Macg19. Sorry I wasn't clear. What I meant is our ear's balance changes with level. The louder we listen the closer lows and highs are to the mid levels. But this doesn't imply we should listen at 100dB. But the nearest to correct balance(assuming good recording engineering) will occur when the level at one's ears is the level the recording was balanced at. But complicating that is how linear level changes are in a system(due to speaker dynamic linearity and the relationship of amp/speaker and to some degree the rest of the system. If it's right at one level and the system compresses above that it will be wrong at higher levels.
Anyway listening at the ear at low levels makes the bass and treble sound lower than they were recorded at relative to the mids.