Bernard's not talking about which wire is which between (+) and (-) (yes they do have to be in phase) - but directional wire where it supposedly matters which end of the cable is which!

Speakers are AC, but they still have to be in phase with each other. So for a mono signal, when one side is getting a positive half cycle, you don't want the other side getting a negative half cycle. Or in more physical terms, one cone pushing while the other is pulling!

Don't be confused by the + and - markings on the terminals - that doesn't means they use DC. It's just so if you match up hot to + on both channels they'll be pushing in the same direction.

Anahata