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Plenty of guitars have been built with asymmetric X-brace carves (one scalloped, one not; I believe Dana Bourgeois started it all), and there are a number of guitars out there with a half cedar, half spruce top. For my hands-down favourite, most insane and amibitious guitar done like this, google 'dovetail madness'. First link.

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what would happen theoretically if you used two different types of wood for the soundboard, something trebbly for the trebble side and err..bassy for the bass side

Actually when I took my class from Harry Fleishman this was the obvious next step in his line of thinking and he had already been doing this for years. The dovetail soundboard is one of Harry's signature details. Here is one of his fretless basses:

FILE-7.JPG

And here are a couple more guitars:

Fleishman harp guitar

Fleishman 'Morning Glory' guitar

The results are just what you would expect actually. Harry's research and design always follow his years of experience. I think he uses Redwood and Spruce most of the time.

Man, Klepper's work is just amazing to look at. His level of detail is mind boggling.

~David

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Wow, I have had NO clue.

It looks like the designs are very unique. The body, bridge, assuming bracing system, sound holes as well as top material. Myka/ Mattia help me understand more about the designs. I would never think using two different soundboard materials on a more traditional design would have such a significant impact ( I figured it would be different, but not huge), but it seems like my thinking is way off.

Peace,Rich

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I thought that one of the sides may act as a damper for the more resonant side. However, I think tonal response and vibrations of the soundboard are a bit like aerodynamics, the more you look into it, the more you realise that you'll never fully understand it and it's all a bit weird.

Still, one day when I've got time, I'll make one and have a play. Bamboo and Mahogany maybe.

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The idea of using two different materials for the different sides of the soundboard is somewhat along the same line of thinking as the split bridges that Steve Klein and others of the Kasha style use. While most of the asymmetry is under the hood using something like redwood for the bass side makes a certain amount of sense. It is less dense and more flexible than spruce and if used properly it can deliver a louder and more organic bass. The stiffer spruce side is coupled to the treble strings which resonant more closely in that range and will likely shimmer like glass as is characteristic of sitka. Certainly the overall tone of the high strings is colored by the bass side of the soundboard somewhat and vice-versa but the bracing underneath can be designed to direct the vibrations from the bridge to the particular areas of the soundboard.

The tonal descriptions are generalizations of course but you get the idea. It is a great area for experimentation. One I hope to get into again soon. I really have to build another acoustic soon before I go crazy with all these electric orders I have lately! Not that I am complaining but acoustics are incredibly rewarding to build.

~David

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The idea of using two different materials for the different sides of the soundboard is somewhat along the same line of thinking as the split bridges that Steve Klein and others of the Kasha style use. While most of the asymmetry is under the hood using something like redwood for the bass side makes a certain amount of sense. It is less dense and more flexible than spruce and if used properly it can deliver a louder and more organic bass. The stiffer spruce side is coupled to the treble strings which resonant more closely in that range and will likely shimmer like glass as is characteristic of sitka. Certainly the overall tone of the high strings is colored by the bass side of the soundboard somewhat and vice-versa but the bracing underneath can be designed to direct the vibrations from the bridge to the particular areas of the soundboard.

The tonal descriptions are generalizations of course but you get the idea. It is a great area for experimentation. One I hope to get into again soon. I really have to build another acoustic soon before I go crazy with all these electric orders I have lately! Not that I am complaining but acoustics are incredibly rewarding to build.

~David

Ok that kinda is making sense (I have not researched the Kasha style in any great depth). The idea seems pretty sensable. Bass/ Treble seperation on a single sound board from a common bridge has always been a bit of a mystery to me. I guess I should say understanding how to refine/design and optimize for such. I guess that is why I like acoustics so much. They are way over my head, but really fun to build.

One thought that does come to mind. Does the use of two very different materials Top and bracing seem to have some dampening effect on each other. Maybe a grossly exagerated image would be a speaker cone that is half aluminum and half paper (not a metal dome, but half the cone itself). Seems like it would be oddly balanced and lose efficiency. I guess that could be braced to smooth out the transition and allow them to work better as a unit. I better just do some research. The guys designing these guitars know what they are doing. I just need to learn more about how they are doing it.

Thanks, :D

Rich

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Rich, there is some research that has been done with laminated soundboards. I recall a graphite/spruce/graphite composite guitar (I can't remember who built it) and I also remember a German classical builder who used balsa wood braces (in a lattice) on spruce which was covered in a tight fitting layer of carbon fiber. If you used cork you would certainly get some dampening qualities but the use of a tonally viable material woudl be a better choice. Extreme example I know but you know what I mean. Of course these builders know what they are doing but someone tried it first. Experimentation is always a good idea if you have the time to do it. Keep us posted!

ToneMonkey, no problem. I can take a look in strictest confidentiality and let you know what I think.

~David

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Nice one David. There was another idea but I think it's been done now :D

There was a company set up at Loughborough University making composite guitars. I think they do finate element analysis on it to model the vibrations. I may get in contact and se if they can model something with different top material. I went to that uni so maybe they'll do a favour :D

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Rich, there is some research that has been done with laminated soundboards. I recall a graphite/spruce/graphite composite guitar (I can't remember who built it) and I also remember a German classical builder who used balsa wood braces (in a lattice) on spruce which was covered in a tight fitting layer of carbon fiber. If you used cork you would certainly get some dampening qualities but the use of a tonally viable material woudl be a better choice. Extreme example I know but you know what I mean. Of course these builders know what they are doing but someone tried it first. Experimentation is always a good idea if you have the time to do it. Keep us posted!

ToneMonkey, no problem. I can take a look in strictest confidentiality and let you know what I think.

~David

A lot of folks, particularly in the classical field but also in the steelstring field (including Charles Fox, I think); most seem to be Nomex core (a honeycomb material) with thin spruce or western red cedar skins. I believe Smallman may be the one using balsa braces capped with carbon fiber (not sure, though), and Bill Cumipano's built a guitar with no braces, just a solid CF top. But that was years ago already. Lots of discussions out there.

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  • 2 months later...

OK...after the annual 2-month immersion as a fanatical summer swim team parent (a lot of fun really), I managed to make some progress in August.

I modified the Fox-style side bender so that I don't need a separate one for cutaways. The upper bout has a block that is removable, so that I can plug in a piece of form for a normal bass-side shoulder, a venetian cutaway, or a florentine cutaway. I also exaggerated the waist to make it more incut like a Taylor, and milled out a shim to put in the form's waist if I want to bend regular D sides.

Calibrated the temperature settings for the LMII heating blankets (I'm using two), and cut & planed some walnut sides for practice. I also trimmed a bit off the sides as binding, bent together with the sides.

Here's the treble side, went with the venetian cutaway for this test. It bent quite well, with no horrible cracking sounds or anything. The Taylor-to-D shim is underneath the PVC caul at the waist.

bender2.jpg

I just spritzed the sides with water, laid them into the already-warmed-up bending sandwich (blanket-steel-wood-steel-blanket), and let 'er rip. I did the waist first, then the lower bout, then the cutaway last.

Edited by erikbojerik
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The result? Well....I'd bent the sides at a temperature around 250F, and then after they were clamped in place, I heated it up to ~300F for 5 minutes, then shut it off to cool for an hour. As you can see....scorch city. I guess I overshot the temperature. That'll buff out, eh?

sides.jpg

I will probably not heat the rosewood sides further after bending them. This walnut contraption will become a 4-string acoustic bass.

When I started this proj, my intention was to just put in a single layer of tortiseshell binding. But once I missed the deadline, I got ambitous and decided to use up some of this scrap lumber lying around, and make my own wood binding.

So the purfling will be 3-layer B-W-B using Mac ebony and maple (top, sides and back), and the bindings themselves are just rosewood strips trimmed off the side stock.

Half the bindings are glued up with CA, the other half with Titebond. I'll see which holds up better in the bender.

Edited by erikbojerik
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OK now...THAT'S annoying! 6 posts crammed into 1? :D What's up with that?

Since you don't have flood control, the board merge your posts because they are too close together "time wise".

This is what happens when you try to by-pass the 1 pic per post rule by posting many posts with one pic back to back!!! :D

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Erik,

Looks like the temp. got pretty high. How did you confirm you were running 300-ish? I run between 250-300, but have never scorched. Also do you seal the metal and wood sandwich? I do this to keep the moisture locked in (this may even the temp out a bit, and help to avoid the hot spots). Also did you get a lot of spring back on your cutwway(kinda looks that way in the pic)? Seems like it should have taken and held well at that temp. Also just out of curiosity... How thick were the sides when you bent them? This is a shot of the cut I am working on at the moment (it's sides were at .082", and better full size pics are posted in the group build topic in my build page).

th_DSCF0398.JPG

I have never been able to glue binding and then bend it (heat cooks the glue). I usually bend my thicker binding. The fine line binding (thinner <.05" total thickness of lams) bends easyier and I generally work it by hand in the tighter radiused areas. If you find a glue that will take the heat let me know. It would be nice to be able to one shot it.

That bending form sure looks elegant :D . I figure I am going to have to step up to a heat blanket rig one of these days, and get rid of my heat lamp clunker.

Peace,Rich

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Rich, I have a thermocouple and voltmeter that converts the TC current into temperature. But I suspect the calibration is suspect.

What do you mean by "seal the sandwich"? Wrap it in foil or something? I suppose some moisture may have escaped out the sides.

I had heard that ebony doesn't bend well without heat & steam, so this will by my attempt to pre-bend it. But yeah, I half expect to have it all come apart when I open it up.

There's a little springback but its really hard to tell where its coming from. The cutaway fits the form pretty well. The sides are 0.085".

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Rich, I have a thermocouple and voltmeter that converts the TC current into temperature. But I suspect the calibration is suspect.

What do you mean by "seal the sandwich"? Wrap it in foil or something? I suppose some moisture may have escaped out the sides.

I had heard that ebony doesn't bend well without heat & steam, so this will by my attempt to pre-bend it. But yeah, I half expect to have it all come apart when I open it up.

There's a little springback but its really hard to tell where its coming from. The cutaway fits the form pretty well. The sides are 0.085".

I suppose it is tricky to dial in the temp especially when you are bound to have areas that will insulate or trap heat a bit more than others.

"seal the sandwich" is pretty much just that. I seal the sides of the metal sheets that the wood is placed between. I use a bit of foil and some masking tape (blue stuff). It will not keep a perfect seal (I actually want to hear the sizzle and see a bit of steam telling me it is up to temp), but it does seem to help keep enough moisture trapped to promote good even heating.

Ebony is brittle. It bends pretty well at the right temp. A heat gun or pipe will do the trick for thin binding (doesn't need much moisture because it is thin). If I use .06" or thicker binding it gets bent in the side bending machine with a bit of moisture added (like sides), but I dont laminate any fine line binding to the thicker piece (I bend it by itself). I will be curious to see if the glue you use holds up. It would be easier to bend it all with the side bender in one shot.

That thickness sounds pretty much like were I am at most of the time. If the sides fit the form then you must be in good shape. I find I have to give the cuts and bouts a bit of extra heat to make sure the bends take and hold their shape. With your system you have even heat from blankets though so you wouldn't have to worry about that (again upside to your bender and downside to my bender).

Peace,Rich

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  • 1 month later...

Right...back to this one.

Yes Rich, the bindings came out great! I'm using two LMI blankets with 0.005 spring steel between them and the wood. At 250-260°F the rosewood sides bent nicely, as did the bindings. I tapered the sides first, secured the bindings to the edges of the sides with painters tape (on the edge that they will go on), spritzed everything with H2O from a Windex bottle, let the water soak for a few minutes, slapped it together into the pre-heated blankets (making sure the non-tapered edge was straight) and bent away. Took maybe 5-10 minutes to get the sides bent and clamps in place, then I shut the power off right away and let it cool to room temp (about an hour).

There's some springback in the sides, but I'm building in a mold so I'm fine with it. The bindings came out great, both the CA and Titebond versions. The walnut in the bindings still scorched very slightly in a few spots, but not the maple or rosewood.

I goofed on the neck, so decided to make a new neck blank from the 100-year-old walnut stash, a nice dark piece with some flame. Stacked the heel, did Setch's scarf method within the headstock, glued on the ears and trued up the fretboard surface.

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