I remember how precise Snell’s were. Proper matching of frequencies L to R is Vital to excellent Imaging, then and now. I suspect Harbeth and Joseph Audio (among others) benefit from those skills.
I’m a big fan of L-Pads to adjust speaker’s in the particular space they end up with, however, I have to work very carefully with my SPL meter and test tone CD to 1st match L to R and then adjust when both playing, the combined output must be refined. Last time it took me 1-1/2 days to ’get it right’. They never sounded better.
Meanwhile, my office, my AR-2ax have level controls, I set them by ear, took a few minutes, good enough, done. I get excellent imaging, if I didn’t I’d get my tools up here.

