[78-L] Record playing speed ^

[Chris Zwarg]

At 17:25 03.12.2008, you wrote:
>At 09:32 AM 12/3/2008, you wrote:
>>And is 160 rpm the standard speed for cylinders?
>
>Yes I suppose so but why did they go so fast instead of something like 80 rpm?

Because the circumference of an ordinary cylinder is only about half the diameter of a (rather small) disc groove, so you need at least double the rpm to get similar fidelity. If you have ever listened closely to a "Little Wonder" or similar miniature disc you will have noticed how the treble response and overall volume breaks down towards the end, when the groove diameter gets too small. A good acoustic recording has a frequency range of roughly 4 kHz, so you need to register up to 4,000 undulations per second, stretched out wide enough that the playback stylus can track them. If your groove diameter is small (like on the standard two-inch diameter cylinder) you need high rpm to get enough space for clear sound. A groove with a larger diameter needs fewer rpm for the same audible result - that's what 5-inch-diameter "concert" cylinders were developed for in the late 1890's. 

The same reason explains why 33 1/3 rpm transcription discs were so large and usually had pretty big unrecorded label areas: Trying to crowd 15 minutes of programming on a 12-inch disc using 1930's groove-size and styli caused an unacceptable drop in sound quality towards the end of each side. As you all know, LPs use much finer styli that allow smaller soundwaves to be traced accurately, so they can afford to run at the lower rpm without loss of fidelity.

Chris Zwarg