Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS
Rough Science
Explore the Challenges
Solve the Web Challenge
Meet the Rough Scientists
About the TV Series
Discover More
Site Map
Explore the Challenges

The Challenge: Record a Sound or Voice

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

Thomas Edison's Phonograph