Measuring turntable speed
As an aside, is turntable speed all that important. I think not as important as speed variations like wow and flutter. The absolute speed could be off 1 or 2% and most of us myself included would not know.For once we agree on something! How many here are going to claim they can hear the difference between 33.30 and 33.40 say as long as speed is constant? Have a great day! |
https://i.imgur.com/Lo0LYl1.jpg This is good enough for me and the DIN standardisation. 3150 complete sine waves in one second. Is more than a strobe disc can ever do. And the lack of the high granularity we can not get the speed variation either. Now we get graphs with the better resolution. Regarding the lathe machine speed accuracy precision. It starts to get more silly and pointless the more number 3:s we add to the end of 33.3xxx. And yes we measure with the diamond in the groove. That someone asked. |
Fun gear! So you put one reflective strip on the edge of the platter. And you lay the device down so you don't hold it (movement of holding it introduces in its own fluctuations). But if we stop and think about it a second. Manufacturer of TT measure and specify speed as wow and flutter. This measurement quantifies the amount of 'frequency wobble' (caused by speed fluctuations)Source: https://en.m.wikipedia.org/wiki/Wow_and_flutter_measurement So let's look at the "speed fluctuations" that a DT-2234+ digital tachometer can capture: At 33⅓ rpm the platter has done little more than a half rotation. And you need to wait almost another half turn before you get the next measurement. With out taking into account the variance of the tachometer itself ± 0.1 rpm. (33⅓ rpm / 60s = 0.5555 RPS) So almost 2 seconds between each measuring point. During the elapsed 2 seconds the "speed fluctuations" can easily have been momentarily fluctuate between +0.25% AND -0.25%. But that fluctuation is something you don't pick up and totally miss during the ~2s wait.. we only get a average over those ~2s. Here is a example of how rapidly the speed is fluctuate during 2s if we use a better method with a greater resolution: https://imgur.com/a/Vmz7CrU Measurement is usually made on a 3.15 kHz (or sometimes 3 kHz) tone, a frequency chosen because it is high enough to give good resolution, but low enough not to be affected by drop-outs and high-frequency losses. Ideally, flutter should be measured using a pre-recorded tone free from flutter.Source: https://en.m.wikipedia.org/wiki/Wow_and_flutter_measurement As seen in the Imgur link above in this post we here measure EACH 0.1s something that have 3150 samples each second.. It a whole lot another resolution that a stroboscope never ever can give you. Yes, why is this useful? Is it not lunatic? This resolution enable you to see if you get less fluctuation if you add a standard 500g clamp (center/ring)... Will a 500g addition that add the rotating mass (inheritance) to make your platter to fluctuate less? With a strobe you will NEVER know.. You can also catch if your speed is drifting or is rock stable the same after a week or so. Small shanges is impossible to capture otherwise. Like when changing belt or maintenance with oil change and so on.. All you need is a calibration disc/LP (that you can calibrate other things also with). And a vinyl lover have to have one of those anyway! And a old discarded android phone $0 (or your present one) and just download the app. (See my previous posts) You can save and load measurements and compare them. Of course you can adjust the speed on the 45rpm also. So why pay money for a stroboscope when you can buy a test record instead that with the other tracks you can measure other things.. the strobe can only measure one thing and that is done rather poorly relatively compared to the standard way of doing it... I don't believe that I am smarter than the girls and boys behind standardisation institutions like specifications (that use a variant of this procedure):
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