The accepted rule by several industry standards is the 60 degree triangle, strictly depending on your listening position relative to the speakers (you obviously sit at the tip of the triangle). In many cases the speakers are much to far apart to obtain proper staging and center fill and toeing them in only compounds the problem. Always start determining proper speaker placement with speakers relatively close together, say 4 feet. The other problem with speaker set up is that many folks believe that speakers need to be wide apart for best sound. It's like trying to solve two simultaneous equations in three unknowns. You might find GOOD locations, even VERY GOOD locations by ear, but you won't find the ABSOLUTE BEST ones. At least the odds are stacked against it. You will never find the REAL ABSOLUTE BEST LOCATIONS, only the LOCAL MAXIMUM locations. You might find GOOD locations, even VERY GOOD locations, by ear but you won't find the ABSOLUTE BEST ones. The problem with trying to do this by listening a little and moving a little is that you will never find the REAL ABSOLUTE BEST LOCATIONS, only the LOCAL MAXIMUM locations. Something like the speaker set up track on the XLO Test CD is required, I.e., a methodological way to find the precise locations for ANY speakers in ANY room. Unfortunately, the precise locations say within a 1/8' or 1/4' for each speaker or whatever is not really achievable by ear. PROPOSITION: It's important to get the speakers in the ideal locations for best sound.

Speaker placement tool