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Stereophonic Record and Elliptical Stylus

   Last Modified:    Published: 2021/05

Elliptical stylus picks up the stereophonic sound. Enjoy the world of Hi-Fi recording...

Stereophonic Record

Audio Fidelity first stereo LP
Audio Fidelity –, Public domain, link

An innovative LP record makes a great stride again. That was stereophonic recording for LP records.
LP records providing good sound quality spread rapidly, “Hi-Fi” had became vogue-word. Just at that time, there happened a big event in the record industry. The tape-recorder gained in popularity.
Since then tape recorder made a great progress by increasing number of channels. Stereophonic record enabled sound reproducing by using multichannel recordable tape as master source, became more active area of research. Beginning of stereophonic recording was Cook’s binaural record. It was a kind of eccentric method that tracing 2 grooves for inside and outside respectively using 2 cartridges which was connected to one tone-arm. Because binaural recordings have 2 separate monophonic bands (inner and outer) the cartridges needed to start playing each channel at the same time. Since then various method was studied over to it to practical use but 45/45 type of Westrex was adopted by recording companies and kept using it till today.
Stylus also advanced as well as a stereophonic record which has complex amplitudes on a groove quite extensively.

Appearance of Elliptical Stylus

With the appearance of elliptical stylus, its profile is that whilst the broader radius across the width of the groove determines the height at which the stylus rides in the groove, the smaller radius of that part of the stylus in contact with the wall of the groove enables more accurate
tracking of the high frequency modulations of the groove. 45/45 method is that sound of 2 channels on both left and right is to cut a record onto the groove’s side wall 45°slanted. However, the groove changes from place to place as shown.
The depth of groove also changes as the frequency changes. In order to trace the grove for stereophonic sound, stylus itself has to have a higher traceability. The spherical stylus can no longer take the task because there is a limit in forming smaller radius, caused tracing distortion. It had a difficult time following wide side to side motions of the groove with high frequencies. The groove narrows at transitions and tends to pinch at the stylus. This is a cause of distortion.

The elliptical stylus was devised to solve these shortcomings. The radius has 0.2 ~ 0.3 mil so close to the spec of cutting stylus. It is good to follow the groove narrowly. Also, tracing distortion towards horizontal direction and a pinch effect for vertical direction were drastically improved.

The explanation of the record needle is also available on this page.
Stylus Tip

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