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This is an experiment in creating a braceless top supported by a truss system that deals with both structural issues, neck and string pressure. I was able to string this to tension without the top in place. This is my first build, so unfortunately, it will be hard for me to know what issues are affecting the sound. The size and shape are my own design, based on my whim. The back is carved maple. The top is sitka spruce.
The body:
Upper bout 13.5"
Middle: 10
Lower: 16"
Length: 22"
The back is still heavy and I have not done the re curve on the edge. I left the top at .125 to start somewhere. The F holes were carved 15 years ago and are seemingly in the wrong spot. Suggestions on top material and thickness would be welcome. I would like to try some tops with other sound hole patterns. It seems there is a lot of sound in the massive upper bouts that would like to get out.

The longitudinal trusses are .25" down from the top. Then there is an underbridge that is hour glass shaped, there are platforms the size of the top bridge feet, the rest is thinned out. I left this long so I can move it with the bridge to try and find a sweet spot to determine scale length.

The trusses are 1/2" plywood, to start with something. I would like thoughts on materials for this, I would like to try hardwood, softwood, and brass(cut on a water jet).

The underbridge can be any thing as well, right now it is a very hard and heavy wood. Bracing can be added to modify sound, but is not needed to strengthen anything.
If I try this again I will use a standard pattern so there will be some ability to compare the sound.

I strung it up yesterday. The sound is different, the top seems to display characteristics of being heavy, sounds great when you dig in and play loud. The tone is piano-ey but it projects well with great sustain. The tone is warmer with the bridge up at a 25" scale then down at 26". I am not all that familiar with arch top tone, but I think it compares better to that crisper jazz sound. It sounds good tuned down to C. I also have never heard a guitar "open up", so I do not have any idea of how the sound will change.
I would love some thoughts and ideas, I am sure this has been tried before but I have not seen it.
Thanks,
Rob

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Very original, and as such, you are in uncharted territory. I have no advice until you are ready to start on #2.

I will try a few tops on this guitar and will start on the next shortly. I have some money for parts so I would like to buy stuff before the money goes elsewhere. I would like to build another guitar, but it would be interesting to take a belly up guitar with a bad bridge and add the trusses with a new top to see what happens. This guitar is a hack job started 15 years ago and finished last week. I don't want to spend too much time on it, I just want to get a direction for the next one.
Rob

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Boy, I'm a little confused here. If you are moving the bridge back and forth you are changing the scale, and your frets would be off. Tone bars on an arch top instrument theoretically do nothing to keep the top from collapse, but transfer tone. There are a few mandolins being made with no tone bars and seem to work. Not sure what all the interior bracing is for, but aside from keeping the neck block and tail block from rotating, I'm not seeing the purpose. Can you explain your motives a bit more?

Same thing for me... You just CAN'T change a scale lenght like this and say 'Oh it's better at 26'... Frets are displayed in relation with the scale lenght. I just don't understand those kind of bracing? What are they for? Same thing for the underbridge? Just please explain a little bit more.

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Francis Richer, Montréal
Les Guitares F&M Guitars

Haans,
Yes the frets are off, since this is an experiment in bracing and body shape, I used an old fingerboard double stick taped in place. Once I settle on a spot I will call that the scale and install the proper fingerboard. The interior trusses support both the neck and the strings. It is a flat top so it does require support. The support that sits accross the trusses is only as big as the feet of the bridge, and that is all that touches the soundboard on the inside. As for tone bars I think they would help since the sound is lacking in certain elements, namely warmth. I guess on one of my new tops for this I can try some thin tone bars on a thin soundboard. I would love some recommendations. Anything attached to the top is for tone only, not support. I can understand how a carved mando does not need the tone bars, as this guitar is somewhat mando-ish in the very crisp and chunka-chunka chord sound.

Years ago I help Ned Evett replace the fingerboards on guitars with a piece of glass to make a fretless guitar. He still makes and uses them. I ended up with a few extra fiingerboards so I am using one.

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I wish I knew a mathematical way of determining scale length on a 22" guitar with an carved arch back and flat top, but since I don't, I am fishing for a sweet spot. An advantage of using a floating bridge on an experiment.

I will try to explain the trusses more clearly. The trusses are 1/4" under the sound board, the underbridge is a 1/4", if I removed the underbridge the top would crush from the weight of the strings until it hit the trusses. If I used the trusses as bracing they would be two very heavy logs and kill the sound. So the underbrige sits perpendicular to the trusses and is thinned to only contact the top where the floating bridge feet are.

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Can you remove the "underbridge" piece altogether, just temporarily? The bridge would likely press the top down in somewhat, but if it would hold up well enough to bring the strings up to pitch for a short time, just to hear the difference in sound, I think you'd gain a lot of insight from doing that. I'd be willing to bet it would sound radically different.

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I can do that and will, though not today. When I get new material for some other tops I will be glad to test this one potentially to its demise. I will order them tomorrow. I am sure it will be much different. I did move the underbridge back and forth though. So that the underbridge is just in front of or behind the bridge feet. I was not able to pick up any clear changes in tone from this, but I am sure that they were there. As all instruments, I can only hear so much from the players spot and have not had any one else to play it for me so I can hear it from the front.

I would like to make a bridge that has split feet, so four feet all together, the feet would sit on the front and back of the underbridge.

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I guess the other experiment could be to use 2 underbridges with the top bridge in the middle, then I can push the underbridges away from the bridge until I see some flex in the top.

The underbridge is floating and left so I can manipulate it with a violin soundpost tool.

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Robert,
You are asking for suggestions. First of all, I hope you're enjoying your experimentation. However, I think you might want to consider learning the basics before going off on acoustic/structural tangents. A lot of people want to hit the ground 'innovating' rather than earning their bones by doing the work.

Miles learned classical jazz long before he recorded "ich Brew". Segovia painted realistic life studies before "Guernica". And I'll wager that Dr. Frankenstein got a good handle on basic anatomy before he jumped into reanimating the creature.

I don't think that there are any shortcuts to becoming a "master luthier" whatever that may mean. Of course, maybe you're just having fun with this project and don't have dreams of becoming a professional builder. In that case, have a ball. But, if you want to pursue this craft sincerely, I suggest you do the work first. Learn the basics, by building several more 'traditional' guitars (be they x-braced steels, jazz or classicals) Build lighter-see how light you can build before the instrument implodes. Build heavier--see how heavy you can go before it sounds like a six-string brick.

Anyway, good luck with your project-have fun.

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NOTE: Miles Davis didn't record "ich Brew" but apparently the software edits out the term for a female dog. No problem.

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michael propsom
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Excellent comment and I agree with you 100%
Some back story on this project. I think it was 1992, I was living in Miami Beach FL with my girlfriend who was a working student musician playing cello for the New World Symphony. Through her I met the local bow rehair guy, a builder just coming into his own. He was intense. I learned to rehair bows for him and do basic repairs. I got to watch him bust out a violin, and I mean it, he flew and it was perfect. Then he did a cello, and that took more time, that is a lot of wood.
He offered me some wood cheap that he can't use and for some reason I wake up one day and want to build a long guitar with a carved back and flat top, f holes and I want to connect the head and heal block to eliminate top bracing.
He threw me out.
He said he did not want to share secrets, but part of it was this thing that I wanted to make was disrespectful to the tradition of violin making. His feelings echoed yours, and even as a younger person I agreed.
Loosing that job put me back to working as a cook. But I left with a cool carved back and a sound board. I cooked and traveled for 5 years and put together a neck and sides.
Desperate to get out of kitchens I end up renting a store front and got some local work doing rehairs and some basic repair. Right before I starved the neighbor took me in and taught me how to be a glazier. In SF we had all these cool windows that were rotten, and I wanted to make new ones.
So again reaching past my skill level I started making windows and doors. Eventually becoming skilled in cutting curved window and parts of all sorts. I had my shop there for about 8 years when I was ready to down size from the madness of payroll and city life and move to the magnificent town of Mount Shasta. I have continued as a woodworker, doing whatever, from cabinets to tables, bars and of course the Affordable View window frame. Of which I am bored, so I wake up and say I am gonna finish that @#$% guitar.
And all the stuff that was hard back then is much easier now. Why? paid some dues to woodworking craft living in the cold coastal woodshop for 8 years making jigs and setups and tool choices.
The lesson. If you make something 10 times, the 10th will always look better then the first. Just like playing a song on the guitar.
So I don't know about becoming a guitar maker, but I do know that for last 2 weeks that I have been finishing this I have found a renewed excitement for my shop. Fortunately my wife is earning the dough and I am raising the daughter, so I get 2 hour windows to work a bit. I know that this will only be for a little while longer, and in that time I would like to make some more odd guitars.
So after 17 years, I have finished this THING that I have hacked and hauled with me for years. WooooHoooo.
My next try will be a standard parlor shape, but yes, the truss system will be there too. I may try an LMI kit so it can look more like build #10 and less like #1.
Thank you so much for the words of wisdom, making instruments out of wood is truly the highest form of woodcraft, I have tremendous respect for any who is truly skilled and educated in their individual craft to the high degree of the builders in this forum.
Rob
Didn't start this post planning on writing a biography.

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I just pulled the underbridge back from under the top bridge to create a gap of about 5mm. I notice a slight belly occur on the bottom, but the sound is dramatically different.

I don't want this one to break until I have stuff to fix it. But when I can, I will continue to pull the underbridge down to note the changes.

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So I'm confused, doesn't the downward force of the strings on the bridge sandwich the top down against that piece setting on top of the trusses? It seems to me this would pretty well damp most of the vibrations, creating a quiet and shallow sounding guitar.
Help me out here on how it's suppose to work.

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That is how it works, though the guitar has decent volume, it is a lack of warmth that I don't like at this point. Offsetting the underbridge from the top bridge does warm up and improve the sound considerably

You are right with the challenge of making this a good tone transfer system, can I get the vibration from the bridge into the soundboard without the truss system killing it. Minimizing the contact area between the underbridge and the top seems critical. I went with the 1/2 plywood trusses thinking if anything will kill the sound, this would, if the sound survived somewhat, then I will call it worth my time to make some thinner trusses. At this point I will try thinner trusses as I feel the sound is close but different then my 2 production dreads. Any suggestions for material? I have a port orford stash, but nothing with the grain going the way I want. I may be able to get some locally. Or I can try to make my own hardwood 3 ply, maybe as thin as 1/4". Carbon fiber could be cool, or perhaps very thin wood with fiberglass.

I doubt I am heading towards the holy grail of guitar tone, but the system does seem have some potential.

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Bingo. I don't think you're confused Jim! Comfyfoot, in very simplified terms the main mechanism by which a guitar makes sound is that the bridge levers the pull of the strings to a direction perpendicular to the plane of the top, driving the top up and down like a speaker cone in sympathy with the strings' vibrations. This leveraged energy is not much as forces go, hence the compliance or flexibility of the top/bracing system is paramount. Generally one strives for the most compliance possible without anything being destroyed or grossly distorted. The result of centuries of this striving are the bracing systems one sees today - sensitive, cunning compromises between strength and compliance. In your construction, the downward forces of the bridge are coupled directly onto the trusses. The fact of those trusses being spaced away from the top instead of glued onto it is making no difference in this respect. It is therefore the compliance or flexibility of these trusses that will mostly determine the output of your instrument. They appear to be exceptionally rigid compared to anything that normally moves in response to string vibration. You mentioned that you were "able to string this to tension without the top in place". How different does it sound with no top at all?

Your system would seem to effectively address "neck folding" problems, i.e., the trusses look to act as a huge extended neck block that carries the rigidity of the neck all the way to the tail. Trapping the top onto this rigid structure, however, immobilizes it. In order for the top to vibrate effectively, its needs should be addressed separately.

I really don't mean to flame or put down here, but what I see is a conflating of requirements for a good guitar. All IMH, know-nothing opinion, of course.

Peace,
Sanaka

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...imagine there were no hypothetical situations...

Didn't realize it was a flat top...good luck!

Look around the forum for zero downforce bridges, there was a thread here a few weeks or months ago. So long as you've got that under bridge pad there you'll be eliminating the monopole mode which is at the fundamental. It's hard to get any decent bass without it.

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Totallly hypothetical as this is a guess rather than a coment based on experience or physics/acoustic engineering. Firstly, I admire the bravery to try something new, I have always believed that there are TWO ways to innovate... the first being one that yields a higher percentage of positive results - thats based on small consecutive trials based on experience with established principles , and i guess mopst on here would advocate that approache, the other is the steaming headlong into something different - the blind invention where teh hit rate is going to be very low, but the challenge and journey can be personally rewarding even if the results are perhaps not as expected.... anyway my point based on a hunch (because I love this approach) would be to drop the idea of a flat top and go with a stressed arch - not a carved arch but an approach some makers are using on backs. This way you would elevate the the top away from the trusses and this avoid the 'compression sandwich' which WILL ngatively effect the natural vibration of teh top you are trying to enhase by making it brace free... I would then perhaps go with a Babich style anchoring of the strings so that the strings themselves also help to maintain the arch?

Just a though,. no idea if it would work, but its a great story and from a personal perspective I admire your bravery!

They appear to be exceptionally rigid compared to anything that normally moves in response to string vibration. You mentioned that you were "able to string this to tension without the top in place". How different does it sound with no top at all?

Y

I really don't mean to flame or put down here, but what I see is a conflating of requirements for a good guitar. All IMH, know-nothing opinion, of course.

Peace,
Sanaka[/quote]
Thank you for the visualization, that is very helpful. I have had this idea for some time, and it is more fun to talk about why it won't work with a prototype then just in theory. I appreciate the explanation.
It sounds like a through neck semi hollow Gibson ES strung without the top. With the top it still sounds like a semi hollow but at the volume of a regular guitar.

As far as the rigidity of the trusses, I wanted to start flushing this out quick and dirty, and I really did not want anything to break on the first try, just stringing this up and and playing it is a personal milestone, even if it is a tone only a father could love.
Rob

So at least I need to compare the weight of my trusses to that of the bracing on a standard top and see how close I can get.

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Sound clip of the guitar with a bit from my Blueridge dread to have a reference. As a said, a tone only a father could love, but it does have its own unique voice, I wonder how it would compare to a Gretch hollow body. Seems somewhat similar.

http://www.youtube.com/watch?v=n2AQaZ6yios

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Another sound clip showing the difference moving the underbridge makes.
http://www.youtube.com/watch?v=0rLPX4tacwA

A heartfelt thank you to all who have chimed in to offer insight to this. I will continue to educate myself on the dynamics of downward pressure and sound. Thanks all for the references, and please continue if any one has any thoughts of a top that I should try, I would like to try the stressed arch idea.

To move forward I will try a few tops with some different combos of light bracing and using the underbridge, as well as some more standard bracing. Hopefully in the end this can be a playable guitar for me however it ends up being braced, meaning comparable or better then my current guitars.

I will post the next version when it is ready.

Thank you again.
Rob

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Rob,

As you know the scale length and fret location is a mathematical formula that is critical to the instrument playing in tune. In your case, it is the fret board was already slotted and that will determine your string length. Measure the distance from the nut to the 12th fret. This is half your string length. Use the same measured distance from the 12th fret to the saddle of the bridge. As long as the fret slots were cut correctly for the string length they were designed for you should be close on intonation. You will need to add a small amount to the length in order to compensate for bending the string when depressing the string. Easiest way in your case is to use the above as a guideline to start. Pluck an open string and then pluck depressing the 12th fret. Move the saddle slightly away from the nut until the open note and the 12th fretted note are at the same pitch. This should give you pretty good intonation up and down the fret board.

Regards,

Philip

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If you think my playing is bad you should hear me sing!
Practice breeds confidence and confidence breeds competence. Unfortunately, I'm stuck in practice.

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