Inventors who worked on the acoustic telegraph included Charles Bourseul, Thomas Edison, Elisha Gray, and Alexander Graham Bell.
Their efforts to develop acoustic telegraphy, in order to reduce the cost of telegraph service, led to the invention of the telephone.
Acoustic telegraphy was similar in concept to present-day FDMA, or frequency-division multiple access, used with radio frequencies.
Acoustic telegraphy devices were electromechanical and made musical or buzzing or humming sound waves in air for a few feet.
But the primary function of these devices was not to generate sound waves, but rather to generate alternating electrical currents at selected audio frequencies in wires which transmitted telegraphic messages electrically over long distances.