Invention of the speaker

I just read this autobiography by Peter L. Jensen (1886), called "Jensen, højttalerens opfinder" (1948). The history about the invention of the speaker varies depending on the source The earliest small speakers used in telephones was invented in 1860-1880, but the use of speakers to amplify the voice so that a speech could be heard by thousands at the same time, seems to be realised by Jensen in 1915. The speaker was based on the moving coil principle, which was already known, so he didn't get a patent. Some guys from AT&T got it almost 10 years later due to some improvements and more specific descriptions.

The book describes Jensen's work with Valdemar Poulsen on the first radio transmissions and the race against the spark transmitter of Marconi. And how he moves to U.S.A. in 1909 and experiences really loud feedback for the first time when testing the loudspeaker prototype. There are also stories about the invention of the electrical turntable cartridge and the radio tube. So the book is both a 1st person story about the early days of electrified media and a really interesting adventure of the son of a fisherman who became an important inventor. I borrowed it from this guy who got it from his father.