From the January/February 2023 issue of Acoustic Guitar | By Martin Keith
Balance between the neck and body of an acoustic guitar is important to the sound and playability of the instrument. Neck weight, wood density, and other factors come into play when calibrating the right neck-to-body weight ratio.
How important is the weight ratio between the guitar body and the neck—would it be impossible to play a guitar that has a neck heavier than its body? Also, if I wanted to make a guitar using a very heavy wood, how would that affect the sound, and which type would you recommend? —Sarah Belal
I’m glad you asked! As with nearly every design-level consideration, this seemingly simple question leads us down quite a few different paths, all of which are worth exploring.
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The first and simplest aspect of the neck-to-body weight ratio is balance. Acoustic guitar bodies are generally fairly light despite their size. As a result, a heavy neck can easily result in an instrument that is poorly balanced, whose neck falls towards the floor when not supported by the player’s left hand. Players who find this particularly annoying will sometimes replace their tuners with lighter-weight models, in hopes of improving the guitar’s balance. This can work quite well, but these players often discover that the tone and response of their guitar has changed along with the tuners. This somewhat surprising fact leads us to the deeper discussion of the role of the neck in tone production.
Traditional acoustic necks are mostly made from mahogany or maple. These time-tested woods offer a good mix of strength, stability, medium weight, and easy workability. The tones they produce have defined our understanding of what guitars sound like, and thus we should expect that substituting other woods will make guitars with less familiar (and potentially less marketable) tones.
The energy produced by plucking a string is finite and drops off fairly quickly after the initial attack. Most of the tone qualities we try to describe—sustain, compression, etc.—are all functions of how the guitar absorbs the energy from the string. In fact, it’s useful to think of every aspect of the guitar in terms of how it subtracts energy from the string—how much, at what speed, and at which frequencies. The most obvious is the top, or the engine of the guitar, which is driven to vibrate by the strings, engaging the air pump of the guitar body to produce sound. However, nearly every component of the instrument will vibrate when the instrument is played, and most will affect the tone, even though they don’t contribute to actual air movement.
The neck can be thought of as a pendulum which swings back and forth when excited by the string energy. The factors that will affect the swing of that pendulum are its length, its weight, and the stiffness of the “string” that it swings on, which in this case is the actual neck material itself. A heavier neck will have more inertia, and thus will be less likely to move from the string’s small energy input. This inertia lowers the resonant frequency of the neck assembly, by slowing it down. By contrast, a rigid neck will be less likely to move because it is more resistant to the back-and-forth movements of vibration, which raises the resonant frequency by creating a shorter period of oscillation. Although they have different effects, increasing either (or both) of these factors will yield a neck that reflects more of the string energy back into the string, promoting sustain and a longer note envelope.
Even the headstock itself can have a meaningful effect on the guitar’s tone. In my repair work, I have fixed many (many, many!) broken headstocks. For some of the worst cases, I have laminated rear layers of ebony or other dense woods as a cap to keep the broken neck together. It’s not uncommon for players to report an improvement in the guitar’s tone and sustain after such a repair—the stiffer headstock loses less energy to vibration, and thus more energy is left to drive the top and produce sound. On electric basses, it’s possible to move or even eliminate the classic fifth-fret dead spot by pressing the headpiece against a wall, or by clamping weights to it.
With most woods, weight and rigidity travel together—heavy, dense species such as ebony, rosewood, wenge, oak, and others tend to be strong and stiff, whereas lighter types such as spruce, poplar, and basswood are less so. Some makers have developed necks using these heavy, dense woods, either as strengthening laminations, or even as solid wood necks; recent PRS instruments with rosewood necks are a great example. Other intrepid boutique builders have been experimenting with wenge and other high-density hardwoods as primary neck materials. Modern luthiers and even some factories have also begun tipping the scales (pun intended) by adding carbon fiber, titanium, and other lightweight stiffening materials to their necks to increase rigidity without adding significant weight.
What should the maker expect from a dense hardwood neck? In my experience, these woods contribute a bright, lively tone with a more percussive attack, noticeably increased sustain (due to both their stiffness and their mass), and some natural compression—likely the result of the neck reflecting more of the string’s energy back into the vibrating length. The weight difference will be quite noticeable, and players who play standing up may be particularly aware of the altered balance. I will also warn you ahead of time that carving a wenge or rosewood neck is quite a workout, much more so than good old mahogany.
It is an exciting time for the world of alternative guitar woods. Traditional materials are becoming more and more difficult to source in good quality, and new choices are emerging each year. Woods that were once very uncommon (wenge, katalox, ziricote, manchinga, t’zalam, and others) are becoming more and more accepted by builders and the markets they serve. At the same time, players are opening their eyes to the new spectrum of sounds that these woods produce. Although tops, backs, and sides are the most common places for innovative builders to experiment, neck materials can absolutely have a big effect on the tone and response of an instrument, and it’s a great place to explore. If you use a bolt-on neck construction, you can even build multiple necks from different materials, allowing direct comparison of the neck’s tonal contribution. As more and more builders begin to realize the impact of neck wood on guitar tone, I think we will see more and more alternatives beginning to appear, which is great news for both builders and players.
This article originally appeared in the January/February 2023 issue of Acoustic Guitar magazine.