18 Nicolas Collinsuse a jumper lead to make a connection between the bare wire and terminal.
Connect the free end of the other battery wire to a plate or chunk of some
conductive metal: a pie tin, scrap copper flashing, an anvil, a piece of girder, a
brake drum, a frying pan, a file, etc. -- the rougher the metal surface the better.
You’ll probably have to make this connection with a clip or clamp. Clip one end
of a jumper lead to the other terminal of the speaker and the other end to a nail.
Tap the nail on the plate. When it touches the metal the nail completes the circuit
and sends 1.5 volts to the speaker coil, making the cone jump. By scraping the
nail across the metal you can produce pleasing, if scratchy, percussive sounds.
You can use your hands, bowls or toilet plungers to mute and resonate the sound
further. Put gravel, loose change or dried lentils inside the cone for additional
rhythmic accents.
Avoid holding the nail on the metal for an extended period of time –
loudspeakers get hot and bothered when presented with a steady DC voltage, so
it’s better to send them shorter pulses.
Instead of nails on the plate, you can clip the leads to two paperclips, washers, or
loops of copper wire that you place inside the speaker cone. The cone jumps
when contact is made, breaking the contact for a moment, then the metal bits fall
against each other and the process starts all over – a mechanical oscillator.
You can put more batteries in series if you want a louder sound, but at some
point you may blow out the speaker with excessive voltage, so be warned: don’t
try this with your roommate’s Bang & Olufsen, and don’t plug a speaker directly
into the wall. A 9 volt battery has a small current capacity, so will go flat pretty
fast if used in this circuit -- stacked “C” or “D” cells will last longer.