Sound Post Thoughts

[unclej]

as i stated in my "bridge doctor" post i made and installed one this weekend in a guitar that was really starting to belly or bubble up below the bridge. the bridge doctor worked perfectly for flattening out the top but really didn't bring the strings down much if any at all and i was really hoping that it would.

during this process i came up with a thought that might work or it might just might screw up a guitar. so let me throw this out for your consideration: let's say that you took a deep throated, cam operated guitar clamp and applied it outside of a guitar and behind the bridge. then you apply pressure until it pulls the bridge down to an acceptable height and your string action is now ok. i know you can't pull it down too much without risk of damaging braces, etc. so we're talking relatively minor adjustments that can't be made with a truss rod.

once you got it where you want it let's say that you find a spot, again around the bridge, where you could glue a dowell rod with one side flattened to both an upper and lower brace. once it's dried and cured properly you remove your clamp and you've now got lower action. if you've installed a bridge doctor you could use one side of it to glue the upper portion of your dowell rod to.

now, i have no doubt that mechanically it would work. what i'd like your thoughts on is what would it do to the sound? i did quite a bit of research on sound posts used in violins and cellos and such last night and found that they can definitely enhance volume, change overall tone and repair collapsing tops but their placement is pretty precise. there are several theories on why they work but the one that made the most sense to me was that by transferring the vibrations of the top to the bottom they're now vibrating in unison thus increasing volume.

do you think the same would hold true with a guitar or would it deaden it? have any of you tried it or heard of anyone who has and if so what were the results?

thanks for your input.

[Mattia]

The problem I see here is the direct coupling of top and back; as I understand a bridge doctor, it's on a fairly flexible rod coupling the top to the end block. A soundpost, a la violin, works in bowed isntruments because of the continual (large) amount of energy pumped into the instrument by the bow. On a guitar, I can see it damping the top and the back (they tend to resonate together, although the back's often damped by the player's body; there are some that hold that the back creates a kind of bass reflex couple with the top, acoustically quite different to a violin family instrument, if only because of the kind of energy it receives), and preventing vibration. Particularly if forced into position like you describe, and I'm also not sure it would be able to 'hold' the top down short of screwing both ends of the dowel through the bridge/top and back.

[Setch]

+1

Exactly what Mattia said, no bow = no sustain. Think plucked violin.

Also, the force exerted by a set of medium acoustic strings, will make very short work of a dowel. The forces on a violin top are straight down - parrallel to the bridge. The top of a guitar is pulled in up, not down, and rotated, by the levering action of the bridge, forcing in down in front of the bridge, and creating 'belly' behind the bridge, the dowel won't be under simple compressive load like the sound post of a violin/viola/cello/bass.

[unclej]

The forces on a violin top are straight down - parrallel to the bridge. The top of a guitar is pulled in up, not down, and rotated, by the levering action of the bridge, forcing in down in front of the bridge, and creating 'belly' behind the bridge, the dowel won't be under simple compressive load like the sound post of a violin/viola/cello/bass.

there's a point that i hadn't thought of at all. i'm not convinced yet that it would have a totally detrimental effect on the sound but the contant flexing of a glue joint while stringing and un-stringing the guitar would probably cause it to break fairly quickly. that might just be why nobody's done it before.