Phase can (and will) become an issue (comb filtering depending on the listening location) when you play phase coherent signals over more than one speaker. For m

Phase can (and will) become an issue (comb filtering depending on the listening location) when you play phase coherent signals over more than one speaker. For most home applications this might not be a big issue tho if you don't have a totally unconventional speaker setup. If each speaker plays something else you are good (depending on how uncorrelated the signals are). If you need to add extra speakers to "extend" an existing set of speakers (e.g. on a huge stage) the phase correlation of those extension speakers will be critical. That means, ideally you want the extension speakers to "fire" exactly at the moment when the wavefront of the original speakers hits. That means you have to delay the signals for the extension speakers by the time it takes the wavefront to travel from the original speaker to the extension speaker (influenced by distance and air temperature). One thing to consider about phase as well is that the same thing in reverse applies to recording as well.