The Edison Disc, also known as a Diamond Disc record, was a type of audio disc record marketed by Edison Records from 1912 to 1929. They were known as Diamond Discs because the reproducer fitted to the matching Edison disc player was fitted with a diamond stylus.
80 RPM 'Diamond Disc' records. Note the thickness of each record.

Edison had previously concentrated on producing phonograph cylinders but decided to get into the disc market due to the increasing market share of disc sound recordings, especially the discs of companies such as Victor Talking Machine Company (the format of which would evolve into "78 records"). Victor and most other disc record companies used side to side or lateral motion of the stylus in the record groove, whereas in the Edison system the movement was up and down or vertical (also known as "hill-and-dale" motion), as in a cylinder record. An Edison Disc Phonograph is distinguished by the diaphragm of the reproducer being located parallel to the disc surface. The Victor (or similar) diaphragm is located at a right angles to the surface of the disc such that the diaphragm is more or less parallel to the groove.

The grooves on an Edison Disc are smooth on the sides and have a variable depth. Standard lateral discs will have a more constant depth, but the sides of the groove are scalloped. As the Edison groove pitch (or "TPI", i.e. "threads per inch") was 150, a much finer grooving than that on lateral discs, Edison's 10-inch discs played considerably longer than Victor's or Columbia's -- up to nearly five minutes per side. The Edison Disc is also ¼-inch thick (supposedly to prevent warping), and was filled with wood flour, and later, china clay.[1]

Victor's system could not play Edison Discs as the needles used would cut through the recorded sound, and the Edison system could not play Victor or other lateral discs unless one used special equipment, like the Kent adapter. There is an example of a device to play Edison discs on a Victor machine.[2] The Brunswick Ultona and the Sonora Phonograph were the only machines besides the Diamond Disc player that could play Diamond Discs, but Edison made an attempt at curbing this (a phonograph/gramophone that could play Edison, Victor/lateral 78s, and Pathé discs) by stating "This Re-Creation should not be played on any instrument except the Edison Diamond Disc Phonograph and with the Edison Diamond Disc Reproducer, and we decline responsibility for any damage that may occur to it if this warning is ignored.

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