Four-Channel Phonograph Bi-Radial Point Playback Criteria
For accurate and wear free record player for CD-4 (discrete 4-channel) reproduction, true Bi-Radial point dimensions must be accurately maintained, such that the long radium shall be 3x10-3 inches and the short radium shall be 2x10-4 inches. Tracking, tracing, record bearing load and apparent record bearing surface stiffness establish those values critically. Scanning Electron microscope photos show actual radii of points in use. Frequency response curves show the need to maintain these radii to give acceptable performance at the innermost groove.
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