The Edison gramophone amplifies sound via a loading chamber

Evidence

Figure 7.6 (Left) A chamber housing a piston has a relatively small diameter exit, such that the chamber pressure varies considerably as the piston moves in and out. Energy must be expended to overcome the pressure differences, which always oppose the movement of the piston. This energy will ultimately be imparted to the air, and if the frequency of the piston is high enough, audible sound will be produced. (Right) From a Thomas Edison patent application, an Edison gramophone, ca. 1888. The gramophone works in a similar way, with the role of the piston played by a flexible membrane actuated by a thread from a diamond needle. The needle oscillates as it rides in the grooves of a recorded cylinder. The track undulates perpendicular to the cylinder, causing the needle to pull on the membrane according to the groove depth. The chamber to the right of the membrane loads the source, which here is the vibrating membrane. — Eric J. Heller, Why You Hear What You Hear- An…, 537

Categorization

• XREF: Concrete applied example of the piston-loading mechanism bridging the physics model to a real device — usable example when explaining why we hear what we hear.
• CANDY: The gramophone’s tiny membrane-loaded-by-chamber amplification trick is a fun fact about how early recorded audio worked.