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I'm coming to a close now on number one, a few weeks yet, but I started selecting some tonewoods for the next builds, and wondered how you go about doing this correctly what you should listen for, feel and see. The tops I bought were classed as c5 they had knots, colouration, I was advised by the dealer a luthier to take my template for the body shape and he sorted the best 5 out of a big pile where my pattern missed the problems. Now I made my selections for two reasons which I'll explain, then hope that you'll be able to tell me what type of tone they are suited too. They where both european spruce and I selected them for the following reasons

1. The reason I selected the first set was because both pieces when held in the corner and taped gave a short bass heavy thump which was quite short lived.

2. The second set I selected was because when held and taped it had a higher pitch than the first, but with substantially more sustain.

I don't know if these are valid reasons but they were my current thoughts. Also I've been told with back and sides the glassier the tap tone the better when I get that far I'll choose the sets for that sort of reason, but will probably post here first.

Thanks

John

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Formerly JJH

I learn more from my mistakes than my successes

Usually we're trying to get the top to be as light as possible while still being stiff enough to hold up under the string load. This would indicate a high ratio of stiffness to weight would be desireable, and that translates into a high pitched tap tone for the top. There are several different ways you can hold it when you tap, but, in general, you're looking for a nice, high tap tone.

Plucked strings don't deliver a lot of energy to the soundboard, and we usually can't afford to waste any of it. One of the big wasters is the damping factor of the wood, so it's usually good to pick a piece that has as low damping as possible. The two symptoms of this are a long ring when tapped, and clear impression of pitch.

You have to keep a few things in mind though. One is that the top is going to lose a lot of energy to the air as it vibrates, and if it is very light it's not going to have the momentum to kep vibrating for a long time, no matter how low the internal damping factor is. I've tested a couple of large pieces of balsa wood, and find that they have about the same sort of damping as spruce. It's just so light that the thin pieces you usually see die out fast from moving air. Another is that top woods that have low damping may also have other properties that make them less desaireable from a beginner's standpoint. Western Red Cedar usually has low damping, low density, and high cross grain stiffness, but it's soft, easy to dent, and splits more easily than most spruces. I would tend to decide on the type of top wood I'd be interested in, and then look within that pile for pieces that had notably low damping and high stiffness for their weight. Finally, remember that stiffness increases much faster than mass as the piece gets thicker: a floppy but thick piece of wood could have a high tap tone pitch. You get better at taking that into account with more experience, but most of us probably aren't as good as we'd like to think we are. That's one reason I, and others, have been doing more technical testing.

The back has a different job than the top, so you're looking for different properties. In particular, it seems to me that you want more, rather than less, dense wood for the back, while low damping is much more important. The back doesn't do much to contribute directly to the power output of the guitar, and most of the energy that goes into making it vibrate is wasted; stolen from the more effective top. A heavier back will move less, and steal less energy from the top. Similarly, a back with low damping will not be easy to drive into vibration except in very limited frequency ranges. A dense back with a low damping factor tends to work out well, then.

Again, there are obvious exceptions to this rule, as to all simple rules. Part of the 'mahogany sound' has to do with the relatively low density of the wood, and part of the way maple sounds is probably from it's relatively high damping as compared with a rosewood. Again, as you gain experience, you'll get to know what to expect from various wood types, and plan the woods to use based, in part, on the sound you're trying to get.

I guess this is why acoustic guitars cost so much even though the material cost may be 1/4 the price of the actual cost of the guitar. You're paying for labor and experience.

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Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

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