a blog by Peter Leonard
By far the trickiest part of this whole process so far is the insertion, after the whole body is glued together, of a small dowel called the sound post. This tiny piece of wood is responsible for transferring the vibration of the front to the back cover. Because of this involvement with resonance, the post can't be glued in place or otherwise fixed through any method other than force and friction. I was a bit skeptical that we could ever size the dowel correctly: too small and it will easily slip out of place; too large and it would never be possible to move it into place from a diagonal position. Somehow it all came together, and gave us our first experience with a special tool called a "sound post retriever." This is a long piece of metal with sharp wedge on the end. After impaling the post on the wedge, you insert the whole apparatus the soundhole. Once in position, you tilt the retriever carefully, catching one edge of the dowel on the bottom of the case and slowly pulling the post towards you, the friction of the wedge holding the post fast until it's perpendicular to the top and bottom. At that point, a final yank separates the retriever from the post itself, and the system is sonically connected and complete.
If you've done everything correctly, this is what you end up with:
