Magnetic plate telegraphone with user

Peder Oluf Pedersen, a close associate of Valdemar Poulsen, developed the idea of a rotating steel plate for voice recording instead of steel wire in 1901. The device was improved further at the American Telegraphone Co., whereby a large steel plate was added, giving it a recording capacity of 4 minutes. However, the magnetic disk recorder was virtually unsaleable: it cost $300 while a phonograph with the same playing time and a louder volume was available for only $70.