This is another reason I love level controls for individual drivers.
BASIC: Use SPL meter on tripod, test tones: get best balance, individual speaker drivers, then re-adjust when both playing IN THAT SPACE. Do some, go to bed, finish in the morning, not easy but results are outstanding.
Then, using musical content refine Frequency Balance and Imaging looking for 2 basic factors:
You must have LPs done by superior engineers, excellent mic setup, and location of instruments/vocalists
MALE: I listen to Richard Burton; Tony Bennet; John Hiatt; Paul Rodgers, Simply Red... i.e. do they sound correct, clearly: their voice, it is surprising how this easily reveals basically ’wrong’ or ’right’.
FEMALE: Next, I move on to women for imaging. Of course their voice has to be ’right’ like above, but then, as the frequencies vary, low to high, say Cassandra Wilson; Annie Lenox; Barbra Streisand ...
There can be no deviation from center, no specific frequencies wandering slightly left, or slightly right relative to the general center (from speaker drivers), which will weaken Imaging. IF ’right’, then they and every instrument/vocalist will be properly/tightly located left or right without slight wandering. You get awesome imaging.
This is why I choose cartridges wide channel separation and tight center balance as well as frequency linearity.
This can also be important when playing MONO Lps. Proper MONO cartridge produces clear distinction of individual instruments, not imaging, but distinction. IF frequencies wander a bit left to right, a partial/false sense of imaging can occur, unlike stereo, now weakening the distinction.
Example: I have LP with MONO recordings from the 20’s and 30’s. I played it with a Stereo cartridge, it came off as a history lesson. Early Louis Armstrong: where’s Louis? I would never listen to it again.
Then I got my Grado Mono cartridge: now, what I described, there’s Louis, that’s a Trombone, that’s a SAX, the distinction of individual instruments was very enjoyable. Also, noise is reduced, essentially by half when no inadvertent vertical noise is mixed in (warps, scuffs, dust in grooves .....
