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

I’ve been a pro musician since the 60s, and I’ve learned that there is no bottom line regarding level. After years of hurting people with my trusty JBL festooned Twin Reverb with a Tele or Les Paul I switched to various smaller amps pointed at my ears and miked up appropriately. Still loud for me, perhaps not so much for you. I’ve also spent plenty of time in studios and as a live concert mixer and, again, there’s no bottom line for level...live I just want things to sound good and clear. I spent an afternoon in the 70s watching Glynn Johns mix and it was so loud I think I suffered some hair loss. At home all hifi level is mood based and it seems silly to try and quantify that...only play it loud if I need to hear something from the next room.

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.