In 1924, Robert Mathes of Bell Telephone Laboratories filed a broad patent covering essentially all electromechanical delay lines, but focusing on acoustic delay lines where an air column confined to a pipe served as the mechanical medium, and a telephone receiver at one end and a telephone transmitter at the other end served as the electromechanical transducers.
In 1924, Robert Mathes of Bell Telephone Laboratories filed a patent for all types of electromechanical delay lines, with a focus on acoustic delay lines where an air column within a pipe acted as the mechanical element, and a telephone receiver at one end and a telephone transmitter at the other served as the transducers.