Meh37
@verizon.net
| reply to birdfeedr
Re: Friday Night
said by birdfeedr  : Remember the velocity of the medium is faster in the center than the edge. Actually, it's the reverse. An LP spins with a constant angular velocity (RPM remains a constant 33 1/3), so the outer edge moves faster than that near the center. The linear velocity decreases as the needle moves from the edge to the center. |
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MrMoody
Under the black helicopters
join:2002-09-03
Smithfield, NC
 ·Embarq
| said by Meh37 :
Actually, it's the reverse. An LP spins with a constant angular velocity (RPM remains a constant 33 1/3), so the outer edge moves faster than that near the center. The linear velocity decreases as the needle moves from the edge to the center. Right, and a good example of why Wikipedia is not an authority.
33-1/3 was chosen originally to make 1 inch of grooves at 100 grooves per inch (the effective pitch of the screw driving the recording needle times the gearing) take exactly 3 minutes. At exactly 1.8 seconds per revolution, it's also exactly 108 cycles per revolution at 60 Hz and 90 cycles per revolution at 50 Hz which may have had something to do with the choice as well. It was designed in the 1920s for film soundtracks, and the exact power frequency multiple might have made it easier to adjust the speed in both Europe and the States.
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The public is a poor business manager. |
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birdfeedr
Premium
join:2001-08-11
Warwick, RI
 ·Verizon FIOS
| said by MrMoody :Right, and a good example of why Wikipedia is not an authority. 33-1/3 was chosen originally to make 1 inch of grooves at 100 grooves per inch (the effective pitch of the screw driving the recording needle times the gearing) take exactly 3 minutes. At exactly 1.8 seconds per revolution, it's also exactly 108 cycles per revolution at 60 Hz and 90 cycles per revolution at 50 Hz which may have had something to do with the choice as well. It was designed in the 1920s for film soundtracks, and the exact power frequency multiple might have made it easier to adjust the speed in both Europe and the States. Wikipedia isn't an authority, but I like it for it's fair presentation, and the fact that it continues to evolve.
Except for the quote (which was not in the proper context for this discussion) in my original post, all the rest was my own thoughts re: the physics of recording and playback, and why the 33-1/3 was originally chosen. I got the relative velocities backwards, not the wiki.
Your explanation makes more sense, and it's why I will treat it as authoritative, until something more authoritative comes along. 
Thanks for sharing your knowledge. |
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