Variations in soundhole to bridge distances

[Dave Bagwill]

If we're talking successful guitar models, not one-offs or anything like that, what is the range of distances between the bottom of the soundhole and the saddle?
What brings this up is an attempt to decide whether to use a 14 fret neck on a 12 fret body. I know the stuff that needs to be changed to accommodate this, but I can't get my hands on specs for that distance. this is an 000 sized instrument.

[Dave Bagwill]

The guitar on the right - a 12 fretter by design - using a 14 fret neck will of course bring the bridge closer to the soundhole.
Things in the box will be changed around, of course, but is there any rule of thumb as to a safe minimum distance between the bridge and the soundhole?

[ken cierp]

The 14th models by design have the bridge plate etc. 1" or so closer to the sound hole than a 12th fret model with the same scale length. So that's a non-issue with your proposal. All you'd need to do is add a few frets to get the FB extension to line up with the hole and look in proportion. For the purpose of conversion -- some would say that you are compromising the "acoustic advantage" of the body that was designed for a 12th fret neck by moving the bridge off the "sweet spot" of the lower bout.

[Dave Bagwill]

Yeah I've read that opinion before and I'm not sure I'm buying it. Mainly because, early on, I've done this once before with very good results; I did not of course use the original bracing layout for the 12 fret.
I do wonder why, if there is a sweet spot, all guitars are not designed to be 12 fretters? I really like them, and was surprised when Ken told me that only one out of - was it 25, or 50? - necks ordered requested a 12. (Correct me if I'm wrong on that, please).

I think of it this way: suppose someone hands you the outline of a guitar, wants that shape, wants a 14 fret neck. So you , who had no idea the shape was designed for 12 frets, make it happen. You think through the bracing etc.
Then again, I'm known for 'rolling my own' and seeing what happens. Not always a success!

My question though is still what the minimum safe distance is between soundhole and bridge.

[John Parchem]

My question though is still what the minimum safe distance is between soundhole and bridge.

I do not understand the question, by safe do you mean structurally safe or acoustically safe? Also do you mean What is the closest I should go to the sound hole or What is the farthest I should be from the sound hole?

A guitars sound is subjective, the sweet spot for a bridge could be anywhere that sounds right to listener. If one defines the sweet spot as where is the best place to transfer the energy of the strings to the lower bout it would be in the center of the lower bout. The movement of the bridge off of that spot for a 14 fret guitar was a compromise for playability. Some of the parameters being tuned were that it still looked like a guitar, maintaining a comfortable scale length and the sound.

The bridge is fixed based on the scale length and the fret that is on the neck body joint. So if you are keeping the same shape the only thing that could move design wise is the sound hole.
You could leave the sound hole it where it is, adjust the bracing and as Ken said bridge ends up an inch or so closer to the sound hole. The guitar will have a different sound than a 12 fret, maybe balanced toward the trebles, but it is a sound that is pretty normal in acoustics guitars. This would be the minimum distance that makes any sense as moving the sound hole closer to the bridge would increase all of the negative 12 to 14 fret conversion issues.

I am doing the same thing on a 00, I used the same shape and I moved the sound hole toward the neck about a half of an inch mostly for looks. But like I said above I had no choice where to place the bridge as it was just a measurement based on the scale length. The 00 design had a short scale, I could have changed to a long scale and pushed the bridge down a bit more toward the center, but the customer, who really just plays for himself, is getting older and has some arthritis so playability was an important factor and I stayed with the short scale.

[Dave Bagwill]

Thanks John.