The compact disc has taken away the phonograph record for most people. Here are a few comments about the properties of this still quite viable recording system:

  1. How many grooves are on the average LP record? Over a thousand? Nope! There are only two: One on each side. The groove spirals in from the edge to the center.
  2. On the subject of sides, how many ways of sequencing record sides have been used for multi-disc albums? The answer is four:
  3. On the subject of record changers, several methods have been used to detect the end of a record:
  4. How is sound recorded on a record? The groove wiggles back and forth in the surface of the record. These wiggles correspond to the waveform of the recorded sound. As the playback stylus follows these wiggles, it vibrates with them, producing the audio signal.
  5. How does the record changer separate one record from the stack to drop it? There are two methods: Some record changers required that a plastic insert (a spider) be put in the large hole to make the record fit the standard .25" spindle.
  6. Why are there four speeds?
  7. Why did RCA make the spindle hole larger in the 45 rpm record? They did it to make a record changer with all of the record-dropping parts in the spindle. No reliable way of doing it with the .25" hole had been made at the time, so RCA used a 1.5" hole. It was also a ploy, so that you had to buy their player to play their records. But just before the 45 was released, the .25" center push spindle was perfected, and the problem was solved (but the large hole remained). Also, Farnsworth produced a working umbrella spindle which needs no side shelf or overarm just before the 45 was introduced.
  8. Why are there three sizes of records?
  9. How do record changers handle the different sizes?

    See my page on the subject.

  10. How do record changers know when to shut themselves off?
  11. How does the compact disc measure up to the LP?