78 minus 33 = 45

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Early Discs

The First 45s

The LP Arrives

Seven inches, 33 rpm

16 and 2/3

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12” 78 rpm record, with advert for speed tester, to check your 78s were revolving at 78 rpm “the speed necessary to ensure true reproduction.”

LPs are usually 12″ in diameter and play at 33 rpm
Singles are 7″ in diameter and play at 45 rpm
Old shellac discs are 10″ or 12″ in diameter and play at 78 rpm

What is the relation betwen those numbers? Why does 78 minus 45 = 33? Is it coincidence?

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The first viable flat discs (as they were called) were made by the United States Gramophone Company in 1893, using Berliner’s 1888 invention. They were single-side, seven inches in diameter, and had a playing time of two minutes. They were sold for 50 cents each (or a dozen for £5). The cheapest model of gramophone was hand-turned and the manual suggested 70 revolutions per minute.

A more rapid motion will raise the pitch and sharpen the sound; a slower motion will deepen the same.
United States Gramophone Company, “Seven Inch Hand Gramophone” manual, 1894

There was also an electric model. From 1900 to 1925, speed fluctuated between models from 74 rpm to 82 rpm. Electric turntables arrived in 1925. The motor ran at 3600 rpm, and was geared at 46:1 giving a standard speed of 78 rpm (in actuality, 78.26 rpm).

33 1/3 was initially used for sound recordings synchronized to the first sound films. They worked out that synchronization with film (which came in 11 minute spools) would need a speed between 28 rpm and 35 rpm. The system was designed by Bell, and was called Vitaphone. The discs were 16″ in diameter, and played in the reverse order to other discs … the stylus started in the middle and moved to the outside.

As with 78s, the most commonly available small electric motor ran at 3600 rpm. There were standard gear ratios available off the shelf, and a common one was 108:1. That gives a speed of 33.33. It works with 50Hz and 60Hz electrical systems by changing the number of poles on the motor .

By 1929, gramophone and record sales were in sharp decline under competition from radio, fuelled by the economic woes of the Depression. RCA Victor piloted a 331/3 Program Transcription record in 1931, with the aim if getting each movement of  Beethoven’s 5th Symphony to play right through. Beethoven remained important … the first CDs were 72 minutes so as to accommodate Beethoven’s 9th Symphony on one disc. They doubled the number of grooves per side,  and used 33 1/3. This gave them fourteen minutes a side

On 78 rpm 10″ discs in 1931, the record side had to be changed every four minutes. They recorded Stokowski with the Philadelphia Orchestra (Victor l-7001) on a 12″ double-sided disc.

A review of that first 33 rpm disc:

The recording is conspicuously lacking in colour, brilliancy and character; it is thin, flabby, faded and lustreless; the music is all there but is pale, weak and lacks the life of the origins.

The system was used for radio show Electrical Transcription discs providing complete shows to smaller radio stations until the early 1940s. Transcribed meant pre-recorded. Sometimes a transcription disc could be paused to allow a live DJ to intervene. I’ve only seen one 16″ transcription disc in the UK, and that was in a glass cabinet with a sign saying NOT FOR SALE.

Early 33 1/3 rpm discs:

RCA Electrical Program Transcription

Flash Gordon transcription 1935

The Amazing Adventures of Flash Gordon: RCA Electrical Transcription Disc, 1935

Superman transcription disc 1941

Superman Transcription disc.  Part of an 18 disc set on 16″ discs. The shows ran from 1940 to 1949. This set was sold at auction for $3,115.

Enter vinyl …

Columbia Records cracked the problem of musical programme length by 1947 under the direction of Peter Goldmark. The secret was a new material, vinylite.  The first discs held up to 300 grooves per inch, compared to 85 grooves per inch for the older shellac discs. They went for the already known 33 1/3 rpm speed.  They could have chosen any speed around that area, but 33 1/3 existed so they went with it. The records went on sale in 1948.


Meanwhile, RCA Victor was developing the 45 rpm record, and on a 7″ record, that gave it the same playing time as a 10″ 78 rpm record. RCA said researchers had found 45 rpm was the optimum speed, but actually they wanted ANY speed as it wasn’t compatible with Columbia’s 33 1/3 system. There was no turntable in existence to match the speed to. They wanted a new and different speed.

SEE also THE FIRST 45s

RCA invested a massive $5 million on the system, but 45 rpm  worked as the medium for popular music. They had to admit that the 33 1/3 format was better for LPs by 1950. At the same time, Columbia started producing 45s.

I still haven’t discovered WHY 45 + 33 = 78. I suspect that RCA worked out that they needed a speed somewhere between 40 rpm and 50 rpm, looked at the 78 and 33 numbers, subtracted 78-33 = 45  and thought “This will confuse them for years to come.”