Vintage DD turntables. Are we living dangerously?

Taking a break from applied technology, how about remedial physics?
What do MPH and RPM have in common?
Time is a dimension we have divided precisely, based upon, but not dependent upon, the movement of Earth around the Sun. Our division of time does not exactly agree with the rotation of Earth and has to be corrected at regular intervals. It could be divided arbitrarily, but the days and seasons might not agree with nature.

The Earth rotates in a counterclockwise (west to east) direction at approx. 1040 MPH at the equator. If you went to Brazil near the equator and drove a car 100 MPH west, you'd actually be going backwards at 940 MPH and wind up in the Atlantic ocean?

Rotational speed of an object on Earth is not dependent on the rotation of the planet. Either is land speed. As long as we have precise and agreed upon divisions of time and distance, the rotation of Earth could cease and we would still be able to apply our divisions of time. We would still be able to play a football game, do the dishes and take a walk, weather permitting.

Fleib.

The error resulting from record eccentricity is surprising.

Take a small 0.5mm eccentricity on a 100mm radius and we get around a 1% error. (The tracking radius makes a difference)

Nakamichi were on to something way back then.

Halcro, thank you for taking the time to confirm that my original assertions on the disadvantage of using a test record to measure Wow and Flutter were correct.

10-23-15: Dover
3. Using a record with a fixed tone is prone to error. Any eccentricity or imprecision in the surface of the record will generate wow or flutter.

As Marcus Ribi from Feickert says..

10-26-15: Halcro
.. Marcus Ribi from Feikert Platterspeed
The approximate sine wave form of the chart is resulting from eccentricity of the record. A normal measurement of WOW and flutter with a perfectly centered record will NOT show such a wave form, but a more random spiky form instead. That's what the spikes are coming from: it's a superposition of eccentricity and "real" WOW and flutter. Measurement of WOW and flutter then tries to best filter away the regular changes comig from record eccentricity to provide best results.

In the final analysis the key sentence in Feickerts response is "tries to best filter away the regular changes coming from record eccentricity to provide best results". The Feickert software uses algorithms to calculate and remove errors generated by eccentricity. These are an approximation at best.

If you had a faulty turntable with a regular error with each rotation, the averaged WOW & Flutter reported could understate the true WOW and Flutter if the algorithm ascribes the resultant speed issue generated by the fault to eccentricity".

10-26-15: Richardkrebs
Fleib.
The error resulting from record eccentricity is surprising.
Take a small 0.5mm eccentricity on a 100mm radius and we get around a 1% error. (The tracking radius makes a difference)
Nakamichi were on to something way back then.

Assuming for arguments sake that this number is correct, then given that record spindle diameters can vary from 7.09 to 7.21 then we are looking at errors of 0.2% even before we take record eccentricity into account.

Richard, given that most records are eccentric to some degree, could you explain why you have increased the horizontal mass of your ET2 by 300% adding lead to the spindle and removing the decoupled counterweight, when it is clear that increasing the horizontal mass will increase the wow and flutter on playback by a significant degree on eccentric records. The testing I did on my ET2 with removing the counterweight resulted in audible degradation of the sound.

Dover.

Yes "removing the counterweight" would result in a dramatic degradation of the sound!

As to increasing the horizontal mass of my arm by 300%. One needs to specify at what horizontal frequency this measurement is taken.
At 0.55Hz (eccentric record at 33 1/3 rpm) the leaf spring on the ET2 counterweight is stiff. IOW on a standard ET2, at a horizontal excitation of 0.55Hz, the mass of the counterweight assembly must be added to the weight of the spindle, wand and cartridge. This means that when tracing an off centre record, my cartridge sees more or less the same mass as one mounted on a standard ET2. (applies to average weight cartridges and associated counterweights)
BT has confirmed this and I posted his response on the ET thread, maybe you missed this?

Resonance transmissibility theory 101

cheers.