Vox wire recording device, the "Silent telegrapher"

This wire recorder was developed in 1922 by Waldemar Hagemann at Kurt Stille’s Vox Maschinen AG. The large wire spools were new, because the steel wire had to pass through the magnets at 6.5 feet per second (3 m/s) to achieve good sound reproduction. Therefore, 30 minutes of recording time required 17,700 feet of wire (5.4 km) which weighed 4.4 pounds (2 kg). Commercial success was poor. Notable people who used this device were the author and screenwriter Thea von Harbou (the wife of Fritz Lang), and the novelist Hans Dominik.