Invention of the telephone
The carbon microphone was independently developed around 1878 by David Edward Hughes in England and Emile Berliner and Thomas Edison in the US. Although Edison was awarded the first patent in mid-1877, Hughes had demonstrated his working device in front of many witnesses some years earlier, and most historians credit him with its invention.
Peter L. Jensen
He built with Edwin S. Pridham the first moving coil loudspeaker in 1915. Called the moving coil principle, the electro-dynamic principle from which the term dynamic speaker later evolved. In 1916 he built and patented the first contained and complete electric reproducing phonograph. Made the first public address system and used on Christmas Eve in 1915 in San Francisco at a gathering where 75,000 people were present and who heard distinctly all the speeches and announcements. The public address systems under the name of Magnavox were used all over the United States. It was used by U.S. President Woodrow Wilson in 1919. World-wide there were no other companies manufacturing public address systems until 1920. He designed the Magnavox dynamic loudspeaker for reception of radio broadcasting in 1919.