Re: Why were the rpm speeds of records chosen
According to Wikipedia, 78rpm was arbitrarily chosen as a standard once record players started using synchronous motors so would have a well regulated fixed speed. Most early records were anywhere between 74rpm and 82rpm and you just altered your gramophone to make it sound right.
33⅓, 45 and 16⅔ were standards produced by different record companies, though no explanation is given for why they chose those speeds. I would guess that 45rpm was chosen as being easy to derive from a 60Hz supply maybe.
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