Gerald Fabris, Curator of the Edison Historical Site in West Orange, NJ, gave a demonstration of wax cylinder recording and playback at the Boston Public Library on Tuesday. It was a fascinating presentation. It turns out the phonograph was preceded by a device called a phonautograph. This worked similarly to a traditional seismograph: a moving stylus draws a waveform on a long, scrolling sheet of paper. In this case, the stylus is attached to a diaphragm which vibrates with the compression and rarefaction of the air. So the stylus is drawing sound waves. The inventor of the phonautograph, Édouard-Léon Scott de Martinville, had no way to play back his recordings, but quite recently the documents were scanned into computers and turned back into sounds for the first time. The sounds were played during the presentation. It was very muddled, but it definitely sounds like a human voice!
Thomas Edison‘s phonograph worked the same way, with a diaphragm vibrating with the sound waves, but instead of drawing back and forth on paper the stylus pushed in and out against a rapidly spinning, slowly advancing, tinfoil covered cylinder. In this way, the stylus digs a helical grove into the tinfoil with varying depth. The pattern of changing depth, of course, encodes the sound wave. The process is reversed for playback. A more blunt “needle” presses against the groove as the cylinder spins. The needle, in turn, pushes a diaphragm. As the needle is pushed in and out by the varying depth of the groove, so is the diaphragm – and the recorded sound is reproduced.
Through the years the material of the recording surface and many other details of implementation were altered and refined. I’m not going to attempt to replicate any particular historical phonograph. I’ll pick what I see as the most practical way to prove the concept. I’ve found several guides on the internet for how to build a simple phonograph. I’m going to see how well this one works for me: http://www.creative-science.org.uk/RS2phono.html.
I’ll try to interleave my work on this with the throwing spear discussion. For the paleolithic era, I plan to make my throwing spear, finish watching Becoming Human, and possibly visit a museum or two. Then I’ll move on until the weather gets warmer. Then I’ll go back and finish some of the outdoor paleolithic activities such as fire-making and shelters.
Thank you for reading!
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