Explaining the sizes and speeds of vinyl records

There are some things we don’t really question: the sun coming up in the east; American politics will continue to be dysfunctional; and the Toronto Maple Leafs will once again break hearts next spring.

We can throw a given about vinyl records into that pile, too.

Have you ever wondered why they come in the diameters they do? How about the speed at which they rotate? The answers contained herein could win you a lot of bar bets.

The first format for recorded music was the Edison cylinder, a Coke can-looking thing that rotated along a horizontal axis like a piece of wood in a lathe. It was eclipsed by Emile Berliner’s rotating disc (patent 564,586) in 1888. His discs not only sounded better, but because they had two sides, double the capacity. Within a decade, the cylinder had disappeared.

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But even as the idea of flat rotating discs caught on by the turn of the 20th century, there was little in the way of standards. Some companies made records seven inches in diameter. Others felt that 10 inches was better. Still others went for 12-, 14-, and even 16-inch discs. In 1904, a British company called Neophone began issuing records that stretched 21 inches across. The bigger the disc, the more music it could store. Complicating matters were the discs that played from the inside out instead of vice-versa. Of course, not all turntables could handle the peculiarities of all the records on the market.

Width was only one way to determine capacity. Another was the speed at which the disc turned. There was considerable disagreement about this at the beginning. Berliner designed his original Gramophone to play discs “at about 70 RPM.” The reason for this approximation was that this was before the age of electric motors in turntables. Spring-wound mechanisms provided the power and were notoriously inaccurate.

Other turntable makers jumped into the market and also made their own records, and also chose to have them spin at different speeds, ranging from 50 RPM all the way up to 120. Early audiophiles shelled out extra money for turntables with variable speeds so they could match up their device with any record they purchased.

Eventually, though, pretty much everyone settled on a 10-inch 78 RPM design by the 1920s, influenced largely by an industry handbook (written by … someone; no one is really sure) that really seemed to like that speed, asserting that it provided the best level of sound, the optimum capacity per side, and the least amount of wear. It was at least a start.

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By the time we got to the 1920s, turntables were powered by electric motors. It should be simple to build something that drove a platter at exactly 78 RPM, right? Well, no. The motor chosen by a majority of manufacturers ran at 3600 RPM with a gear ratio of 46:1. Divide 3600 by 46 and the effective drive speed of the motor is 78.26 RPM.

But even this wasn’t completely standard. The true speed depended on the electricity supply of where you lived. In Canada and the U.S., power came out of the wall at 60 hertz at 120 volts. In the U.K. and Europe, the standard was 50 hertz at 220 or 240 volts. This meant that our turntables ran at 78.26 revolutions per minute while in Europe, they turned at 77.92 RPM. Average that out and you get 78.09 RPM. Therefore, that became the standard for manufacturers, even as engineers worked out a way to lock in rotations at exactly 78 RPM.

The 10-inch 78 RPM record ruled until 1948 when the 33 1/3 RPM 12-inch record was introduced by Columbia Records. That rotational speed is exactly one-third of 100, so that must be the reason for that speed, right? Well, no. Just like with its predecessor, the speed story of the LP is complicated.

Along with rotational speed and diameter, there’s a third component to the capacity of a record: How closely the grooves are cut together in that continuous spiral from the outer edge toward the inner label. The 78 had a hard limit on how tightly those grooves could be compacted. Add in speed and diameter, and the maximum capacity of a 78 was around four minutes per side as the needle traced a groove spiral that was about 270 feet long. That was not good enough, especially for fans of classical music where movements lasted for many minutes longer. Who wanted to interrupt Beethoven’s Fifth every four minutes to flip or change the record?

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In 1931, RCA introduced a new type of record just as movies were beginning to have sound. Motion pictures came on standard-sized reels of 1,000 feet of 35 mm film with a running time of about 11 minutes. To match up sound and film, a company called Vitaphone introduced a system that used one of those 3600 RPM turntable motors to rotate a 12-inch disc. To make the audio last the entire 11 minutes of a reel of film, the math said the motor required a gear ratio of 108:1. Divide 3600 by 108 and you get 33 1/3.

RCA tried to market the new records to the general public, but it was the Depression and record sales had collapsed by more than 90 per cent in the space of a year. It was not the right time.

Fast-forward to the late 1940s. RCA’s rival, Columbia Records, picked up on RCA’s older technology just as it was experimenting with a new substance called polyvinyl chloride, a tough type of plastic that had been invented for use in sewer pipes. Vinyl, as it was called, was much more durable than the fragile shellac compounds used to make 78s. Not only did vinyl not wear out as quickly, but its toughness meant that grooves could be spaced much more tightly. Columbia called this “microgroove” technology and also developed a stylus that was much tinier and sharper. Instead of a spiral of 270 feet, the side of an LP carried one that was 1600 feet long. Doing the math (π times 33 1/3 times the outside diameter of the grooves plus the inside diameter divided by two) resulted in 24 minutes of music per side. The 78 was doomed and was phased out by 1960.

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When RCA realized that Columbia had beaten it with its own technology, it was greatly annoyed. Instead of licensing the new tech from the enemy, it vowed to create its own propriety format. The result, debuting in March 1949, was the 7-inch 45 RPM single.

RCA’s thinking was that since people had been perfectly happy for the last 50 years with records that featured just one song per side, why not just give them more of what they wanted but in a better-performing package? RCA’s solution was to come up with its own type of record made out of polyvinyl chloride. And to keep as much market share as possible, these discs were designed to be played on special turntables made by RCA.

But why 45 RPM? Some people insist that it’s a simple case of subtraction: 78 minus 33 equals 45. Nope.

Again, let’s look at some math and geometry. In this case, we also have to concern ourselves with the curvature of the grooves on a record. As the stylus gets closer to the centre, curvature increases and the relative linear speed slows down. In the case of an LP, the platter may still be turning at 33 1/3 RPM (one revolution every 1.8 seconds), but the amount of information stored in the grooves changes. As the stylus travels closer to the centre, more and more information has to be jammed into each groove. The result is an increase in distortion and the loss of high frequencies. (This is a major reason why the best songs and singles from an album used to appear closer to the outer edges of an LP.)

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However, RCA discovered that if a disc spun at 45 RPM, there was a 35 per cent increase in “groove velocity,” which greatly reduced both distortion and the loss of high frequencies. The issue, though is that you have 35 per cent less time for music. But RCA considered that was a good trade-off. They could say that their records sounded better than Columbia’s LPs.

Both formats certainly had their advantages, although RCA saw any hopes of maintaining a propriety hold on 45s by being the exclusive manufacturer of turntables that spun at 45 RPM disappear when other companies started making turntables with three speeds: 78, 45, and 33 1/3.

And we’re still not done. You may have encountered turntables with a fourth speed: 16 2/3 RPM. What’s that all about?

These were low-fidelity records of varying diameters that were used for audio that didn’t need great audio reproduction. They were used for the first audiobooks, especially books read for the blind. They were great for children’s records. If you’re old enough, you might remember records that came with breakfast cereals; these were almost always designed to play at 16 2/3 RPM.

They were also used by restaurants and offices for background music. In this case, music came on 9-inch records that could be stacked on a spindle, like 45s. Each side of a record provided 40-ish minutes of mono, lo-grade audio which was good enough to play behind crowd chatter. Finally, there was the Highway Hi-Fi, an under-dash turntable (!!!) offered by Chrysler and DeSoto in the 1950s. They were quite awful-sounding and drivers were limited to the 40-ish discs they could purchase through dealers, so it’s no wonder the idea never took off. The 16 2/3 RPM record was killed off for good by 8-tracks and cassettes.

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Today, it’s extremely rare to find a modern turntable that can play more than LPs and 45s. Still, there are collectors who treasure their 78s and will search out record players that will serve their needs.

Like I said at the beginning, the history of record rotational speeds is complicated, but now you’re, er, up to speed. Now go win some bar bets.

Alan Cross is a broadcaster with Q107 and 102.1 the Edge and a commentator for Global News.

Subscribe to Alan’s Ongoing History of New Music Podcast now on Apple Podcast or Google Play