Carbon microphone
The first microphone that enabled proper voice telephony was the (loose-contact) carbon microphone (then called transmitter). This 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.
David Edward Hughes
In 1878 Hughes published his work on the effects of sound on the powered electronic sound pickups, called "transmitters", being developed for telephones. He showed that the change in resistance in carbon telephone transmitters was a result of the interaction between carbon parts instead of the commonly held theory that it was from the compression of the carbon itself. Based on its ability to pick up extremely weak sounds, Hughes referred to it as a ""microphone" effect" (using a word coined by Charles Wheatstone in 1827 for a mechanical sound amplifier). He conducted a simple demonstration of this principle of loose contact by laying an iron nail across two other nails connected to a battery and galvanometer. His paper was read before the Royal Society of London by Thomas Henry Huxley on May 8, 1878 and his new "microphone" was covered in the July 1 edition of "Telegraph Journal and Electrical Review". Hughes published his work during the time that Thomas Edison was working on a carbon telephone transmitter and Emile Berliner was working on a loose-contact transmitter. Both Hughes and Edison may have based their work on Philipp Reis' telephone work. Hughes would refine his microphone design using a series of "carbon pencils" stuck into blocks of carbon to better pick up sound but never patented his work, thinking it should be publicly available for development by others.