My oppinion on this is to get it close but don’t loose sleep over 1/8 of an inch. I also think that sometimes its better to not have them at the same exact distancE from the walls because of frequencies cancelling each other out. Also, your room is probably not perfectly square. I like to do what MC says but then use a string japed to where your head is then pull the string tight to one tweeter. Hold that position on the string now walk over to the other speaker and make it the same distance.
Distance to speakers and equal angles to the speakers is more important than equal distance to walls.
Shoot, speakers are going to have sliggt differences between the drivers and crossover components.
I’ve been using Sonarworks reference 4 correction software and my speakers measured slightly different between the 2 channels. I was within + or - 3 db the whole range but with correction on, the image is perfectly centered and the frequency is flatter. Im not certain the cost sonically speaking though of using this program. A bit too early to tell if its something I will use all the time, part of the time or none.
