The Challenge: Record a Sound or Voice
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Given the limited materials available to us, we decided to make a recording on a phonograph.
How does a phonograph work?
Sound is collected
by a horn
that is attached to a diaphragm.
The sound causes vibrations in the air that travel down the horn causing
the diaphragm to vibrate. The diaphragm is connected to a stylus
and pressed into a cylinder covered in wax (or alternatively a thin layer
of tin foil). When a handle is turned, the cylinder rotates and also moves
very slowly along. The stylus pushes into
the wax and, when the cylinder is rotated, cuts a groove.
The stylus also moves up and down very slightly as it vibrates with the
sound and so the wax now contains a recording
of the sound in the groove.
We play the sound back by using the stylus to translate the groove back
into vibrations onto the diaphragm and this in turn to the horn from which
the sound can be heard. Although the phonograph idea is simple enough
it was a triumph of engineering. The movement of the cylinder and groove
need to be very accurately aligned in order for the machine to work at
all. This is a difficult thing to do and requires precision engineering!
Thomas Edison's Phonograph
The Rough Science Phonograph