Q: I enjoyed a recent column in which you mentioned how headstock repairs can affect guitar tone. Internet forums abound with anecdotes of swapping out heavy tuners with lighter machines to improve the tone on certain guitars. Is there any truth in that? Having a PhD in physics, I also appreciated the physics flavor sprinkled throughout the article. I spend a lot of time thinking about why different guitars have different sounds. In theory it seems that one could predict the tonal properties of an acoustic guitar just by knowing all of the material properties and details of construction. But in practice I have learned that there is as least as much art involved as there is science. It’s fascinating to me!
A: Thanks for the kind words. Without question, the physics of stringed instruments is an intriguing and complex field, full of highly interactive variables and entirely subjective evaluations. People can spend—and have spent—whole lifetimes attempting to orient themselves on why instruments work the way they do, and how to predict or control the results in advance. Before we look at your specific question, I’d like to suggest a few rabbit holes for anyone willing to jump into the world of physics-based instrument building and evaluation.
The modern approach to scientific study of instrument behavior began primarily in the world of violins, with the incredibly influential work of Carleen Hutchins and Norman Pickering. From there, violin analysts such as George Stoppani have carried the torch forward, developing high-tech analytical tools using custom-written software, accelerometers, and laser holographic imaging to visualize plate behavior. Guitar luthier Alan Carruth was one of the primary bridges between the violin and guitar fields, and continues to be at the forefront of research on guitar performance.
Another important school of guitar research originated in Australia. Luthiers Graham Caldersmith and Trevor Gore brought new levels of rigor and scientific method to their building approach and published quite a few papers documenting their results both empirically and mathematically.
Finally, in the United States, a number of builders have begun using FFT (Fast Fourier Transform) software to evaluate and tune their instruments, both during and after construction. Specialized equipment such as the LucchiMeter is used to measure transmission speed of vibration through materials, allowing wood suppliers to sort wood according to sonic performance as well as mechanical and aesthetic properties.
Although many of these techniques have begun to show real results, I think it is important to mention that the gold standard of tone and performance for many makers remains the vintage guitars of the 1930s and ’40s, all built long before such scientific methods were developed. Instrument tone is inherently a subjective and constantly moving target, and analytical tools can only tell us so much, just as no scientific evaluation of a painting can accurately measure its emotional impact on the viewer.
Moving on to your specific question: changing the weight of tuning machines can absolutely affect the tone of the guitar, and I have encountered this quite a few times in my repair work. The neck and headpiece are quite a bit more flexible than many guitarists realize, and I will sometimes shock my clients by clamping the body in a vise and showing them just how easily the neck will flex with gentle hand pressure. On some guitars, it’s possible to yank on a single string and watch the others rise up higher above the fretboard as the whole neck bends forward.
This flexibility is one of the main culprits in subtracting energy from the vibrating string. The neck/headpiece system oscillates when excited by the string, and the rate of that oscillation will be affected by both the stiffness and weight of the neck. Loading the end of this oscillator is a particularly direct way to control its rate. Heavier tuners will slow the rate, which has two effects—it can contribute to sustain by adding inertia, but it can also potentially push the neck’s oscillation down into the musical range of the guitar. When this happens, some notes can sound weak or even dead, as the guitar will lose energy to the neck much more quickly at those specific frequencies. It’s quite easy to experiment with adding mass to the headpiece to gauge its effect—a simple C-clamp will do (padded, of course!), or one of the commercially available aftermarket products such as the Fatfinger sustain enhancer. For particularly flexible necks, these products can sometimes be helpful in shifting the problematic frequencies to a less problematic range.
Lighter tuning machines, by contrast, will provide less inertia, which raises the native frequency of the neck/headpiece system. This is why some players perceive an improved tone after switching to lighter machines. The dead spots often shift higher into a range that does not compete with commonly played notes. It accomplishes a similar effect to making the neck more rigid, but much less invasively. Lighter tuners also noticeably improve the balance of an acoustic guitar, reducing “neck dive” and overall weight.
Every guitar must be considered in its entirety as a physical system, and different makers have different priorities and preferences in their work. The late Rick Turner often expressed a preference for heavier, more rigid necks in his instruments, while other builders, such as Ken Parker, have engineered brilliant systems to build necks that are both lighter and stiffer than the traditional solid mahogany and maple. Both approaches have their adherents—and both can yield remarkable instruments.
Uncertain about guitar care and maintenance? The ins-and-outs of guitar building? Or another topic related to your gear? Ask Acoustic Guitar’s repair expert Martin Keith by sending an email titled “Repair Expert” to Editors.AG@stringletter.com and we’ll forward it to Keith. If your question is selected for publication, you’ll receive a complimentary copy of AG’s Acoustic Guitar Owner’s Manual.
This article originally appeared in the July/August 2023 issue of Acoustic Guitar magazine.