Scalloping guide for deeper, more resonant sound & warmer bass

[Foughe]

Hi folks,

I've managed to acquire a Ibanez Concord 682 Black Hummingbird seventies Japan copy for a nice price. (This one has the Gibson open book headstock, and is from 1976).

The bridge pins are very close to the edge of the bridge, which seems odd to me but it seems to work very well, so I won't mess with this.

I've got rid of the screws and the adjustable saddle metal thing... I glued two saddles together and shaped it so it fits the wide bridge slot.

With these changes (and a bone nut), the guitar sounds very , very good. Very loud & good volume, good sustain, ... but of course it lacks the overtony thing that rosewood back & sides guitars have.

The only thing i would like to change in the future, is giving it a richer, more complex, deeper sound/tone.

These guitars came with heavy straight bracing (and a big rosewood bridge plate-.
Can anyone give me tips on how to get this more complex, deeper, more resonant sound without compromising the structural integrity of the guitar (i don't want the top to lift anymore behind the bridge).

- How much can i scallop? (only a very little bit?)
- What are the the areas that i should scallop (legs of the x braces, two tone bars, finger tone bars = everything?)? Or only the legs of the x braces? Or only the tone bars or one of them?
- Will shaping them parabolically have this effect too or should i only try the scalloping path?
- What measurement do i have to keep in mind when scalloping (directly from the x or 1" up until ...)

Thanks for your insights!

[hat]

The short answer is mainly the rear part of the X bracing. Go easy with it. Take just a bit off ( maybe 1/16", or less)- string it back up, and play it a while. Make sure the top stays stable and doesn't rotate ( belly) too much. If, after a month or two things still seem solid, and you want to go a little more, then again, just a small bit. Be aware that you could end up with a trainwreck if not done right, or if you get too aggressive shaving the braces.

[LeightonBankes]

you need to get a mirror and look in there, then make a plan. Some guitars (especially lower end ones) have the braces poorly tailed near the sides. If this is the case, you'll want to focus on making the ends of the braces (all)thinner near the perimeter. This will "free up" the top, while still maintaining the overall stiffness of the sound board. Beyond that, I hesitate to make a suggestion without seeing some pics of the braces

[Alan Carruth]

One of the problems with scalloping braces is that you're removing stiffness just where the stress is highest. It's easy to go one shaving too far. It takes a while for this to become evident when you do, and by then it's too late.

You have to understand that wood varies, a lot. A dimension that works fine for one set of bracing on a particular top might be much too stiff on another guitar, and too loose on a third one. You can't say much just from the look of the wood, either. Wood stiffness at a given size does track fairly well with density in softwoods, but unless you've got an X-ray CAT scan of the top it's hard to find out what that is. Anybody giving you a number is making a more or less educated guess. Most of the people who have done this a lot will refuse to do that without the guitar in hand, and they're right.

One rule of thumb that has been advanced by Trevor Gore is that 'good' guitars, ones that he likes the sound of and that are stiff enough to hold up, show about 2 degrees of forward rotation of the bridge when the strings are taken up to pitch from fully slack. You could use that as a guide when shaving the braces, and it might even work. It's at least better than just guessing, although it's hard for me to say how much better. I've never done an aftermarket scalloping job. I've got plenty of trouble without that...

[Foughe]

Originally Posted by LeightonBankes

you need to get a mirror and look in there, then make a plan. Some guitars (especially lower end ones) have the braces poorly tailed near the sides. If this is the case, you'll want to focus on making the ends of the braces (all)thinner near the perimeter. This will "free up" the top, while still maintaining the overall stiffness of the sound board. Beyond that, I hesitate to make a suggestion without seeing some pics of the braces

I made some pictures from the internal top bracing using a mirror...
Can you expand your suggestion on peeking in the inside?

https://imgur.com/a/hCThm

[Foughe]

Originally Posted by Alan Carruth

One rule of thumb that has been advanced by Trevor Gore is that 'good' guitars, ones that he likes the sound of and that are stiff enough to hold up, show about 2 degrees of forward rotation of the bridge when the strings are taken up to pitch from fully slack. You could use that as a guide when shaving the braces, and it might even work. It's at least better than just guessing, although it's hard for me to say how much better.

I never heard about this rule of thumb but it is interesting indeed, thanks a lot!

[mirwa]

Originally Posted by Foughe

Can anyone give me tips on how to get this more complex, deeper, more resonant sound without compromising the structural integrity of the guitar (i don't want the top to lift anymore behind the bridge).

- How much can i scallop? (only a very little bit?)
- What are the the areas that i should scallop (legs of the x braces, two tone bars, finger tone bars = everything?)? Or only the legs of the x braces? Or only the tone bars or one of them?
- Will shaping them parabolically have this effect too or should i only try the scalloping path?
- What measurement do i have to keep in mind when scalloping (directly from the x or 1" up until!

A lot of things I believe people should give a go in guitar building and repairing, this is not one of them, if you do not know what’s required to start with and need to ask questions, then you are just shooting in the dark as they say,almost guaranteed failure and guitar into the nearest bin IMO.

If you had built guitars, scalloped braces, tap tuned tops and so forth, then I would say you possess the possible skill set to then modify fitted braces, but the fact you need to ask means really you possibly shouldn’t do it.

Do yourself a favour and just leave the bracing alone, it is so fraught with danger to the instrument.

Steve

[LeightonBankes]

Originally Posted by Foughe

I made some pictures from the internal top bracing using a mirror...
Can you expand your suggestion on peeking in the inside?

https://imgur.com/a/hCThm

I'll give you my opinion. The "side tone bars" are already pretty small/thin, I wouldn't mess with those. The "bass bars" and "x brace" could stand to lose some bulk. Smart people have told me ( and I subscribe) that brace shaving should only be done behind the bridge Because in front of the bridge (toward the neck) is where you need all the strength against the string tension. In summary, the lower bout area of the x and the "bass bars" is where I would cut weight. I actually have done it, a couple of time. I do it when I am about to change the strings. Go light, then if you feel it needs more, just wait until the next string change (you want to give it some time to "settle" anyway) Also, see my disclaimer in my sig