Starfire IV neck wood. Maple,Mahogany

DThomasC

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I had no idea Louis CK was working for Fender now!

Seriously, that was an interesting video, but also disappointing. Yeah, I'm going to go ahead and be that guy; the guy that thinks he knows something about guitar making that Fender doesn't. Here's the thing, on some other forums I regularly read comments about how silly tap testing is, that all you learn is the fundamental resonant frequency of that particular board, and my reaction is "No!!!, You're not listening for the fundamental. You just don't get it!" And then some guy from the Fender Custom Shop starts whacking neck blanks with a mallet...

It was a long long time ago, but I spent two years as a violin maker's apprentice. One of the things that my maestro really enjoyed teaching me was how to listen to a piece of wood. We spent a lot of time trying to distinguish between otherwise similar pieces of spruce and curly maple, but we also spent an afternoon at a local hardwood store that caters to all sorts of craftsmen and furniture makers. (Pittsford Lumber, for anyone familiar with the Rochester NY area.) This gave us an opportunity to listen to a wide variety of species.

Anyway, he taught me how to not just hear the fundamental frequency, but to hear the timbre of the wood. He romantically called it the woods voice. Seems abstract, but it's such a simple and obvious thing that I don't understand why nobody else gets it. Imagine Al Green and Norah Jones both sing the same note. The difference is the timbre, the voice. Now suppose you have them sing different songs. Would you get hung up on the fundamental notes they sang, or would the differences in their voices still be fairly obvious? Why is it lost on even Fender Custom Shop master luthiers that the same is true for tap testing wood?

Scientists identify two types of properties: intensive and extensive. The lowest resonant frequency of a particular board is an extensive property. It belongs to that particular board. Cut the board into smaller pieces and the property will change. The property that we're interested in, whatever it's called, is an intensive property; it's intrinsic to the material itself no matter what shape it happens to be cut in to. If we're interested in a property that is intrinsic to the wood itself, then we should avoid being distracted by properties that depend on the size or shape of a specific board. That's true even if we hope to use that board in a guitar because we will almost certainly cut the board into a different shape. The extensive properties of the board at the lumber yard will be long gone, but the intensive properties of the wood will remain.

I went looking for a video showing the right way to tap test an arbitrary board, but found nothing. At least this guy understands that you can get different vibrational modes by hold the piece at different node points. It's old news to anyone that has played touch harmonics on a guitar.

So the technique that I was taught, was to try to find many different modes over the course of a few seconds. This allows you to assemble, in your minds ear, a general idea of the character of the woods voice. With a board up to about 5 feet long or so, you can start by supporting the the board vertically between your thumb and index finger, maybe 1/3 to 1/2 of the way down from the top. (Obviously, you're forcing a node where you're holding it.) Gently tap the board with a knuckle all over, up and down the piece. It'll talk back differently depending on where you hit it.

Now slowly let the board slip through your fingers a little at a time, thus moving the node. Continue tapping all over. Just like with a guitar string, you'll find that holding it at certain points along the length will produce strong resonances. Those are interesting and fun, to be sure, but it's not just those harmonics that you should be listening to. The wood is talking all the time and some of its character is easier to detect when there isn't a massive harmonic.

A couple of years ago I was visiting Pittsford Lumber again and I ran my fingertips along some spanish cedar. It almost sang to me and I literally felt that thing in my spine that you feel sometimes. They still have lots of spanish cedar, but none of it seems to sing like that board a few years ago. That wood revealed a lot about itself without anything close to a resonant mode of the entire board. They wanted a lot of $$ for it then, so I didn't buy it, but I really wish I did. Do I have not-buyer's remorse?
 

fronobulax

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Thanks for the videos. I think my problem is I am hoping for some scientific rigor that is not, and will never be, possible. In the absence of that rigor, anecdotes from people with serious and credible experience are the best I will get. The Fender guy said "different, not better" which is reasonable. I find I have a knee jerk reaction, often negative, to comments that say "better" but not "better, in my opinion or experience". Let's see how well I remember these lessons the next time something comes up :)
 

fronobulax

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On tap testing...

I think you can make more correct predictions about how a guitar will sound if you tap tested the wood than if you didn't and just grabbed the next slab in the stack. However there are more modes of vibration than what a mallet can produce and predictive accuracy can be improved by different tapping techniques and locations. Whether that improved predictive accuracy is significant when building a solid body I will leave to others to decide.

I heard someone at New Hartford or Collings or maybe both talk about tapping and wood selection. They were clear that there was more to their process than just a couple taps in one place. I seem to recall a demo of two potential guitar tops that sometimes sounded the same but sometimes sounded different depending upon how, where and with what the tapping occurred. My take away is that it was an art that could be taught by experience.
 

DThomasC

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There is an interesting part of the first video. There has been an Internet debate about the relative stiffness of flat sawn vs quartersawn necks. Some people assert that quartersawn necks are stiffer. This assertion is not typically based on any evidence, it's apparently taken as intuitively obvious. Others assert that there is no difference in stiffness. Evidence for this assertion is the fact that text books about the properties of different wood species typically make no distinction between flatsawn and quartersawn when discussing strength and stiffness. (Stability is a different matter.)

Anyway, in the video the quartersawn neck had a higher resonant frequency than the flatsawn one, which would support the notion that quartersawn necks are stiffer.
 
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