How Long Is That Groove On Your Lp?

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How long is that groove on your LP?

Post by Guest » 06 Feb 2009 06:24

"I'm a needle on a spiral in a groove." (Jethro Tull - 'Something's On The Move')

I've sent a fair number of needles on a fair number of journeys along the sides of a fair number of records without ever before asking myself what I had asked it to endure. Tonight I decided to try to find out, at least in a general sort of way. I first needed a formula for computing the length of a spiral, and after a bit of web searching I found:

L = Pi * N * (D + d)/2

D = outside diameter of the grooves (288 mm.)

d = inside diameter of the grooves (123 mm.) (D and d measured on a genuine K-Tel record.)

N = number of rotations: play-time times record speed of 33.33 rpm.
Assumed play time of 24 minutes times 33.33 rpm = 800 revs (rounded)

Putting the numbers in the formula and solving tells me the record presented a 516,478 mm. groove to the needle. 516,478 mm. is the same as:

516.5 meters, a little more than half a kilometer

1,695 feet, or 0.32 mile

And that's only for one side. If the other side is the same length the needle could then travel 1.033 km or 0.64 miles in 48 minutes. If all albums were this long (0.8 hours) you would be able to play 625 albums before you had 500 hours on your stylus. The needle would have traveled the equivalent of 400 miles through a vinyl canyon before you should be concerned with it's replacement. That is, if all LPs had 24 minute sides, AND, if the formula was right. :crazy:

leitmo
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Post by leitmo » 06 Feb 2009 13:49

wow!

insane ellbee!

i'll think twice before replacing my stylus...and i should start thinking replace my converse

fscl
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Post by fscl » 06 Feb 2009 18:31

Hmmmmmmmm......

Puts a whole new spin on,

"Shake Your Groove Thing".....


8)

Fred

riche_guy
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Post by riche_guy » 06 Feb 2009 19:58

There are other factors that can cause your stylus to wear. Such as dust and dirt in the groves, the weight of the cartridge on the disc, the speed being played 45 or 33?, temperature, dust in the air. So many variables.

JamesBeach
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Post by JamesBeach » 08 Feb 2009 10:06

riche_guy wrote:There are other factors that can cause your stylus to wear. Such as dust and dirt in the groves, the weight of the cartridge on the disc, the speed being played 45 or 33?, temperature, dust in the air. So many variables.
Sure, but in the shadow of 400 miles of travel, unless you're playing discs forged from sandpaper at 78rpm in a dust storm those factors will likely prove statistically irrelevant.

A similar measurement: the fastest commonly available hard drives are of the SCSI persuasion and spin at 15,000rpm. Not directly analogous to records, of course, seeing as there is no physical contact between the head and the platter and you can't really measure the distance a head travels over its lifetime since the design of a hard drive permits random access. However, the length of a track at the edge of your common three and a half inch drive is approximately ten inches. If reading or writing to the outermost track, such a drive will read and write with perfect accuracy to magnetic anomalies measuring in the microns passing underneath the head at about 2.4 miles each minute, or 144 miles per hour.

That's pretty amazing as well.

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