The history of electronic music is probably longer than many of us think. After all Thomas Edison invented the phonograph or gramophone around 1877.
"Talking Machines", V. K. Chew, 1967, SBN 11290162X
""From Tin Foil to Stero", Oliver Read and Walter L. Welch, 1959
"Electric Sound: The Past and Promise of the Future of Electronic Music", Joel Chabede, (Paperback 1996)
"The Computer Music Journal", volume 33, number 3, Fall 2009, MIT Press, ISSN 0148-9267
All but one article in the above journal are devoted to Max Mathews, the "founder of computer music".
"The Technology of Computer Music", Max V. Mathews,1969,Cambridge, Massachusetts, MIT Press
"Electronic and Experimental Music", Thom Holmes, 2008, ISBN 978-0-415-95782-3
The following website cotains a 42 page article which is about important events in the history of electronic music. It is by David Dunn and can be downloaded.
The following two links give timelines to the important developments in the history of electronic music: