Magnetic Format
Poulsen's original telegraphone and indeed all very early recorders placed the two poles of the record/replay head on opposite sides of the wire. The wire was thus magnetised transversely to the direction of travel. This method of magnetization was quickly found to have the limitation that as the wire twisted during playback, there were times when the magnetization of the wire was at right angles to the position of the two poles of the head and the output from the head fell to almost zero.
The development was to place the two poles on the same side of the wire so that the wire was magnetised along its length or longitudinally. Additionally, the poles were shaped into a "V" so that the head wrapped around the wire to some extent. This increased the magnetising effect and also increased the sensitivity of the head on replay because it "collected" more of the magnetic flux from the wire. This system was not entirely immune to twisting but the effects were far less marked.
The longitudinal method survives into magnetic tape recording to this day.
Read more about this topic: Wire Recording
Famous quotes containing the word magnetic:
“We are in great haste to construct a magnetic telegraph from Maine to Texas; but Maine and Texas, it may be, have nothing important to communicate.”
—Henry David Thoreau (1817–1862)