The Secret Society of Lathe Trolls

blight · Joined: 19 Jul 2006 Posts: 48

... does it make sense to try to calculate them?

I made some charts (dotted lines are without RIAA, dB levels in reference to 8cm/sec effective lateral velocity, those charts are only for mono, not stereo):

Frequency vs. Max level vs. Radius (at this level the maximum cutting/groove angle should not exceed 45°)

Frequency vs. Amplitude vs. Level

Time vs. Max amplitude vs. Space available (this is the max amplitude if you want to cut a certain amount of time on a certain space - at this amplitude grooves shouldn't get closer together than 10µM if their width doesn't exceed 50µM - the groove spacing is twice the amplitude + 60µM)

And the same for 45RPM

andybee · Joined: 14 Aug 2006 Posts: 63

hey! this is VERY cool!

Cool

blight · Joined: 19 Jul 2006 Posts: 48

You really think its cool/useful?

I don't know if the charts are right because I don't have much experience with cutting records (so I don't have a "feeling" for the levels etc) and I am not very advanced at maths so I am not sure if I got the formulas right.

Maybe you want to discuss the formulas? Smile

Steve E. · Posted: Wed Apr 04, 2007 1:29 pm Post subject:

This IS cool. I don't have enough experience either to know how accurate you are. But yeah, I hope people discuss this stuff.

JayDC · Posted: Wed Apr 04, 2007 1:41 pm Post subject:

maybe a better explaination of this information is in order. I see what I'm looking at, just don't know why I'm looking at it..

blight · Joined: 19 Jul 2006 Posts: 48

Ok, here are some formulas which i used to make those charts...

For the last chart (time vs. amplitude vs. space) the formula is easy:

number of grooves(rounds) = rpm(rounds/minutes) * time(minutes)
groove spacing(µM) = total space(cm) / number of grooves(rounds) * 10000
maximum peak amplitude(µM) = (groove spacing(µM) - 50(µM) - 10(µM)) / 2

50µM + 10µM are substracted from the groove spacing (50µM for the width of an unmodulated microgroove, and 10µM as minimum spacing between the grooves)
The result is divided by 2 to get the peak value (otherwise it would be peak to peak)

For frequency vs. amplitude vs. level it's not so easy anymore...
0dB are specified as 8cm/sec lateral effective velocity. So how much amplitude would it need for a sine wave to produce an average 8cm/sec velocity at a certain frequency?
I found this formula on the net:
Veff = 2 * PI * amplitude * frequency
thus
amplitude = Veff / (2 * PI * frequency)

0dB at 1kHz = 8cm/sec / (2 * PI * 1000) = 12.73289256303577624 µM

And for frequency vs. level vs. cutting radius:

First we need the speed of the disk under the stylus:
speed(cm/sec) = 2 * PI * radius(cm) * rpm / 60

now we can calculate the amplitude of the sine wave for which the groove will not be steeper than 45°...

for a certain frequency, one period is "speed(cm/sec) / frequency" cm long.
length(µM) = speed(cm/sec) / frequency * 10000

I don't know the correct mathematical explanation for the following, but i think it's right...
For a sine wave whose period is 2 * PI long and whose amplitude is 1, the steepest angle (at the zero-crossing) is exactly 45°
So if it's 4 PI long, the amplitude can be 2 for a maximum angle of 45° at the zero-crossing.

Thus:
amplitude(µM) = length(µM) / (2 * PI)

All those formulas are without RIAA taken into account (the dotted lines)
For RIAA you just add (or substract) the dB values from the RIAA curve...

JayDC · Posted: Sat Apr 07, 2007 9:37 pm Post subject:

WoW!...

Using this formulation I was able to cut at +6db @ 2.2vac with a 184LPI lead screw. All this with the presto 1-C head. Good levels all through 25hz-15Khz, my loudest best sounding record to date. Twisted Evil

Thanks for the great info... Very Happy