Are you operating in the correct SPL window for high-fidelity listening?

I’m listening at 66db now which is optimal for me when I am not constrained by other people or nighttime situations.

Again, what meter, what weighting, what type of speaker (planar vs cone), how are you aiming your meter, what distance from the speaker, what angle with respect to the speakers??? All of these things dramatically affect the meter reading. Therefore, none of the above data have any meaning that others can draw from them.  But I am sure every contribution is meant to be helpful.

I use an old Radio Shack SPL meter set on C weighted and on slow.  I measure from my seated position on my systems:  always an equilateral triangle.  I understand that not all instruments measurements are as accurate as others, but even a iPhone gives you a good idea, even if it does not measure SPL below 50hz. The differences cannot be so substantial that they cannot be compared.

My fault for not asking a clear question.  I wonder if others have found a minimum volume where the bass, midrange and treble all sound the same volume.   An effort to overcome the Fletcher-Munson curves and make the audio spectrum sound flat.

roon tends to do a good job maintaining comparable listening levels however I think all this loudness stuff is recording specific.

Quality of recording plays a big role in how the music fills the room.  

And of course the louder the music the more damage likely to your ears. And damage to your ears is cumulative.  That’s why beginning to smoke a really bad idea.