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I’m looking to use a figured Myrtle for a top on a mid-size flat top design.
Are there any special considerations in coaxing the best responsiveness or tone out of a figured tonewood top that differ from the approach with Spruce?
Special bracing?
Maybe those who have worked with an all Koa build could shed some light?
Thanks!

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Wade
Nashua, NH
http://www.wadefx.com

I don't know why in the world you would want to use a hard wood on top for a sound board because in my experience with koa they sound awful! You do have a sound and the wood looks pretty but, and thats a BIG but, you will not get a good sound at all. I built a double neck koa and after two years now I am taking the koa top off and putting spruce on. I know it will sound so much better. As I stated the only reason I put the koa on top was because I wanted an all koa guitar, never again unless some one wants me to build them one. A walnut top has a very very dry sound, koa has too much high end but I did not know this. Keep the hard woods on the back and you won't be disappointed. I've been building for almost ten years now and every guitar I build is very different. I do not build to sell my guitars as I am on disability from car accidents, I can't afford really nice custom guitars so I am building what I would like to have.
cheers,.

Try Rick Turner. He might be able to shed some light on the subject.

Yes!

Absolutely!

You need to keep the weight down - as close to spruce as possible and watch the stiffness - again, as close to spruce as possible. Not to stiff, not too floppy.
That's really all there is to it.

God luck with that. It is not very easy.

Here is the method I used -
viewtopic.php?f=10101&t=22323

BTW - You can do it and have a good outcome, but it is tough. If the wood is figured, you might want to think about making the top a laminate - epoxy a thin layer of spruce to the bottom side. Again - watch the weight and stiffness. I've done this with figured redwood and I think it could work with other woods. I kept the redwood thicker than the spruce, but if I were using a hardwood, I'd make the spruce thicker than the hardwood to keep the weight down. This has been discussed before and you'll find that most people will tell you not to do it. I think if you want to try it, give it a go. You might come up with something nice.

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"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

I share your concern as i'm going to build a few with hardwood tops this winter.I plan on keeping the weight down on those top plates.

Is koa really that poor for tops? I really love the look of a koa top.

Thanks Steve, I must have missed that post. Lots of great info there.

Maybe I should be thinking about a double top method with the nomex and all. My hesitation is that sometimes gluing two uncommon woods together can have some hyper warping affects with changes in humidity. I wonder if that will happen with the nomex sandwich as well?

Sometimes I have come across a figured back set that has a spruce-like ring to it. This has got me thinking about its possible use as a top.

Jyme, I know what you are saying. It just seems a crime to hide spectacular zoot at the back of the guitar.

Thanks everyone for the input. I do want to try this so it is great to have the chance to ask so many builders at once. Especially when it's an off-the-wall topic.

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Wade
Nashua, NH
http://www.wadefx.com

Hi Wade,

I've built a number of different sized nylon stringed instruments with figured koa tops. Once I figured out how to get the top stiffness distribution right (I make a map of the top deflections and carve the braces until I get the deflection values I want) the instruments sounded just fine and the tops remained very stable. Details of the general process are here: http://www.ukuleles.com/Technology/compliance.html

It's important to remember that figured woods often have stiffness values which are only one half to one third the value of unfigured wood of the same species so it's necessary to make the top a little thicker. I also pore filled with epoxy to help stabilize the grain.

aloha,

Dave Hurd
http://www.ukuleles.com

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David C. Hurd
http://www.ukuleles.com

Alice laughed: "There's no use trying," she said; "one can't believe impossible things." "I daresay you haven't had much practice," said the Queen. Through the Looking Glass by L. Carroll

"Since my house has burned down, I have a much better view of the moon"

Hey Wade!

I would think too that the hardwoods would have a different cross grain to long grain distribution. Maybe the bracing should accentuate long grain stiuffness more than the 90 degree x style. Maybe fan bracing? I have not built one, I am just thinking out loud.

Wade, are you coming to the tonewood festival this month? Maybe you could bring the top.

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Burton
http://www.legeytinstruments.com
Brookline, MA.

Thanks Dave and Burton,
Just the kind of tips and info I was looking for.
I am thinking maybe using figured woods on top may be more appropriate or work better on a small-body guitar. If I was to try it on a mid-size or larger, I guess it would be a good idea to make a laminate sandwich or some such thing to cut the weight down and give it more stiffness.
let me know if this makes sense.
Are we trying to simulate the response of a spruce top or can we settle for a different tone?
Is the difficulty in trying to get a familiar or pleasing sound from such an instrument?
Thanks again,

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Wade
Nashua, NH
http://www.wadefx.com

Hardwoods usually have lower stiffness to weight ratios along the grain than softwoods. It's not uncommon to find Sitka or Red spruce that has a Young's modulus along the grain that's in the same range as some Indian rosewood: 14,000-16,000 mPa. The rosewood, of course, will be at least 40% denser, and most likely more like 80% denser. The one set of myrtle/bay that I tested was right in the IRW range for stiffness, and density, and it had higher damping, but one test doesn't mean a lot.

The stiffness of the top to bending along the grain will be proportional to the Young's modulus (E) times the cube of the thickness (H, T was already taken). If you assume that it's the long-grain stiffness that does most of the work of keeping things from folding up too quickly, then you want that E*H^3 product to be at a certain level. You can make the top as thick or thin as you like to get the stiffness to come out right, of course.

It turns out that for the sorts of straight-grained softwoods we use for tops, the E values pretty well track the density. If you think about it, this means that the denser the top is, the heavier it will end up at a given stiffness. The testing I've done on back woods shows a less consistent relationship, but since the densities do tend to be much higher, and the E values are not in proportion, this means that straight grained hardwood tops will be more than likely to end up heavier than striahgt grained softwood ones. As Dave has pointed out, figured wood loses a lot of long-grain stiffness, so the weight penalty will be higher.

It might be argued that you can make the top thin anyway, and beef up the bracing. I'm not a big fan of that solution to the problem, unless you do it by adding in a lot of little braces rather than just beefing up the usual ones. To me, that tends to make the top too 'lumpy', and hurts the high-end sound.

So, what's the beef with a heavier top? Well, there isn't much horsepower in a plucked string. You don't put a small engine in a big truck and expect it to be able to keep up. The guitars I've heard and played that have hardwood tops tend to sound OK if they're done right, but they are not very loud acoustically. This might be a good thing if you're planning on using a pickup, and playing plugged in most of the time. The extra mass will help avoid feedback troubles and allow you to use more gain.

The extra top weight also cuts down on the treble more than the bass, suggesting that maybe you'd have better luck making a smaller bodied instrument with that figured myrtle. Smaller guitars tend to be more 'treble balanced'. Another advantage of the smaller box is that you can make everything a bit lighter while still retaining the stiffness, due to the smaller span. This helps in the power department, as the area of the top doesn't go down as fast as the weight when you reduce the span. A hardwood topped 0 or 00 probably won't be as loud as a spruce topped one, but it might be louder, or 'carry' better, than a spruce topped Jumbo or Dread, and it will probably have a 'bassier' tone than the spruce topped 0 or 00.

Thanks Alan, When ever I finish reading your posts, the lights in my shop always seem a bit brighter, or is it crisper?
I guess I'll start with a smaller body design and go from there.
Thanks again everyone.

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Wade
Nashua, NH
http://www.wadefx.com

I've built over a dozen Koa topped guitars and all have sounded outstanding. They
had the warmth and punch of a softer Spruce, but were sort of rolled off a little in
the top end. Harmonically, they all had a nice balance between the fundamental and
harmonic blanket.

The Koa backs and sides that the tops were matched to provided the typical warmth
and strong fundamental projection that Koa always does. The Koa tops, when braced
correctly to allow them to make a contribution that is as close to their tonal potential
as possible.

The use of a Koa top with its flame that measures bwteen 1/8" and 1/2" from wave
to wave is a different prospect from that of using Redwood or other flamed woods
with figure that is much wider, measuring bewteen 1" and 1 1/2" between waves in
the flame.

The beauty of that type of flame is created by runout forming that patterns as the
grain runs in and out of the surfaces of the plates. If the bridge is glued down and
crosses a dozen or so of the waves, the footprint is much more secure and the integrity
of the joint is much better than if the bridge footprint covers a single cycle of the
flame runout. The chance of the bridge lifting and pulling off of the top while tearing
the top apart is much more when the flame is longer or wider as on many of the nice
looking Redwood tops that show up on guitars.

I still have a few incredible sets of Koa with tops, backs and sides that i', looking forward
to building all Koa guitars from in coming years. The trouble with the tone in all Koa
guitars has never been to woods used, but the failure of the builders to consider the
different characteristics of the Koa from those of typical woods like Spruces and Cedars.
They need to be addressed in very different ways when it comes to thickness, bracing
placement, mass and distribution and even graduation of the tops at the edges to
create a sort of cantilever section that allows much more free vibration of the entire top.

Regards,
Kevin Gallagher/Omega Guitars

Hey Wade,

I am working on a myrtle guitar right now so while I had the plates at the same shape and thickness I did a couple quick deflection tests. Both plates were .12 and 21.5 x 16. The results found that the myrtle was 1.46 times heavier than the spruce (421 grams to 288) while only .72 times as stiff. This was very curly so that may play a part. This is only a group of 1 so obviously it isn't overly meaningful but I thought since I had it here I would share it.

_________________
Burton
http://www.legeytinstruments.com
Brookline, MA.