I have some technical questions about ports.

I noticed in the 360 degree view of the center speakers that they don't have a port. Since all of the towers and bookshelves, except the MZeroti, have a port, why don't the center speakers? What is the impact to the sound of a speaker with a port vs one without a port?

Along that line, why do the towers have ports in front and back? Does this make them easier or harder to position, expecially in tight quarters, like between the side of an entertainment center and a wall where you may only have a foot or two of room? What would be the difference if the speaker only had a single larger front port?