It depends on what you are measuring FOR. Rick's right in that the distance from the center/front of the woofer to the floor, to the side wall and to the rear wall matter (theoretically). You're not supposed to have any two of those the same, IIRC.

I'd agree that when most people are talking about distance "behind" the speaker, they are probably talking about from the wall to the back of the speaker. A foot is way plenty for the ports.

Most people think a little toe-in can be beneficial. You just have to experiment in your room.

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