Abstract: An optical data recording disc has a protrusion forming layer which is formed on a gas generating metal layer, and the gas generating metal layer, in turn, is formed on an optically polished disc. An optical beam is modulated by data and impinges on the gas generating metal layer, which locally evaporates the metal layer to form a gas. The gas expands and produces protrusions in the protrusion forming layer, and these protrusions are representative of the data. Accordingly, because the protrusions are formed essentially simultaneously with the recording operation, it is possible to reproduce the data being recorded immediately after the data is recorded so that failures in a recording device or in the optical data recording disc can be detected immediately.

Abstract: A diaphragm for use in a loud speaker is constructed of a substrate formed into a diaphragm configuration from a thin plate or a sheet composed of an organic or an inorganic substance, and a coating layer made of boron, or, an alloy of which a major component is boron or a chemical compound of boron, being provided onto at least the surface of said substrate.