Who invented headphones?

The first headphones were invented by American engineer Nathaniel Baldwin in 1910. His invention was the end result of experimentation with the principle of sound amplification by compressed air. Baldwin patented and then sold his invention to the U.S. Navy.

The sensitivity of Baldwin's headset, tested by engineers of the Radio Division of the Navy, was twice that of others on the market at the time. His manufacturing output of the devices was limited, however, as he hand-built every headphone set the Navy ordered at his kitchen table. They were superior in quality to alternatives at the time, so the Navy accepted his limited output.