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.
History of hearing aids
The first electric hearing aid, called the Akouphone, was created by Miller Reese Hutchison in 1898. It used a carbon transmitter, so that the hearing aid could be portable. The carbon transmitter was used to amplify sound by taking a weak signal and using electric current to make it a strong signal. These electronic hearing aids could eventually be shrunk into purses and other accessories.