In This Section
- First Book in "AES Presents" Series from Focal Press
- New edition of Handbook for Sound Engineers, edited by Glen Ballou
- 137th Audio Engineering Society Convention Breaks Records and Draws Acclaim from Attendees, Exhibitors and Presenters Alike
- Convention reminds West-Coast audio community, “If It’s About Audio, It’s At AES!”
- AES 2014 Election Results
- The results are in!
- Time to Vote: 2014 AES Elections
- Deadline was Friday, July 11th
Record SpeedsThe 78 rpm record speed was standardized by Victor for its spring motor phonograph in 1901. The 33-1/3 speed was created by J. P. Maxfield for the electrical recording system developed at Bell Labs in the early 1920s. The 45 rpm speed was created by RCA Victor for the 7-inch microgroove record in 1949.
The following selection is from "Before the Fine Groove and Stereo Record and Other Innovations ....." by Warren Rex Isom, Journal of the Audio Engineering Society, October/November 1977, Vol. 25, Number 10/11:
". . . One of the most important innovations in the record industry was the change of record speeds, in spite of the fact that generally speaking it matters little what the speed is; it is only important that it be the same and constant.
Back in the handcranked phonograph days when the same instrument was used for both recording and reproduction, what was recorded had to be reproduced at close to the same speed, otherwise, the difference between recorded and reproduced material would have been too great. However, within broad limits, the exact speed was unimportant. Several factors determined what the broad limits were. For better quality, the crank was turned at a comfortable speed, otherwise jerky motion resulted. This comfortable speed as found to be about heart-beat rate -- between 60 and 90 per minute. It is interesting to note that armies and bands match at this cadence. and speeds in this range are specified for handcranked farm equipment.
Those who used handcranked phonographs soon learned that if they turned at a lower speed more time could be recorded on the record. but lower speeds gave bad sound. At higher speeds. the sound was better but the recording shorter. They also knew that larger records played longer than smaller records. The original cylinder records were large in diameter and almost impractical in size. Spring-wound motors were necessary before the cylinders could be reduced in size and operated at speeds first of 120 r/min and, later, at 160 r/min for good sound. These speeds were beyond the comfortable range for manual operation. It was soon found that speed is one of the variables of a record system specification. The other variables are the quality objectives, the quality of the recording materials, the size of the record, the length of play and the factor of cost or economics. Change one and all the others are affected.
With the wind-up phonographs that were used for reproduction only, it was desirable that the speed be about the same for all records, but it was not really important since the speed of the player was adjustable. The same situation existed with the first motor driven units -- the speed was manually adjusted until the sound was right for the listener.
In 1925, when electrical recording came into existence, a decision had to be made as to what speed would be used for recording. At that time, Victor was operating at 78 r/min, Edison was using 80 r/min for his disc, while some others were using 82. If Maxfield and Harrison wanted their system adopted by Victor, then 78 r/min was the speed to use. An honest and compelling reason was that Victor's 78 r/min was the predominant speed and it was selected for maximum compatibility between the old and the new. In fact, 78 r/min was selected, but it turned out to be 78.2608 r/min because it was necessary to synchronize the recording turntable to the 60-hertz line and 78.2608 r/min was the only speed at which it could be done practically with a simple worm-gear drive. This, however, is not true for spur gears.
The 78,26086957. . . speed is obtained with a gear ratio of 46 to 1 between the synchronous motor and the recording turntable. This can be achieved with a one-tooth worm gear mating with a 46-tooth driven gear. This is the most direct and simple system preferred for precision work. This speed can also he obtained by a spur-gear train of two 12-tooth pinions, one intermediate 46-tooth gear and 144-tooth turntable drive gear. For 78 r/min exactly, the gears are 13-tooth pinions. 39-tooth intermediate, and a 200-tooth final turntable drive gear. There is not a practical simple worm gear drive to obtain 78 r/min exactly from a 60-hertz synchronous motor.
The 33-1/3 r/min speed came about when Western Electric synchronized motion pictures with records shortly after the introduction of electric recording in 1925. A reel of 35-mm motion picture film runs for 11 minutes. A record was needed to play the same length of time, which was 3.66 times longer than the 3-minute 10-inch 78-r/min record. It was also necessary that the sound be equal to that of the best records. The minimum needle-in-the-groove velocity was 16.33 in/s. To obtain the minimum groove velocity would require, at the end of play of the record under design, a minimum music groove diameter approximately twice that of the 78-r/min record if its speed was to be approximately one-half of 79 r/min. If the speed was to be a little less than one-half, the minimum diameter would have to be larger. Ten inches would seem to have been indicated since the 78 minimum music groove diameter was more than 4 inches. With this determination made, the speed of the record was next in order. Since some difficulty was previously experienced in locking 78 r/min to the line, the motion picture projector people were consulted. What would be a convenient speed approximately one-half of 78 that could be easily locked to the 60-hertz line? The answer was 33-1/3. A simple worm drive with a one-tooth worm and a 54-tooth driven gear or a spur-gear train with 18-tooth pinions, a 108-tooth intermediate, and a 162-tooth final turntable drive gear did the job perfectly.
With this information in hand, it was detemained that 11 minutes of playing time would require 33-1/3 grooves for each minute or 366.6 grooves. At 75 grooves per inch, a music groove band or area on the record of 4.884 inches wide was required, or an increase of 9.77 inches in diameter over the minimum music groove diameter, for a total diameter of 19.77 inches. This meant that a 20-inch diameter record was required.
Increasing the groove pitch over the very conservative figure of 75 per inch used in the trial calculation gave the additional record area needed for limiting the maximum music groove diameter of 19-1/2 inches on the 20-inch record to provide a guard band at the circumference. This, in essence, is the story of the origin of the 33-1/3 r/min record speed.
For the 33-1/3 12-inch LP, only the arithmetic is different. For a 23-minute record, 766 grooves are needed. At a pitch of 300 per inch, this is a music groove band of 2.553 inches wide for the maximum music groove diameter of 11-1/2 inches on a 12-inch record with a 1/4-inch guard band. This leaves a minimum music groove diameter of 6.394 inches; more than needed but found useful for progress. On the basis of such a calculation, the decision was to stay with the 33-1/3 r/min speed. The average wavelength for the top frequency reproduced was 0.0055 inches for the 78 r/min compared to 0.0012 for the 33-1/3. The improvement in compound had more than offset this difference.
The story of the 45-r/min single can be told more briefly. The commercial policy decision was to have a 7-inch high quality fine groove 5-1/2-minute single record plus other features not relevant here. In this instance, all of the design variables except the speed had been established. The arithmetic said 45 r/min. No other figure would fit. The selection of this speed was a well-considered determination in every instance and not the product of caprice. However, there is another -- shorter -- version of how it was chosen: 78 minus 33 equals 45.
Did the war of the speeds cause record sales to dive from 1948 to 1950? It is true that during 1948 and 1949 and for a while thereafter, when Columbia and RCA introduced fine groove records, sales in the United States did turn downward from a continuous upward curve. Then, when RCA in 1950 began releasing records on both speeds, and when Columbia did the same in 1951, record sales soared again. The other and more important half of the story is that during the introduction of the new speeds, the U.S. was experiencing a post-Worid War II depression with increasing unemployment. frequent layoffs, federal government expenditures reduced by 60%, and per capita income decreased by 7%. The downwind turn of record sales coincided with these conditions. In 1950 almost simultaneously with both companies releasing records on both speeds, a conflict started in Korea. Expendable income became more plentiful and record sales responded accordingly. After factoring out the effect of the national economy, the battle of the speeds could not have been heard even around the block. For better or worse, the record industry is not a world unto itself. . . ."
- 1999 by Steven E. Schoenherr. All rights reserved.
Return to Recording Technology History Notes | this page revised Dec. 3, 1999