DragonDiscs - Vinyl Collectors Guide and Resource Kit

Some Interesting Figures on the Mathematics of LP's

Well, bad weather in the North East has caused classes to be cancelled yet again, so I figured what better way to spend my day than reading/writing about vinyl.

I myself have always been amazed that the LP or 45 work nearly as well as they do. When you think about it, the micro groove is pretty tough obstacle course for a stylus, and I have always been amazed that it doesn't wear out faster.... Anyhow, I was searching for something to occupy myself with, and came up with these numbers:

Though an LP is 12 inches in diameter, when you cut out the label, and the lead in/ trail out grooves, there are actually about 3 1/8 inches (8cm) of linear recordable space. Considering that an average LP is about 22 minutes per side, that averages out to 733 concentric grooves per side. If you divide that by the recordable space, you come up with 234 grooves per linear inch (9.1 grooves per mm!!!!) That figure seemed somewhat amazing to me, as I was expecting possibly 2-3 grooves per mm. And, this figure does not account for space wasted by inner track grooves.

Another facet of recording that I found interesting was the vibrations per linear inch in the groove depending on the frequencies recorded. Considering that an LP spins at 33 1/3 rpm, it takes 1 4/5 seconds to make 1 revolution. At the outer edge of an LP, this converts into 20 inches per second (52cps) spinning past the stylus. That means that a 20khz tone has vibrations approximately 1/1000 of an inch (.02mm) apart. This figures become somewhat more amazing at the inner tracks of an LP. The inner most groove recorded on most albums is about 5" (13cm) in diameter, which translates into only 8.72ips (22.68 cms) -- much less than half the speed of the outer tracks. Here, a 20khz tone has vibrations every .00044 inches (.011mm) --Now that's tracking accuracy.

Just a little educational titbit -- come on, somebody else finds this interesting -- don't they?? Hmm...or maybe I'm alone again on this one.

Submitted by Alex Rovnan