[This note covers all of the notebooks in Group 7: Phonograph Experiments -- Recording and Reproducing Apparatus.]

This subgroup contains three notebooks regarding the phonograph machine itself and includes material on the improvement of recording and reproducing mechanisms. The first book contains two pages of notes by Frederick P. Ott on diaphragms. The second book covers the period 1905-1910 and was used by Charles N. Wurth, a long-time Edison employee, to describe his work on phonograph recorders, reproducers, and attachments, as well as the composition of records and the duplication of masters for record manufacture. Also included are a few experiments on a combined phonograph and motion picture device. The third book is from the Legal Department Records and pertains to the patent interference case, Dennison v. Pierman (no. 28,395). It contains Alexander N. Pierman's notes on a pneumatic amplifier, a device that is also mentioned in Wurth's notes.