The Anglo/Irish air "The Wounded Hussar" played on a violin made by Russell Hopper completed January, 2010. This is the same violin pictured in an earlier post on January 21. I've tweaked the response and tone to my satisfaction, mainly by slightly moving the soundpost inside the body. By changing the location of the post's point of contact (within about 2mm in any direction), the response and timbre of each string will change.
Simply said, the belly flexes around the point where the post makes contact with the wood. The hard, less flexible maple back of the violin provides a solid platform for the post to sit on. There are long-standing false theories on how the sound-post works, the most prevelant one being that the post transfers the vibrations to the back. I'll write more about the sound-post later in detail.