Phase Cancellation and the L1
Minimum Distance Running Two L1®s in Dual Mono
Phase cancellation can be an issue if you are running Dual Mono (two L1®s from the same mono source). This can be an issue when two or more L1®s are fed the same signal.
The minimum recommended distance for two L1®s running the same signal is 20-50 feet.
Only when fed the same signal, "Interference between line arrays would be more severe [than for non-line-array speakers]. In fact, the current Bose design rules for installing MA12 line arrays recommend ... a spacing between line arrays of between 6 and 15 meters! (20-50 feet)" The same applies to the L1. - Chris-at-Bose  (Clarifications added by the author of the quote.)