One of the core aspects of the art of lutherie is understanding wood on its most basic levels. Everything from the cell structure to grain spacing, grain orientations, growth patterns, density, and more, are on my mind as I look at a potential piece of wood for a component of a guitar that I’m working on.
Some of the most critical components on the guitar to select wood for are the tone bars. These small bars or braces, usually made of Spruce, enhance the structural integrity of the guitar top as well as function to shape the behavior of the top as it is in motion, thus setting the tonal parameters of the guitars voice by limiting certain frequencies and encouraging other frequencies to vibrate more easily.
When selecting wood for these elements it is vitally important to be sure that you know exactly how the strength and flexibility of each piece is behaving. What I’m after is consistency, I want to be absolutely sure that each tone bar is as consistent as possible from end to end. The amount of variation from piece to piece never ceases to amaze me, even if they were side by side in the tree.
Hand Splitting Spruce Tone Bars
If we want the highest stiffness to weight ratios and evenness of tone possible, the above mentioned variations present in most wood make it critical to hand split the wood for the tone bars. By splitting the wood you get to see how the wood breaks along its natural growth lines. This will reveal many things such as grain run-out, twist, knots, and other secrets of the wood that would go totally undetected if the tone bars were simply cut out of a block of wood with a power tool.
Once I have the wood split to a close enough tolerance, I then use my hand plane to bring them down to the final rough dimensions. I also do further fine tuning to be sure I have the absolute best quarter cut grain orientation and that the grains will run perfectly parallel with the center line of the bar. If either of these two things are out even a small degree, it has an enormous effect on the bars strength and consistency.
Strength and Tone
Now that I have all the bars split and fine tuned to my rough dimensions, I can test each bar for strength and tone. I test the tone by dropping them one by one on a steel table, listening to the sound they make as they hit. I might also sometimes hold them like a drumstick and tap the ends to hear the sound they create. I make notes of this data and then I flex each bar individually, sorting them into groups from stiffest to weakest.
Building For Tone
From there I choose which bars will work best in the design I’m working on. It is not always the same, there is no formula, the critical thing is that with this method I can be sure that my bars are totally optimized for strength, consistency, and tone. I can also be confident that I’m adding the right ingredient into the design to achieve the desired tonal and structural outcome.