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I did a little searching on the forum and found a discussion talking about sound hole size and tone. A larger sound hole brings out the higher frequencies and a smaller brings out more bottom end. Is this right?

But also I was curious about the location of the hole such as sound holes in the upper bout, on the side, as well as their shape. What kind of effects does location and shape have on the tone?

There are several things that goes in to the location of the hole. I am not the one to answer how exactly location will affect tone but the way I locate my hole is in layout of the structure. Meaning fret and scale layout as well as Xbracing layout. Depending on the body dimensions and the bracing pattern you will have a fairly limited location available on a conventional sound hole (on centerline hole). I want my upper transverse braces to be as close as possible to the end of the fretboard with out getting to far past the apex of the upper bout. That pretty much sets my neck side limit. and the splay of the X brace sets the lower side limit. I also want the legs of the Xbrace to be a 1/4" tangent to the sound hole and of course i want the Xbrace to support the wings of the bridge. So for me my bracing pattern, fretboard layout, scale length, bridge location and sound hole location are all designed together as a whole.

Not one thing driving the other but rather all things working together

Jonathan: You are correct about sound hole size. I agree with Michael in that the total top is a system and are very much interconnected.Given that you can increase/decrease the size of the sound hole with a bit of tweaking of other locations and sizes.If you are new to building I would suggest that you get a respected plan and get a few guitars under your belt before doing any design work. If you have built a few guitars please forgive my presumption. Good luck.
Tom.

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A person who has never made a mistake has never made anything!!!

Yeah I'm a rookie at this . I have plans and templates from LMI so I think I'm ok as far as that goes. I was just curious

First: get the 'Big Red Book #1' from the GAL and look up the article on air resonance by William Allen. That will cover the basics pretty well.

If you think about all the guitars you see, what proportion of them with one soundhole have it in some 'weird' position? 1%? 2%? I think there's a reason for this. It seems to me that having the soundhole just north of a pretty nicely pronounced waist helps to introduce a couple of 'extra' air resonances that can help to define the sound of the guitar, particularly in the upper midrange. I'll note that Dreads, which lack a well defined waist, tend to lack these 'added' resonances, and that seems to be part of the 'Dread' sound.

The soundhole size helps determine the pitch and strength of the 'main air' resonance, which has a lot to do with the low range sound. The smaller the hole, the lower the pitch of the 'main air' resonance, and the less amplitude it will have. The drop in pitch makes the guitar sound 'bassier', but the drop in output makes the trebles come out more. So, as usual , there's a balance to be struck here.

Moving a hole of a given size up toward the upper edge drops the pitch of the 'main air' resonance, without changing it's strength. It also starts to sacrifice that other useful interaction I talked about, but, at the same time, might 'listen in' on internal air resonances that are not normally heard. Whether this is a good thing for the tone or not is hard to say.

Changing the soundhole size probably effects other things as well, such as the 'upper cuttoff frequency' of the hole. That's up in the 3000-5000 Hz range, where there are lots of other things going on and it's difficult to sort it all out. It ought to make a difference, though, and what I hear from guitars with different sized holes suggests that it does. I'll make a dangerous generalization and say that a larger soundhole, all else equal, will tend to give a more 'open', but less 'interesting' tone.

Michael

(Sorry, bit of an off topic question - don't mean to hijack)

I have a question about the bracing of the guitar diagram you showed.

How do you carve those braces, scalloped or otherwise.

Thanks
Neil

On my double X bracing I tend to not scallop. They are more or less parabolic in shape. I say more or less because neither the profile nor cross section are true parabolic. Semi-elliptical may be a better term. I taper first the rough shape with a finger plane. I tune the plate with the finger plane by gradually removing mass from the braces and blending the contour into the semi-elliptical shape. That said a good sharp chisel and you can scallop as well as you do any other X brace pattern your valleys will be shorter and in different locations. but scalloping is not the end all and or only way to tune bracing. It is all about adjusting mass in appropriate locations.