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Hi all.

Chances are I'm going to have to build an OM/12 fretter for a customer. I've never done that before, although I know nothing is tricky here, I just need to make sure the bracing patern is shifted accordingly. But I'm wondering about the soundhole. Should I leave it as a standard OM 14 fretter or shift it as well? What is usually done? And if both are done, what is the differences in sound?

Thanks!

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Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

Alain,

I think there was a lot of that subject discussed in this thread entitled: OM vrs. OOO

Link might work:

http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=16458&hilit=

I know, I read it but it doesn't mention soundhole placement. I didn't want to highjack the thread so I made a new one...

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Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

A OM 12 fretter would be the Norman Blake model. Unless your thinking of a OOO 12 fretter which is a different body shape.

The soundhole can go wherever you like. Usually, they just go near the end of the fretboard so that the fretboard covers the ends of the rosette. I prefer to have a little bit of the top showing at the end of the fb, others do it differently. Decide on a size, then measure from where you want the edge of it to be with respect to the fb, then take the radius down from there, and that's your center.

If you're building it with a true OM body, the flattened one that's usually a 14-fret, go to the Martin web site and find the Norman Blake 000 18 or 28. There's detail photos that will give you an idea as to how many frets, where the sh goes, etc., the way Martin does it. Probly works pretty good.

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now known around here as Pat Foster
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http://www.patfosterguitars.com

Todd wrote in the thread that I mentioned above, "The location of the 20th fret moves toward the body join by .06" for the short scale guitar, so I'd move the soundhole forward (toward the body/neck join) by 1/16", or just make the section of fretboard beyond the 20th fret a 1/16" shorter."

Thanks Steve.

Although that's not exactly what I was looking for (unless I misunderstood what Todd meant); this quote compares long scale vs short scale while I'm comparing 12 fretter ve 14 fretter. The shifting down is more than 1/16".

Answers mentioning the Norman Blake model helped me. It seems I can keep the soundhole position as a normal 14 fretter.

Thanks all!

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Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

Here's a thread from last year that might be helpful too.

viewtopic.php?f=10102&t=11493&hilit=blake

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now known around here as Pat Foster
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http://www.patfosterguitars.com

Thanks Todd and Burbank.

Very precise answers! Couldn't ask for anything better.

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Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

If you use the 14-fret body shape, and a 'normal' scale length, the hole must be shifted down toward the waist to preserve the proper number of frets. This will raise the 'main air' resonant pitch a little, so you might want to make the hole a bit smaller, say 1/8" or so.

The OM was originally a variant of the 12-fret 000, with a longer upper bout. simply lengthening the body eliminates a lot of those little issues.

I have a Larrivee "Pete Anderson" signature model which is a 12-fret OM, 25.4 scale. I measured it just now, the soundhole is a diameter of 3-15/16" and it measures right on 4" from center of 12th fret to the edge of the soundhole. Hope that helps.

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Jonathan Kendall, Siloam Springs AR

In my ever so humble opinion the real issue to worry with is not the sound hole location, but rather the change of position of the X brace intersection and splay angle as driven by the scale length. Let’s say you use a 12 fret with 24.9 scale neck. The bridge and X brace will be shifted rearward as compared to the X brace and bridge location of a 25.4 scale 14 fret neck on the same body by about .88” if I remember correctly. So if you maintain the sound hole in relationship to the intersection of the X brace the sound hole will also move .88”. Now, the sound hole could be theoretically forward shifted with few issues but the X brace position, splay angle and it’s need to support the bridge wings is the design issue to deal with first.