What about speeds?

The first disc records were cut at various speeds centering around 78 RPM. Since the recording and playback turntables were spring wound with mechanical governors to regulate the speed, the only real way to determine the correct playback speed was to have perfect pitch, and know the music. Once electrical motors became the standard, the recording speed had to become standardized. The 4 pole motor turns at 1800 RPM, therefore a gear ratio of 1:23 gives 78.26 RPM. This became the standard for most disk records.

In about 1926, Western Electric started to experiment with synchronized sound on disk for films. There had to be some standardization.

First, what speed should the film run? Each reel of a silent film had instructions for the projectionist for how many feet per minute the reel should run, on average, 90 feet per minute. Some movie houses would just crank them at top speed to get people in and out. 90 feet per minute, or 24 frames per second became the standard. This required gearing of 1:1.25 to run the intermittent sprocket drive which advances the film through the gate at 1440 RPM.

At 90 feet per minute, a 1000 foot reel of film will last 11 minutes. Western Electric and Warner Brothers went to the Brunswick Phonograph company to see what would be the largest record that could be pressed for mass production. 16 inches was the answer. To fit 11 minutes on this larger size, a new slower speed was needed. This worked out to 35 RPM. This would be a 1:51.43 ratio from an 1800 RPM motor. 33-1/3 worked out nicely with a 1:54 ratio, so that’s what was agreed upon.

According to strict laboratory procedures, we should have made exhaustive tests and calculations and six months later come up with the correct answer. What happened was that we got together with Warner’s chief projectionist and asked him how fast they ran the {silent} film in theaters. He told us it went at eighty to ninety feet per minute in the best first-run houses, and in small ones anything from one hundred feet up, according to how many shows they wanted to get in during a day. After a little thought, we settled on ninety feet a minute as a reasonable compromise. We had our disks processed by the commercial record companies, and the largest diameter they could handle was about seventeen inches. With a record of that size, the optimum speed to get the ten minutes of recording time we needed was somewhere around 35 revolutions a minute. We standardized at 33-1/3, because that happened to fit the best with the gearing arrangement our engineers were working out for coupling the turntable to the picture machine.

Western Electric Engineer Stanley Watkins (1961) Scott Eyman THE SPEED OF SOUND: Hollywood and the Talkie Revolution 1926-1930. p. 112.

33-1/3 was used for early sound film into the early 1930s where sound on film finally became the standard. The 16” 33-1/3 record continued to be used for radio transcription, and for syndicated radio shows. The 33-1/3 twelve inch LP was introduced for consumers by Columbia in 1948.

RCA developed the 7” 45 in 1949. They also used the larger 1-1/2 center hole to make it easier for DJs to handle the record. So why 45?

The clarity of a 7" record turning at 33-1/3 isn't very good even with the new microgroove stylus. How did they arrive at 45? This is my theory. RCA had a number of transcription turntables that ran 78 and 33-1/3. The drive motors were geared 1:23 from 1800 RPM to 78.26 RPM. Just under the platter was a planetary ball bearing. The inner race rotated at 78.26 RPM. The five balls were in a keeper that drove the platter. When the outer race was locked to the platter, the balls and outer race were locked making the whole bearing turned at 78 RPM. When the outer race was locked stationary, the balls and hence the platter turned at 33-1/3 RPM. The RCA 70-C and 70-D series were in large production, and used in most radio stations. This bearing was very unusual as the inner race was machined to 1-79/128”, the outer race to 2-23/128” and used standard 9/16” balls. Not exactly an off the shelf size. Since planetary gearing works on subtraction, if you were to rotate the outer race at 78, and hold the inner race stationary, the balls would turn at 45 RPM, well actually 44.92753623 RPM. Close enough. This also allowed the standard 1800 RPM motor geared at 1:40 to produce 45 RPM. With the smaller microgroove stylus’s, the groove velocity with the smaller diameter at 45 RPM still could be as clear as the larger standard stylus’s at 78 RPM.

16-2/3 RPM and 8-1/3 RPM are just halving of the 33-1/3 RPM. These were used for Talking Books for the blind. Since these were voice only, running the tape at double or quadruple speed accomplished the half 16-2/3 or quarter 8-1/3 speeds for playback. 16-2/3 was also used for Seeburg Basic Music Library, a competitor to Muzak in stores, and the Highway Hi Fi car record player.