Randyman, you are certainly on the right track. For an in-room environment, and especially with low frequencies, you will end up with canceling and doubling happening to various degrees around the room. This effect is not really related to the interaction between the different driver components though. In the initial speaker design the interaction between the drive components will show up as a doubling or a canceling exactly as you have pointed out, in an anechoic environment. This needs to be dealt with during the design of the speaker initially.
