My Latest Back

[jammy]

Myka - I'm tempted to try the double top thing at some point, I want to get a lot more guitars under my belt first.

I also see where you're coming from about emulating a re-curve with a flat top instrument, and I've seen some makers which do this by strange brace scalloping patterns. A friend in college is currently experimenting with the idea of curved bracing - he's trying to emulate a speaker cone with the top. It looks insane! (I'll get a photo if possible)

I've recently invested in some super accurate scales (when I was in Amsterdam, actually. So I'll let you guess what their primary use is ) but I'm going to weigh the bracing for the top of this guitar, and do some stiffness testing. See what I come up with.

All this talk of bridge weight has me wondering too - another thing to think about!

[Mattia]

If you don't either feather to nothing or inlet the braces, you create a stress riser where the brace ends/butts against the edges. A good whack there, and it can simply pop loose. Inletting and/or feathering eliminates this, which is why I do it.

As for double tops, right now, it seems like a lot of work, and I'd rather maximize the potential I can get out of a good spruce top (which I can get more easily) first

[Myka Guitars]

P.S. Any chance you will find time to make it to the Marylhurst show this year? I am sure you are going to be pretty busy with the move.

I won't actually be in Seattle by then. I plan to take some time and visit some friends on my way across the country. I should be in Boulder during the show this year. Next year for sure. By then I'll have a new acoustic design finished too.

I haven't done anything with the double tops either. I was more curious than anything. It is an interesting idea that is getting some great reviews by builders and players. I can see the merits of a lighter top and how that will increase resonance. The composite nature of the double top will also be much stiffer and open up new ways of bracing that are focused on tone more than structure (always a compromise). I may work with the idea at some point but I agree with Mattia and will get a handle on solid spruce tops first. There is enough to learn there to last a lifetime.

I did start experimenting with a veneered spruce top idea, sort of like this Dragonfly but as a flat top instead. So far it has a good tap tone to it. This guitar idea is a complete hybrid instrument so I am not sure how it would do as a full size acoustic. It is basically a smaller hollowbody electric with a laminated top (burl/spruce/holly) and (in this case) rosewood bracing. It will have a neck pickup and an acoustic style bridge with an undersaddle pickup. It is on hold while I move but I will continue with it in June. Here is what I have so far.

jammy, your friends speaker cone acoustic top sounds wild! Please get some pics if you can.

~David

[fryovanni]

If you don't either feather to nothing or inlet the braces, you create a stress riser where the brace ends/butts against the edges. A good whack there, and it can simply pop loose. Inletting and/or feathering eliminates this, which is why I do it.

As for double tops, right now, it seems like a lot of work, and I'd rather maximize the potential I can get out of a good spruce top (which I can get more easily) first

Hey Mattia I remember reading something about using fillets also to help reduce the stress. Have you ever tried to utalize fillets on inlet braces, or even at other points of brace attachment that form strong angles(I think I recall it being used at the main X also, but I don't recall for sure). It seems like a good idea, but then again may be overkill.

Peace,Rich

[GoodWood]

Ok, say your top is 1.10 Carpathian Spruce, how much would you" feather the edges" for more response? And from what point from the edge? Im thinking 1.5 Inches average, but how much do you knock it down? Kinkead doesnt say.

[Myka Guitars]

Ok, say your top is 1.10 Carpathian Spruce, how much would you" feather the edges" for more response? And from what point from the edge? Im thinking 1.5 Inches average, but how much do you knock it down? Kinkead doesnt say.

The way I do this is to build the guitar full thickness. Once the body is complete then tap from the center out to the edge. You should hear a point where the tapping has less of an effect on the top. This is usually 1.5-2.5 inches from the edge in my experience. As you remove material the active area moves towards the edge. I stop when I bring the active area close to 1 inch. You can go further but it does weaken the edge so keep an eye on it. You can use the binding as a gauge so you don't go too far. To make it easier to take an even amount all the way around I use a sharp block plane set to take a very fine slice. This also requires less sanding to clean up after you are done.

I have heard of using an orbital sander for this but I do not recommend it as you can go way too far with it. If you do use one you may want to try a higher grit so you can go more slowly.

~David

Edited March 13, 2007 by Myka Guitars

[GoodWood]

So your taking off the top?

[Myka Guitars]

So your taking off the top?

To paraphrase your question: Am I removing wood off from the perimeter of the soundboard to feather the edges? Yes, the wood is feathered after the body is completely glued together. This is only way to know how it will affect the response because until the sound box is built it is all speculative. I should also mention that I only treat the perimeter of the lower bout. I don't bother with the upper bout at all as I don't see the need nor do I hear an effect when I tried it (once).

I have to ask that you please be careful and very methodical when doing this procedure. I took a class where I learned this technique and one of the students sanded through his cedar top during this process (another good reason why I use a block plane). Go slow and don't remove more than is necessary for strength. This is a subtle improvement and it is not worth risking the integrity of the soundboard to achieve it.

And to add more to the discussion of bracing check out this approach: I-rib piano bracing.

I also came up with this picture of a similar idea:

Here is the rest of the article.

Interesting stuff.

~David

[jammy]

I beams - what a weird design.

I still have a hard time accepting that removing material in that way actually strengthens the beam! Clever stuff indeed.

I feather the edge of my soundboards in the same way Myka, just on the lower bout too.

[fryovanni]

I beams - what a weird design.

I still have a hard time accepting that removing material in that way actually strengthens the beam! Clever stuff indeed.

I feather the edge of my soundboards in the same way Myka, just on the lower bout too.

Jammy,

It is not so much that removing material adds strength. It is more that given the same amount of material(displace material from the middle of the beam and use that material as added height). The taller beam is going to be stronger, and removing the middle of a beam reduces strength less than is gained by the added height. Thus making it more efficient in this application.

As Mattia mentioned you really have to think about what you are doing and is it really going to improve the performance significantly enough to warrent designing around and or possibly creating a flaw in the structure(if you remove too much or in the wrong location). Really though this is much like scalloping or any other method of carving to optimise the bracing shape to give you as efficient a system as possible.

Peace,Rich