Body Size

[Phil Jackson]

Any opinion of what is a good body size for a given scale length on a classical guitar?  I know Torres made many different body sizes and scale lengths.  I would like to do something in the 335mm range.

[Donald A. Fortune]

Hi Phil-- I have made a few classical guitars in my time and I have followed a plan to the letter and I also made a classical to my own specs.

I made a dread. size body with a 25.5 scale--

It came out well and boy the sound was gr8 too and talk about loud?? 

I believe you can make a classical any size you want as long as the top is braced correctly.

Just my two cents...

best to you on your indever ( spell check)

Peace, Donald

 

[Phil Jackson]

Thank you Donald - It seems to be a bit more complicated than simple bracing.  My friend made a tiny six-string but someone retuned it to a modified ukulele.  I don't know how they knew!  But it was perfect.  The small body should accentuate the trebles so, I would think the scale length should be shorter.  But that's all I believe.  HELP!  A 650mm scale (27 5/8"+-?) is good for larger guitars but what about something like 630mm or smaller?

Phil

[Ned Knepp]

Hi Phil. 

 I think you mean 25.59 inches for a 650 mm scale length. A 630 mm scale would be a bit more than 24 3/4 inches. Just for the record, 6 string ukulele's have been around for quit a while, you just don't seem them very often. That may be how your friend knew that his small guitar might sound good that way.  I'd guess that it doesn't have a lot of sustain and that tuned as a guitar the bass was lacking. On the other hand, tuned as a 6 string ukulele, the paired strings probably ring pretty well. 

I think the issue of body size is not as tied to scale length as you think.  Look up travel guitars on the Internet and you will find some guitars with pretty small bodies and fairly standard scale lengths. That said, I haven't seen very many people using them for gigs and my opinion is that they don't sound all that good. 

In my experience, small bodied  acoustics almost always have shorter scale lengths. I have an old parlor with a small body, about 11 inches wide on the lower bout, that originally had a scale length a bit under 22 inches. I don't know how it sounded because it was not in playable condition when I got it and I'm changing the scale length a bit. It was probably tuned up a third with that short of a scale like a size 5 martin. If it was tuned it to standard pitch the strings would probably be too floppy. 

In your initial post you mentioned wanting to use a 335 mm (13 inch) scale length. That's a short mandolin or ukulele scale length which would be pretty cramped for adult hands. It's doable but I wouldn't expect it to sound like a guitar since it would be pretty hard to attach a very large body to a neck that short (6.5 inches to the 12th fret). There are ways to gain some extra length by moving the neck/body joint and bridge positions but the scale length is so short it would be hard to gain much. The bridge placement would quickly move well off center on the lower bout and probably negatively effect the sound. The small body probably wouldn't have a lot of sustain or bass but, like your friend's 6 string uke, it still might sound ok in a ukulele way.  

Honestly, if this is the type of instrument you are interested in building, I'd suggest that you look at mandolin and ukulele plans. Maybe talk to your friend and find out if he has plans for his ukulele. You said it sounds good so having ready made plans is a plus if you can get them. The scale you want to use is a pretty short scale ( my soprano ukulele has a 14 inch scale) but it's possible if you want an instrument that small. 

[Phil Jackson]

Thank you Ned,

I guess I made a typo when I said 335mm.  I meant 635mm.  Your knowledge on the subject is vast and quite correct.  I build classical guitars and have found that if the body size is not proportional to the scale length, sometimes the sound of a short scale gets to swimming around in a large body, lacking focus.  But, I would agree that there is no direct connection - just like other things in lutherie.

What is your opinion of the limits of short-scale-to-guitar-sounding-instrument?

[Ned Knepp]

Your words are kind, Phil, particularly in view of that fact that I almost but not quite completely failed to post anything you could apply to your question. :)

You asked about something that I've had to investigate for myself so if my knowledge seems to be "vast" it's because I've found that's it's handy to know. I'm really just a long term hobbyist that has made a lot of mistakes. The first ladder braced guitar that I converted to X brace had to be done twice because I didn't make sure I understood the relationships between brace position, bridge placement and neck length/ scale length. NOW, I have a pretty go idea of how it works.

In thinking about this some more, believe I need to contradict myself and say that shortening a scale length significantly will probably require a smaller body to keep a balanced sound. It would surely be possible to fit a 22 inch scale ( "tres" length) to a dreadnought body but the neck joint and bridge placement would become a big issue, I think. To keep the bridge placement decent a builder would need to move the neck body intersection up the neck a couple of inches. I think the result could be playable but I don't know how desirable it would be plus I don't know how well a short scale would drive the large top.

I've done some experiments with my baritone ukulele which has a 22 something inch scale length. I found that very light gauge steel strings bring a sound that I find more guitar like but the sustain isn't improved much which I attribute to the fairly small body size. I haven't experimented beyond that yet but, right now, I think that it is an indication that what I consider a guitar sound wouldn't survive in a body much smaller than a parlor size guitar which is around 25% more than my uke.  I like the sound of the size 5 Martins and I consider it a true guitar sound even tuned a third higher than standard but I don't think that the properties I want in a guitar sound would survive in body that is much smaller than that. 

At any length, what I consider a guitar sound and what you consider a guitar sound may be different. It could well be that you would find a smaller body completely acceptable.

[Phil Jackson]

Ned,

You and I have more in common than not!  I am a luthier but then all luthiers are hobbyist with their necks on the chopping block.  Like the legendary Jose Ramirez III, I love to experiment to find knowledge.

You said, "Brace position, bridge placement and neck length/scale length."  Setting brace position aside for now, since I only build classicals, we are left with bridge placement and neck/scale length.  Is there an ideal position of the bridge on the soundboard? 

It's hard for me to understand your words since I only build classicals.  It's like we need a translator.  Or maybe not.  And, isn't the body joint always at the 12th or 14th fret?  Do you mean to say that bridge position relates to body size?

[Ned Knepp]

I do not  think there are any concrete "best" on a guitar. I will say that bridge position can effect sound/tone and playability.  "Best" is subject to personal preference. Bridges placed more towards the center of a body sound different than bridges moved closer to the waist. There are too many variables to do more than make vague statements and everyone has a different idea of what works.

I also don't think it's possible to leave out bracing on a classical guitar any more than you could on any other design. Scale length, neck length, bridge position are all related. Bridge placement will effect the bridge plate which is part of the internal bracing. Moving the bridge plate to match a bridge movement will effect bracing. Small changes may be absorbed in the tolerances in the design but a large change in scale length, like 2 or 3 inches in the case of tres guitars in comparison to a "standard" size guitar will cause enough change in the instrument that a rethink of the internal bracing and possibly even the position of the sound hole should be part of the redesign. 

 Joining the body at either the 12th or 14th fret is more about having access to a complete octave on the fingerboard and having room to use it than it is a "must". There have been successful models which joined at the 13th as well. Guitaron's are usually fretless but have very short necks and a bridge moved deep toward the tail block.  It's possible to build just about anything but, in my experience, extremes tend to be pretty specialized in their use. Guitaron's can boom away as a bass but it seems that most bass players prefer something with more range.

 If you are interested in reading more about these relationships, I would suggest that you take a look at Paul Hostetter's page about the evolution from 12th fret to 14th fret guitars here. He was involved in the development of a 13th fret guitar for Sants Cruz Guitars and has some information about that on the site two. In fact he's got a lot of good thing on the site so take a look if you haven't already.

I don't think that bridge position necessarily relates directly to body size so much as I believe that a large change in scale length will probably result in at least a fair shift in bridge position which will effect bracing which may mean that the most efficient use of the string energy my require a different sized body. I think that this is more likely to be the case if the shift is toward a much shorter scale length.  

[Phil Jackson]

OK.  I gotcha.  Good stuff.  Let me chew on it a while.  Thanks!

[Phil Jackson]

Ned,

I read Paul Hostetter's article.  There is a bewildering amount of information with an even more bewildering amount of implication.  But all of his conclusions seem sound, and interesting.

For my purposes, I would try to locate the bridge in the middle of the lower bout (his last example) and keep the 12th fret at the body joint.  Also, let the hole split the 19th fret.  That would practically dictate the body length.  Depth and width I can handle with my experience and common sense.  Then I'll try to remember what worked and try to do it again!

[Ned Knepp]

That makes a lot of sense to me, Phil. I want to experiment with a 13th fret placement some time on a steel string. After reading what Paul wrote and "talking" to him here, I think it my be a very good way to have more room on the neck and keep the bridge closer to centered in the lower bout. I'm also intrigued by the extra depth that Gibson used on the Nick Lucas models which were a smaller body than their jumbos. Everything I've read indicates that there are limits to the amount of gain I could get from deepening the body but it also seems that some added depth can help compensate for lost top area.  

I have a (bad, just ask my wife)  habit of hanging on to the stuff I screw up in my endeavors to make "art" from chunks of wood. One of the things I had laying around was a mandolin top blank that I started carving backwards (really gota remember that everything reverses when you turn the top over) and had to "discard". It laid around for years until a few years ago I came across it and decided to finish carving it into something that might work.  Since my original mistake was carving the scroll on the wrong side I decided to create a small guitar shape which allowed me to use the mistake to form the lower side of the upper bout. It carved out and taps so well that I decided to make a back too.  I made that from a mahogany plank I had because... well because I don't have a lot of faith in my ability to free form an instrument that works and I didn't want to waste my maple. I stopped there because I realized that I really didn't know where this was going but I didn't  want to make another mandolin.

 I've finally decided that I might try fitting a scale length in the range of 20-22 inches but by the time I decided that, I'd lined up too many other projects to start again on this one again. There are so many decisions that need to be made before I do anything else anyway but I think I've worked out how to use it to experiment with the 13th fret placement as well as a deeper than usual body. I also may go with only a side port since the top is small but taps well on the upper bout as well as the lower.   I haven't braced it yet but it will probably be an enlongated  light weight X . The general idea is to keep the top as free to move as possible. At first I though it would be like a baritone ukulele so I automatically though of ukulele strings but my experiments in my real baritone uke and steel strings caused me to rethink that and I now think I should build with steel in mind. Someday I'll get back to it but I have to finish what I have started now first. It's just way to easy to start things.