Fig. 323 – The Young’s machine, capable to reproduce the sound vibrations in a chart.

Since the beginning, mankind wanted to record and playback the natural sounds. Shelled hands were used to amplify battle cry by the ancient tribes. In the middle ages several musical instruments were already known. Therefore it was not possible to record the sound waves.
Fig. 324 - The phonautograph invented by Martinville.
In the XVIII century through the birth of new studies several branches of the natural and physical sciences were improved deeply. Thus, for instances: Acoustics with Gay-Lussac studies; Arago calculating the velocity of sound in the air; Savart determining musical pitch by mean of a toothed wheel and, Helmholtz bringing into practice the harmonics’ law.
Certainly, those scientific improvements were the basis for the delineation of the principles to be used either for recording as well as the reproduction of the natural sound.
Thomas Young was the first to reproduce the sound vibration through a chart. Fig 323
In 1817, Leon Scott de Martinville invented “the phonautograph”, basically consisted of a trumpt that collected the air vibration actuatying as a resonant chamber. Fig. 324
Fig. 325 - Edison and his invention the phonograph.
At the smaller end of trumpt there was a thin membrane, which convert the alternate air pressures into mechanical movements; later this kind of device was named as diaphagram.
In April 1877, Charles Cros introduced to the French Science Academy a project for a sound-reproducing machine.
Therefore, Thomas Alva Edison invented the practical conception for a machine capable to record and reproduce the natural sounds accidentally in 1870. In the reality, Edison was in the course of a series of extended experiments to improve the telegraphic transmissions, which firstly encode a message by mean of holes made in a strip of paper, from which at any subsequent time might be automatically sent.
Basically this machine consisted a disc in which was wrapped a piece of paper.
The message was recorded by indentation made by mean of a needle during the rotation of the disc. In manipulating the strip of paper Edison found that that when the indented paper was turned with great swiftness, it gave of a humming sound resembling that of the human talk heard indistinctly.
Fig 325A - The original Edison’s phonograph project.
This led him to think if it were possible to use the oscillation of the needle to record the human speech.
As yet the Edison’s machine to record the human speech was crude, but is characterized by wonderful mechanical precision.
The machine that Edison designed consisted basically of a metall

cylinder, which was mounted on a screw; so that turning a handle would make it both revolve and move from left to right.
Over the cylinder provided with final spiral grooves impressed in its surface. On each end of the machine were assembled two diafragm-and needle units in such away one to be used for recording, and the other for reproduction of the sounds.
A piece of tin foil was wrapped around the cylinder, and thereon the recording needle, following the spiral grooves, would indent a pattern of the sound vibration directed into the mouth piece. On replaying, the reproduction needle was to convert these indentions on the tin foil back into sound.
Since February 29 1877, when a patent was granted, this machine as known as phonograph, has arisen enormous curiosity and just one year a after his launching circa 600 units was already built and in this way carving out the way for the phonograph industry. Fig. 325

Fig. 325B - An early office’s recorder made in 1920 by the American company Dictaphone Corporation using the same principle of the Edison’s phonograph. Fig. 325C - A detailed overview of the office’s recorder.