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We went shopping today, and as long as you're near the Woodcraft store: you might as well go there. A 1" X 8" x 88" piece of Padauk called out to me. I saw a piece of Purple Heart too, for a one piece archtop. But it was 2" thick! A shame.

I think I can get two arch tops out of it, with sides; I'll have to plan it out. I was going to use a piece of Cherry, but I still don't have any cherry sides. I have a piece of Paudauk that is similar, but doesn't have all the electric orange bands. That is for those little early 19th century guitars that are fun to make.

Has anyone made an archtop from Padauk? I thought of making a 7 (13) string Vihuela in G that would be like a guitar in drop D with a high G. So maybe a 7 string guitar in drop D with a low A to bring it up to date.

Longer scale. I watched a video of two guys playing 7 strings that is crazy good. I saw a video of an Alan Carruth 7 string before that. I had no idea there we such a thing.

I don't think it is terribly heavy; maybe like hard maple? The pieces are too heavy to weigh on may little scales. The other Padauk I've used is different. More ribbons, more purple, curly. It was .67 sg; probably because it is 20% pores!

The board was only $75. If I can get 2, that's less than $40 each. Now if you could only locally source spruce!

Photos never get the color right. The original photo is way too brown. The other is sort of right, but the boards have orange that doesn't show up at all! Weird.





https://www.youtube.com/watch?v=wAAbQWAYW3s

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Why be normal?

I love Padauk, especially the smell…

I made my first archtop Classical guitar out of Padauk. I'm not sure I'd use it for an archtop again.

I chose it because it is a reasonable replacement for BRW, with similar density, stiffness, and damping, but much lower in price (I got mine for $5/bd ft, but that was a long time ago). It turns out that, although low damping generally good, and particularly on a Classical, you don't really need to use a low damping wood for the back of an archtop. A carved arch ends up with lower damping anyway, simply due to the arch height. The arch raises the resonant pitch of the 'ring' mode but the band width stays the same, and damping is F/band width, so the effective damping is low. An arched maple plate can act like a flat rosewood one. Starting with a low damping wood can give a band width that is too narrow to couple effectively with top resonances, so it actually doesn't work as well.

Another issue with Padauk is that it is very prone to splitting when bent across the grain. I kept getting cracks simply from flexing the plate in the normal course of carving it. I hoped that gluing the back to the rim would stop that, but when I took it to a GAL convention the airliner baggage handlers managed to 'modify' it anyway. I ended up having to glue up two long back cracks with CA to show it. Since then I've been careful to put tape across the ends of pieces of Padauk as I work them to help hold them together.

I've been using that batch of nicely quartered Padauk for experiments since then. I've used it for backs on 'test mule' guitars, and also for the oddball harp guitar I made for an on-line challenge. It's also good wood for teaching finish methods; particularly French polish. It has pores the size of soda straws, so you get lots of practice filling...

Interesting Alan,

I made a guitar, and a violin out of a piece of curly quartered Padauk. The edge of board near sap wood was unbendable, with micro cracks everywhere, but I found enough to bend ribs. I had no problem with the backs at all. It IS full of pores. I used Aquacoat to fill the violin, but I don't really like the look of it under the varnish. It looked good before the varnish. I just use Osmo oil on the guitar, and I really like it with that. It looks like wood!

I have a Sitka cello belly that I found a bunch of micro cracks in the summer grain, so I need to make a new one. I also had a Red spruce violin that kept splitting on the grain after it was all done. I threw it away! So top wood can be trouble as well.

And. My curly redwood archtop was a scary thing to carve. It seemed like you.could break it by looking at it. very flexible. Two coats of Zpoxy made the surface somewhat harder, but you could easily snap off a wing. But it works really well, even with steel strings on it now.

Maybe having it cut for flat tops would be better. I know NOTHING about acoustic terminology. About as much as I know about electricity and computers. Nothing. Violin makers talk about A0, A1, b whatever. I did FFT graphs of 4 vastly different violins I made, and the lower peaks up to 500 or so were all about the same! One is easier to play, but despite being different models, different woods, and different strings, the sound like violins to me.

My archtop sounds way different than my little Stauffer.

Now to do an archtop I need to find some cherry for sides.

To make flat tops I need do get some tops.

What exactly does low damping mean? Low damping is why Padauk rings like crazy, and oak is dead as a door nail? Doesn't it still ring like crazy carved? I don't remember the violin going dead on.me. Are you saying that it looses complexity? It seems that arching adds complexity.

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Why be normal?

Damping is a measure of the rate at which vibration energy is dissipated in a system. If you're thinking about AC current, then damping is analogous to resistance in a DC circuit. It's often expressed as a 'Quality factor' or 'Q-value', with high Q values denoting low loss. A material that has a Q=100 dissipates 1% of the energy of the system (ultimately as heat) per cycle of vibration. Since this works like compound interest, after ~72 cycles the vibration energy would be 1/2 of what it was at the start, or 3 dB lower. Note that if it's vibrating at 100 Hz that takes .72 seconds, while at 1000 Hz it's .072 seconds, ten times faster. Tapping on a piece of high Q wood, such as typical Brazilian rosewood (Q~150) give a longer 'ring' than a lower Q (higher damping) wood such as maple (Q~70).

Another noticeable thing about high-Q systems is that they give a more secure sense of pitch. Low Q systems are harder to drive to high amplitude, even at their resonant pitches, but, by the same token, they're not much harder to drive off resonance than on it. The response is spread out over a wider frequency range, so you don't get the strong impression of pitch with a low Q material. They make xylophone and marimba bars out of rosewood rather than, say, oak (Q~70-100) to get the better pitch. Aluminum has low damping (I've measured Q~ 10,000 or better): it makes good tuning forks and 'vibraharps'. Low damping systems make good time bases: quartz crystals run up in the million range.

It seems to me that when you're talking about a guitar the damping of the wood is only a part of the story. Basically, I thing it sets a limit: you could not make the instrument have a higher Q value than the material it's made out of. Sadly, it seems to be all too easy to end up with higher loss, lower Q. Using the best wood is not a guarantee; the maker still has to avoid messing it up.

Alan, have you ever noticed in carving, that sometimes it just opens up? Or when I carved the cross braces on the Stauffer way down to nothing at the edge, and shaped them like a bass bar. It feels like the wood was in the way? Maybe it doesn't sound like a 1829_Stauffer, but I don't have a clue what one sounds.like!

I like tapping.wood, but what can you really gather from.it? A curly birch violin back was low pitched from the start, but the really high arched, really light Englemann top works great with it. I don't put any stock in free plate tuning, but.they were probably a fourth of fifth apart!

What is it that.makes some wood, have.a.deeper sound? (same basic shape) And some have a more complex sound, not just a fundamental? Some are clear. Many are muddy.

I do like to go thin though, so even if I just it for flat.tops, and bending,.I'll have to be.careful. I was careful with the curly redwood because I was warned. And it.felt.like you could easily snap it in poeces.

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Why be normal?

"Alan, have you ever noticed in carving, that sometimes it just opens up?"

I've seen that sort of 'threshold effect' a lot. Sometimes it happens when you shift the pitch enough to move out of, or into, the band of some other resonance. This is the sort of situation you get when you swap bridge pins and hear a real difference.

"A curly birch violin back was low pitched from the start, but the really high arched, really light Englemann top works great with it."
The first instrument I 'tuned' with Carleen Hutchins was a 15" viola that had come almost completely unglued in somebody's attic. The wood was beautiful but it had never sounded good, according to the friend who gave it to me. The top was light and tight grained, and the back was extravagantly curly. The back was so flexible that the top had to go very thin to work with it, but it held up OK and sounded about as good as a 15" viola could.

You're right to be skeptical about simple rules of thumb. I don't obsess about the pitches of the plates much these days, working mostly with mode shapes. I do try to match the #2 mode pitches on fiddles, and the 'ring' modes on archtop guitars; these seem to give results that carry through to the finished instrument more reliably. At any rate, the system does seem to work for me, so I'll stick with it. It's also possible that in ~50 years in the business I've picked up some skills I don't even know I have.

I'm sure that you notice things most wouldn't. As a CNC machinist I could tell when carbide inserts were getting dull by the chips, or even by the sound.

I think many instruments are made empirically, with no real input buy the maker. Surely all production.models are. Working to numbers of some kind: deflection, weight, tap tone, or combinations.

I tested deflection on the last violin for the first time. It felt floppy, but the belly barely moves .005 over the bass bar, and .02 over the sound post area.at the bridge. The back moves .01 at the bridge area. It seems like a good idea to have the back move somewhat less, but I'd need to do several to have any idea how much less.

A viola or cello would be different.

Watching Driftwood guitars, 3,000.year old guitar build (a nice series, I haven't watched it all) I see that he uses laminated.sides specifically for increasing sustain on the belly. Would.that also transfer.more sound to the back? There is no sound post for coupling. Would stiffer sides themselves transfer sound?

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Why be normal?