vibrating for their experiments by running
a violin bow across the edges. In our updated version, we’ll
generate the vibrations using a voice coil driver, which is
basically a speaker without the cone.
Photograph by Ed Troxell
Set up: p. 125
Make it: p. 126 Use it: p. 131
Edwin Wise is a software engineer with 25 years’ experience. He develops software during the day and explores the
edges of mad science at night. He can be found at