Direct Drive turntables

"but this is a place where subjectivity rules. IMO, measurements are useful in guidance, i.e. don't buy a 2W SET amp if your going to use 85dB efficient speakers, but the only thing that really matters is how the equipment meets your individual requirements to connect with the musicians."

Right on!

Here's an objective test that might be done.

If one were inclined and had the knowledge and time, one should be able to take a high res digital file created from various turntables as a source and then use computer algorithms to match the signal produced there to an all digital reference master of the same material to discern the differences. Then the question would become what accounts for the differences that would surely be observed.

This would be a fun project. Maybe someday after I retire and need something to keep me busy in addition to current hobbies, including just listening to and enjoying music.

Any EE students out there looking for a masters thesis perhaps?

They are not as common because they are more expensive to do well these days as someone indicated early on.

I'm skeptical of any inherent benefits of DD to the average home record listener over other drive approaches. It ain't rocket science to get a table to spin at constant speed and there are lots of ways to do it cost effectively. ISolation from motor or other external vibrations is trickier.

For good sound, better to focus on matching a good cart to good arm and phono pre-amp optimally.

Changing drive alone would be a purely academic exercise, except for perhaps for those that might be willing to custom build their own table.

Practically, it is the overall design and integration (table, arm, cart, phono pre-amp) that matters for most. Any type of drive mechanism, if done well, will work just fine.