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The length of a 20:00 groove   


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  27th Jul 2021, 8:41 AM#1  REPORT  
Break-In Master

Member since Dec 2013
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How many feet is in an album groove that plays 20;00?
The problem is, the groove at the outermost is 37.700 inches but, each spiral inside of that is a fraction shorter so, you can't multiply 37.700 times the number of rounds it'd take to track the entire length of the groove.
33.3 x 20 = 666.
So, 666 x 37.700 = 25,108.2 inches! That's 2,092.35 feet! 697.45 yards That's just under half a mile. That means that I can actually walk the length of a 20;00 groove in just under 5;00!! BUT, that's IF that number I got is accurate!
But, as I said, with each round, the spiral gets a tad shorter so, that 25,108.2 is inaccurate!
The only way I can think of to get an accurate measurement, assuming the wheel isn't going to slip at all on the surface of the record, is to get a much tinier version of one of those measuring devices they put on the back of a car (a bicycle wheel attached to a kind of odometer) that can be attached to the front of the needle playing said record.
I would think a manual turntable would be best so that It could be stopped at the very end or just before, at which point, you could just spin the record by hand until you get to the absolute end of the groove. It might also be more advantageous to use a record that plays from the inside out.


  27th Jul 2021, 9:17 AM#2  REPORT  
KeithS SUBS

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https://math.stackexchange.com/questions/2805803/estimating-the-length-of-the-groove-on-an-lp


  27th Jul 2021, 11:43 AM#3  REPORT  
Break-In Master

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KeithS wrote:
https://math.stackexchange.com/questions/2805803/estimating-the-length-of-the-groove-on-an-lp
Thanks! Checked it out and responded.


  28th Jul 2021, 9:13 AM#4  REPORT  
carryonsidney

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Spiral calculation
L[enght] = 3.14 x Rx(D+d) /2

R= number of rings, in this case 33 rpm x 20 min = 660

D = outer diameter
d = inner diameter

ergo
3.14 x 660 x D+d
divided by 2
= length of spiral



Edited by carryonsidney on 28th Jul 2021, 9:23 AM

  28th Jul 2021, 11:28 AM#5  REPORT  
kab2112 SUBS

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Not alotta people know that !!!!!


  28th Jul 2021, 4:34 PM#6  REPORT  
getalife

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Member since Nov 2010
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kab2112 wrote:
Not alotta people know that !!!!!


Hang on a minute, lads. I've got a great idea.

For all my education, accomplishments, and so called 'wisdom'... I can't fathom that one out. M.C.



  29th Jul 2021, 1:28 AM#7  REPORT  
Break-In Master

Member since Dec 2013
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carryonsidney wrote:
Spiral calculation
L[enght] = 3.14 x Rx(D+d) /2

R= number of rings, in this case 33 rpm x 20 min = 660

D = outer diameter
d = inner diameter

ergo
3.14 x 660 x D+d
divided by 2
= length of spiral
Yes, but the correct speed is 33.3 so, the number we're looking for is 666, not 660.


  29th Jul 2021, 1:52 AM#8  REPORT  
Break-In Master

Member since Dec 2013
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Nearest I can figure, if we can measure the width of the record from the outermost groove of the music, then get the circumference of that then do the same for the inner-most groove of music and get the circumference of that, then find the average between those two final numbers, and multiply that by 666, that SHOULD give us the number we're looking for!!
As most albums start and end in about the same spot no matter how long the record is, pretty much any album will suffice to take measurerments from.
I asked this at another public site two days ago and had one guy ffactor in the measurements of the labels, the playing surface of both halves of the record (he was going at it via a cross-section and I told him there's no grooves on the label, unlless we're talking about a Jack White album.), the inner and outer lead-in/out grooves, etc. Another seemed to be factoring in the speed at which the needle travels through the grooves (about 5.45" per second).
Just pulling numbers out of the air for what I THINK the inner and outer measurements would be, I ASSUMED the average length of a groove would be 25.5". One of the others, who was a bit more methodical about it, came up with pretty much the same number! (GOD, I'm good!!)
As I DO have a few dozen albums here (they mostly belonged to grandma, this was originally her house. All of my records that I was able to rescue from my house are still in storage.),I'll see a about taking measurements from one of them in a bit but, as I've only got standard house rulers that only go to about 1/16 of an inch, it might not be that accurate.


  29th Jul 2021, 7:26 AM#9  REPORT  
getalife

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Just a thought, would it depend on how many tracks are on the album and the space between each track, would there be a difference with such albums like The Who Sell Out album A side which is one continuous track with seven tracks.


  29th Jul 2021, 11:23 AM#10  REPORT  
Break-In Master

Member since Dec 2013
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getalife wrote:
Just a thought, would it depend on how many tracks are on the album and the space between each track, would there be a difference with such albums like The Who Sell Out album A side which is one continuous track with seven tracks.
It would if we were considering the rills but, I'd prefer an album side with one long track and no rills but, I figure that, as most albums have roughly the same playing area even if they're 18:00 because, the shorter the music, the wider they can space the grooves, pretty much any ordinary album around 20:00 will work.
Besides, the only way you're going to get pin-point accurate is with a microscope and the equipment to show EXACTLY which revolution and EXACTLY WHERE the music ends.


  29th Jul 2021, 11:32 AM#11  REPORT  
Break-In Master

Member since Dec 2013
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I measured the inner and outer diameter of records playing surface a few hours ago.
Outer 11 7/16"
Inner: 4 11/16"
If I can find out how many inches around those are, I can easily find my answer!


  29th Jul 2021, 5:57 PM#12  REPORT  
Hawkmarty SUBS

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Don't forget that on the micro level the sides of the groove undulate so the length could be orders of magnitude greater. What that formula is measuring is the length of the spiral peak.


  29th Jul 2021, 6:04 PM#13  REPORT  
Break-In Master

Member since Dec 2013
250 Points
Hawkmarty wrote:
Don't forget that on the micro level the sides of the groove undulate so the length could be orders of magnitude greater. What that formula is measuring is the length of the spiral peak.
I don't know that iit matters that much. What about something like "Marcel Marceau's Greatest Hits" where the entire side is completely blank except for the last minute, which is applause. Okay, each side is only 18;00 (I have a copy) but, it still takes up roughly the same amount of space. Just because the grooves are blank doesn't make the playing area any narrower.


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