My first contribution - two dreadnoughts post Ervin class

David Aumann · Post by **David Aumann** » Thu Dec 29, 2011 10:45 am

Late in 2010 I spent a week with Ervin Somogyi at his Oakland workshop doing the guitar voicing class with five other builders. This last year my time has been tied up uke building, but here are two guitars recently started and using some of the know-how from Ervin's course.

First is an American Black Walnut dreadnought with red spruce top. It looks like I've stuck the main X-brace in crookedly, but I did it on purpose! The general idea was to make the top a bit assymmetrical and tighten up the treble side relative to the bass. To this end I put in a couple of assymmetric fan braces. I'm not sure what they'll do; maybe they'll accentuate the cross dipole relative to the long dipole and have some effect on the tone. The bracing is all 6.25 mm (1/4") and I've gone for the parabolic longitudinal shape rather than scalloping.

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The second is an Aussie blackwood/NZ Kauri dreadnaught. It's pretty conventional really, except that I've made the bracing thin and tall (the main X-brace is 5 mm wide and all other braces are 4 mm wide) I did a bit of maths on the strength being proportional to width and to height cubed, so hopefully the bracing's in the right ball park. The only other thing I did was the Dana Bourgeois trick of scalloping the bass X-bar and parabolising (?) the treble X-bar. I've never used Kauri before; I made the top about 2.8 mm thick as a sort of guess.

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Comments welcome. David Aumann, Melbourne, Australia

kiwigeo · Post by **kiwigeo** » Thu Dec 29, 2011 10:49 am

Welcome to the forum David and thanks for putting up the pics of your builds. The bracing in particular I'm sure will generate some discussion.

Cheers Martin

peter.coombe · Post by **peter.coombe** » Thu Dec 29, 2011 11:32 am

I have never been a fan of assymetrical bracing. It just doesn't make sense to me. Contrary to popular opinion, there is no treble side or bass side to a guitar, mandolin, or violin, whatever. The top (and the entire instrument) vibrates as a whole. The "bass" side produces the whole range of frequencies as does the "treble" side. This has been shown from laser interferometry tests, and the Cladni patterns will show it as well. However, that does not mean it is not worth trying and seeing what happens, but I have had more success with symmetrical bracing.

David Aumann · Post by **David Aumann** » Thu Dec 29, 2011 12:32 pm

Yeah, I thought about it a bit before trying the assymmetrical bracing idea. I wasn't perceiving that there was actually a treble side and a bass side to the soundboard; just that if the bracing wasn't regular then there might be more different areas on the soundboard that different frequencies could access. I don't know if that's right - just how I was thinking at the time.

jeffhigh · Post by **jeffhigh** » Thu Dec 29, 2011 12:44 pm

I think that asymetry can help with some of the cross modes where with symetrical response there is phase cancellation between one side and the other, by stiffening one side you can then get a net response rather than equal and opposite cancellation.

Dominic · Post by **Dominic** » Thu Dec 29, 2011 1:03 pm

Yes Pete, as soon as someone says bass side/treble side I smell something …rotten. I don’t mean to disparage you David, its just a straight talking place around here. And this is not to say it can’t work but perhaps not for the reasons outlined. Did you learn this bass side/treble side stuff from Ervin?

However, asymmetry is different and Trevor gives a nice explanation in his book about the Fleta asymmetric bracing pattern and shows what it does to the frequency spectrum where a 3rd peak where the back would be is actually a strong asymmetric cross dipole that gives the Fleta its particular sound. No one would say that a Fleta is not a successful instrument.

In this respect, any X braced SS guitar with the usual angled face braces is asymmetric already and is fully entrenched as a design.

This is one the really good thing about the book, it explains in technical terms what a bracing system does to shape the sound.

Anyway David, I’d be interested to hear your approach to voicing your guitars, what you aim for and what feedback you use.

Cheers
Dom

woodrat · Post by **woodrat** » Thu Dec 29, 2011 1:59 pm

Nice Work There David. I would love to hear what the week with E Somogyi was like. What sort of things did it cover and was it practical or theory or both?
I am a symmetrical bracing man myself too as I never could understand the asymmetry of the Martin x bracing design. Of course that doesn't mean that it doesn't work but I just feel that symmetry is better.
Did you go especially to do the course or did you take it in as part of a holiday?

Cheers

John

Dominic · Post by **Dominic** » Thu Dec 29, 2011 6:43 pm

David Aumann wrote:Yeah, I thought about it a bit before trying the assymmetrical bracing idea. I wasn't perceiving that there was actually a treble side and a bass side to the soundboard; just that if the bracing wasn't regular then there might be more different areas on the soundboard that different frequencies could access. I don't know if that's right - just how I was thinking at the time.

My apologies David, your post beat me before I saw your comment. How did you tie in what you learned from Ervin to this concept. Is thinking outside the box part of the course? You are obviously prepared to take a few risks and try different stuff which is great. To make the most of your experiment you need to work out what you actually done. Be interesting to see spectrographs of the finished guitars when you get there.

Happy building.
Dom

simso · Post by **simso** » Thu Dec 29, 2011 7:21 pm

The bracing has been discussed above, I honestly dont like it. That being said, your work quality looks good. Neat clean not too many messy glue stains, symmetrical build, basically job well done

auscab · Post by **auscab** » Fri Dec 30, 2011 11:34 am

Hi David, thanks for showing your build’s.
I like the look of them and I think it would be interesting doing two at once with differences.
With your Black Walnut build, on the top above the upper transverse brace, it looks like a veneer glued with the grain going the other way, First time I have seen that.

And your Blackwood Kauri build , I like that idea , I did the same for my Build,
[Only one build for me so far] I think my braces were done 7mm wide and the smaller ones 6mm, the top was 2.92 down to 2.5 at the edge, I like it but feel it is possibly overbuilt and it sounds a bit tight. sounds like yours is going in the right direction .
I would be interested to know what you think of yours when it’s finished.

David Aumann · Post by **David Aumann** » Fri Dec 30, 2011 12:28 pm

Hello Rob,

Very observant of you! There IS a veneer above the upper transverse brace. About .5 or .7 mm cross grain. Similarly, there is a cross grain patch around the soundhole, about 2 mm thick. The kauri top is taken from a lower angle and didn't have the cross grain veneer installed when I took it, but it has now. And it also has cross grain kauri around the sound hole.

One thing Ervin emphasised was that the upper cross brace and everything above it shoud be rock solid. So I dispensed with the popsicle brace, or whatever they call it, and put veneer in.

How does the kauri guitar sound compared to spruce? From what I've read, it's similar to bunya pine, and that sounds perfectly fine to me!

Thanks for having a look!

Cheers, David.

auscab · Post by **auscab** » Fri Dec 30, 2011 5:21 pm

Do you glue the veneer to the top flat ,or press it down in a dish so it gets a slight radius?

Kauri compared to Spruce ? I dont think it would be as bright , Thats my guess, the others around here could fill you in better than me on at one.

All I can compare to is a Martin 0021 I have ,which I thik is a cedar top, I will have to put a picture up one day to get a better opinion.

And I payed a 73 Martin D 18 or 28 once, and that blew mine out of the water
incredible bass. and that was on a grotty set of old strings. The top was all over the place too, up behind the bridge and down in front.

David Aumann · Post by **David Aumann** » Fri Dec 30, 2011 8:37 pm

Hi Rob,

The tops of both guitars are built in a 30' radius dish, and the backs in a 15' radius dish. The veneer is pressed into a slight radius with a flexible caul to get even pressure over the whole area, and held in place to dry by 12 or 15 sticks in my go bar deck. I keep the top in the dish and keep the sides in the outer mold and glue by exerting downwards pressure on the sides while they are still in the mold. Nothing spreads out where it shouldn't this way.

I have a 1980 D-35 as my means of comparison.

Cheers, David.

Paul B · Post by **Paul B** » Sat Jan 07, 2012 11:48 am

peter.coombe wrote:I have never been a fan of assymetrical bracing. It just doesn't make sense to me. Contrary to popular opinion, there is no treble side or bass side to a guitar, mandolin, or violin, whatever. The top (and the entire instrument) vibrates as a whole. The "bass" side produces the whole range of frequencies as does the "treble" side. This has been shown from laser interferometry tests, and the Cladni patterns will show it as well. However, that does not mean it is not worth trying and seeing what happens, but I have had more success with symmetrical bracing.

I don't have enough experience with asymmetrical bracing to really have an opinion. But it did occur to me while reading your post; that it would be fairly easy to find out if it does make a difference by simply stringing an asymmetrically braced guitar, left handed. Anyone done this?

Nice work by the way David.

David Aumann · Post by **David Aumann** » Mon Oct 08, 2012 11:18 pm

It may have taken me some time to get around to this, but here are a couple of finished guitars. Actually, I finished them about 8 weeks ago, and it's taken me a while to get the pics up for display. Perhaps I should have put the pics in the Gallery section, but the guitars started off here. so ...

I took them to Beechworth Kelly Country Pick in August and asked a few of the good bluegrass players to play them. Mostly, they liked the walnut/spruce one better than the blackwood/kauri one, because it's got a drier tone more suited to flatpicking. The kauri guitar is louder and warmer sounding which may not suit the bluegrassy players. Also, it's appearance is further from the traditional, unadorned Martin look.

David Aumann · Post by **David Aumann** » Mon Oct 08, 2012 11:29 pm

Here are a few pics of the walnut/spruce guitar:

Cheers, David.

woodrat · Post by **woodrat** » Tue Oct 09, 2012 7:30 am

Lovely Craftsmanship there David....Well Done.

What have you on the go at the moment?

John

kiwigeo · Post by **kiwigeo** » Tue Oct 09, 2012 8:38 am

Nice looking gats David. I particularly like the walnut/spruce instrument....

H3ytm@n · Post by **H3ytm@n** » Tue Oct 09, 2012 12:42 pm

Nice looking guitars Dave.

Out of interest, do they have the same bracing as the in your original post?

Philstix · Post by **Philstix** » Tue Oct 09, 2012 2:48 pm

Both guitars look very nice. Am I right in saying that the back of the walnut guitar is a bookmatched crotch-cut piece? I just finished a tenor ukulele with a crotch-cut walnut top and back, the figure is spectacular. My only concern was the stability of the wood and obviously that would be even more of an issue with the larger pieces in your guitar. So I wonder was that a consideration in your build? I have been told that it could have long term consequences for the finish.

Kim · Post by **Kim** » Tue Oct 09, 2012 10:49 pm

Great work David,

Thanks for joining us at the ANZLF and for being so open with your ideas.

Regardless of bracing patterns your craftsmanship looks excellent. I will only add what you probably already know. What ever you think is the roo's shoes today is likely to change tomorrow..thats the real fun bit of the craft.

Cheers

Kim

David Aumann · Post by **David Aumann** » Tue Oct 09, 2012 11:17 pm

Hello John, Martin, Mike, Phil and Kim,

Thanks for your kind words. Some of you asked a few questions.

John, I haven't been totally slacking off this year. I've built quite a few ukes and I'm almost finished another dreadnought guitar, this time with ziricote back and sides and a bearclaw Sitka top. For bracing I'm using the usual X-brace but with a fine lattice where the tone bars would usually be. The main X-brace is only 5 mm wide and lowest where the braces cross, a la Ervin. I'm adding a photo of that. I've also got a couple of small-bodied guitars under way. One is patterned on a size 2 Martin, spruce top and oak(!) back and sides. The second is patterned after a size 5 Martin in spruce/macassar ebony. I'll add a couple of pics of these too.

Mike, the bracing in these guitars is exactly as shown in the early photos on this thread. This makes it a bit hard to attribute tonal qualities to anythng, really! They're of different woods and with different bracing. What's more, the ziricote guitar, when finished, might be different tonally again. Maybe I should get a bit more systematic and just make one little change at a time ...

Phil, that walnut is American black walnut, and a timber yard near me (Mathews Timber, Vemont) has lots of it. Yes, it's made from a board from the crotch of a tree. It looked pretty so I bought it. The thought of instability DID cross my mind. It's been resawn for a couple of years now and didn't appear to be moving, so I used it mainly on the strength of the figure in it. It has come up quite nicely.

Cheers, David