Austenite Conditioning Research Articles

Magnetic Recording of Sound

A LECTURE on “Developments in Magnetic Recording” was given by Mr. P. T. Hobson to the British Sound Recording Association on March 27, with demonstrations of the wire-recording machine now in production and available in small quantities for non-entertainment purposes. A model of a high-grade instrument shows that the technique of wire-recording has risen so rapidly in recent years that the quality of reproduction obtained can be classed as high, if not higher, than with the best disks and the Philips-Miller system. The comparative cheapness of the wire, the possibility of erasure and the immediate rewind makes magnetic recording attractive for many purposes, apart from the straight and protracted reproduction of music. Ever since Poulsen discovered the possibility of magnetic recording nearly fifty years ago, designers have been misled by the erroneous idea of the exact process of magnetization. Research by the Armour Corporation of the United States and also in Britain has led to the selection and heat-treatment of the steel wire so that a diameter of only 4 mils and a velocity of 24 in. a. second can give high-quality reproduction with a, signal-to-noise ratio of some 60 decibels. The material is a stainless steel, heat-treated with a current to bring it into the austenitic condition, and with a maximum ratio of the coercive force to remanence, this being the condition for minimizing the almost complete self-demagnetization of the disk-like magnets of which the wire seems to be comprised at the highest frequencies and shortest wave-lengths with tolerable loss.