Modern earphones were designed by Nathaniel Baldwin, who submitted his ideas to the Navy for testing in 1910. However, there were many designs of in-ear pieces that predated Baldwin's and contributed to his ideas.
Stethoscopes were one of the earliest in-ear devices. In the 1850s, they were invented for listening to a patient's heart and lungs, and Thomas Edison used them with his phonograph machine. In the 1890s, British opera houses and theaters started supplying the audience with rudimentary headphones. In 1891, Ernest Mercadier invented the bi-telephone, a pair of earbuds that blocked out noise.
With the Navy's guidance, Baldwin's final design consisted of two sound receivers, each containing a mile of copper wiring, attached to the operator's headband. This design was the foundation for electricity-free telephones used in World War II.
John Koss then developed the first commercialized stereo headphones in 1958. In 1979, Sony invented the Walkman.