Official Luthiers Forum!

Hello all,

I am currently in the process of building an acousic guitar. It isn't the average dreadnought, which is why I have come to this forum for some help.

The body is shaped like a flying V, such as the guitar in this photograph:


I'm having trouble trying to figure out how tone bars should fit into the body, and how they should be shaped to fit the style of this guitar. Any suggestions?

It has come to my attention that since there isn't much of a surface on the top, bracing might not be needed. If bracing isn't needed, should the tone bars go in that area of the back of the face? If bracing is needed, is there a way that tone bars could fit?

Also, once I figure out how tone bars are going to fit on the back of the face, how should they be shaped? Is there a theory behind how tone bars are shaped?

All comments are welcome.

Welcome to THE forum, Jon. I find your idea very interesting and would like to see what kind of result you get. My only observation about this design is that in an acoustic guitar, the sound is created mostly by the vibration of the top plate. I cannot see how this design will allow enough vibration to have any volume. Maybe an acoustic with pickups, more like a hollow body electric. That might give a neat sound.

Ron

_________________
OLD MAN formerly (and formally) known as:

Ron Wisdom

Somewhere in the middle of Arkansas......

Hi John, Eillie Erickson (she hangs out on MIMF a lot) has built some acoustic "flying Weisenborn" guitars that have sort of a flying V body, but they are meant to be played as lap steels. She also wrote an article about it in "Guitarmaker" a while ago that might be helpful for you. I think she uses an x-brace for those tops. To your question: "Is there a theory behind how tone bars are shaped?" the answer is yes . It is a very broad question; you should read up on it a bit and ask more specifically.

_________________
Rian Gitar og Mandolin

Arnt, I'd argue the answer to 'is there a theory behind how tone bars are shaped' is a resounding NO. There are, in fact, countless different, often contradictory theories on how and why tone bars are shaped in a certain way

My gut instincts tell me you will need some sort of bracing, and that I'm very unsure of how 'guitar-like' an acoustic with a flying-V body shape will sound.

There are a _lot_ of theories about how tone bars and braces should be shaped. Most of them are junk, except mine, of course.... ;)

I, too, wonder how 'guitarlike' a flying V acoustic will sound. Ferrington (spelling?) made one, didn't he? What did that sound like?

Jon,

Were I to brace such a soundbox, I would use an X brace that crosses under the lower pickup area, and whose legs go all the way down the arms of the inverted V shape. If you add a tone bar (one may not be necessary, given the strength the crotch of the V would give just below the bridge) it could be below the anchor of the bridge, with the ends close to zero height where they butt against the X, and about 1/2 inch or less high in the center. You might also add a finger, or side brace on the outside of the X's legs, butting up against the X under the fulcrum of the bridge. Again, parabolic, and zero height at each end, as were Martin side braces in the "golden era".

For a picture of some parabolic braces, visit the "Bio and Brace Talk" page of my web site, vanlingeguitars.com.

I feel this will give the soundbox structural integrity and allow for the most sound production, which still won't be much. Have fun.

Scott




Scott van Linge38733.41125

Scott,

Should all of the bracing be parabolic? I've been looking at Dreadnoughts lately, and many of them have scalloped braces. Does this affect the sound of the instrument?

Thanks for your help.

_Everything_ effects the sound.

'Scalloped' bracing is less stiff and heavy in the middle of the top and a bit stiffer toward the edges owing to the 'peaks'. This tends to drop the pitch of the lowest resonant mode of the top, which is the one that produces the most sound, and raise the pitches of the next few modes. The tone tends to be 'full', 'punchy', 'bassy', 'responsive' and to have short sustain. Bluegrass guys _love_ scalloped bracing.

The opposite bracing style, often called 'tapered', has braces that are tall at the bridge location, and get lower as they get closer to the edge. This has the opposite effect on the way the top vibrates, and changes the tone. You tend to get more sustain, more treble, and a 'sweet' but 'carrying' tone. Fingerstyle players tend to go for some form of tapered bracing.

'Straight' bracing, that is more or less the same height all along except at the ends, is what you find on most factory guitars. It tends to sound 'neutral', favoring neither highs nor lows particularly. When well done it can yeild a nice 'all around' instrument.

'Parabolic' bracing is a variant of 'tapered', IMO, falling somewhere between 'straight' and more radiaclly 'tapered'.

Any style of bracing can yeild a very fine guitar if it's done right, but they will all tend to sound different. Different people like different sounds: Julian Bream and Doc Watson might not want to even touch each other's guitars, but they both play very good guitars, and play them well.

There's also the whole matter of the body size and shape, and the wood that's used as well. Everything will change the sound, and you have to get into the habit of looking at the whole package rather than singling out one specific feature as 'the one true way'.   

Thank you Mr Carruth,

This topic makes me want to try and experiment on each kind of bracing, i've only played and owned modest factory dreadnaughts since i was 14 years old. The only great dreadnaughts i tried was one at Mario Proulx and a Martin dc 16re Aura at Steve Music here in Ottawa. And it' so amazing to discover such a wide world of variety and knowledge after so many years in the dark. i thought for long time that i knew guitars, boy was i wrong. I just feel humbled by being here and reading all of this.

If lutherie is a road, i just hope it never ends !

I love you people!

This is the work that I have accomplished so far on the project. As you might notice, I have picked mahogany for the back, sides, and neck. The top wood that I am using is Sitka spruce. The mahogany and spruce are both bookmatched, if not noticable in the picture.

Are there any more suggestions on tone bar placement?

Thanks for your help!

You're gonna have to post a sound clip of this baby when she's ripe. I can't imagine what it's going to sound like.

Ron

_________________
OLD MAN formerly (and formally) known as:

Ron Wisdom

Somewhere in the middle of Arkansas......

Jon,

I would favor tapered/slightly curved bracing for the X, with the tallest at the crossing of the X, and with this size, about 1/2 inch high, 5/16" wide. I'd also make those back braces parabolic, down to under 1/8" where they meet the sides, and curved in cross section.     

Scott

The inside of the legs of the V seem to be in almost the same position as the lower X in a more traditional guitar. I wouldn't bother with an X brace. Perhaps you can make an X using the V as the bottom half. In a traditional guitar, most of the sound comes from the area between the lower X braces. In your design, you have removed that portion completely. Many builders spend a lot of time tuning their tops by shaving the tone bar which are located in the area that you have removed. I'm not saying that this insturment isn't going to work. It's more like it's so completely outside of what we've all been doing that there is no guessing how it will sound.

There are almost no structural loads on the top in the V poriton and I wouldn't brace it there at all. I would put a light 1/4"x1/4" brace right below the sound hole and a stronger transverse brace right above the sound hole.


A potential problem with this pattern is that the bridge is directly on top of the X. It might require a lot of string movement to the any top movement. Perhaps this second pattern might work better.

In this design the corners of the bridge just nick the brace as it does in a more conventional guitar. The major area of sound generation would be above the bridge and down both of the V's.

Good luck.

Mike's right: with the bridge so close to the 'lower edge' the big problem you're going to have is getting some motion there. You coule make the top very thin with no real structural probem in back of the bridge.

How about a pair of braces that run up the middle of the two arms of the V and cross in front of the bridge? Make them very light below the bridge, and larger, say about 1/2" high or a bit less, where they cross. They'd come up on either side os the soundhole, ad you could put a transverse bar up top.