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waves encoded on the record. The needle was attached to a diaphragm and a horn As the development of the phonograph continued, sound was recorded on card- board cylinders coated with wax. During the last decade of the nineteenth century and There are a number of problems with phonograph records. As the needle follows along the groove of the rotating phonograph record, the needle is pushed back and Another problem occurs at high frequencies. The wavelength of the sound on the record is so small that natural bumps and graininess in the plastic create signals as loud S E C T I O N 17. 5 • Digital Sound Recording 529 Figure 17.12 An Edison phonograph. Sound infor- mation is recorded in a groove on a rotating cylinder of wax. A needle follows the groove and vibrates accord- ing to the sound informa- tion. A diaphragm and a horn make the sound in- tense enough to hear. Example 17.7 Wavelengths on a Phonograph Record Consider a 10 000-Hz sound recorded on a phonograph rev/min. How far apart are the crests of the wave for this sound on the record (A) at the outer edge of the record, 6.0 inches from the center? 33 1 3 (B) at the inner edge, 1.0 inch from the center? Solution (A) The linear speed v of a point at the outer edge of the record is 2,r/T where T is the period of the rotation and r © Bettmann/CORBIS |