Preliminary Report on a High Fidelity Reproducer for Lateral Cut Disk Records
Frederick Vinton Hunt, J. A. Pierce · The Journal of the Acoustical Society of America · 1938
The moving element of the reproducer is a horizontal, single-turn, elongated loop of phosphor bronze ribbon which is driven by an inverted conical shell whose base is attached to the free end of the loop and whose apex bears a sapphire stylus. In the front half of the loop, which passes through a concentrated magnetic field, the ribbon lies in the vertical plane and is bent into a channel to increase its rigidity. In the remainder of the loop the ribbon is twisted into the horizontal plane and its ends are clamped between insulating blocks. This provides a light structure which is relatively stiff for lateral displacement but quite flexible in torsion, so that a lateral vibration of the stylus is converted into an oscillation of the stiffened portion of the loop about its longitudinal axis. Damping is provided by a membrane of Pyralin connecting the free end of the loop with the adjacent magnetic structure. The mass of the entire moving system is approximately 50 milligrams and the unbalanced weight on the stylus is less than six grams. The electrical output is approximately 50 db below that of a standard transcription reproducer, but the response is proportional to the recorded velocity amplitude within ±3 db from 30 to 18,000 cycles.