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 encompassing all electromechanical delay lines broadly, but specifically focusing on acoustic delay lines where an air column confined to a pipe acted as the mechanical medium, and a telephone receiver at one end and a telephone transmitter at the other served as the electromechanical transducers.