Instrument makers have always tried to manipulate string length to optimize tone and feel, but how much is myth and how much is science?
Length, gauge, friction, voodoo? Revisiting the mystery of real or perceived string resistance in a science-y way.
In a previous column, I investigated the relationship between overall string length and its resulting tension ["The Doors of Perception," August 2020]. I cobbled together a crude measuring fixture and determined that the length of string beyond the bridge and nut did not affect a string's (linear) tension at a given pitch. After being assailed with comments and emails loaded with physics lessons detailing the math behind my conclusion, I now know that it was folly to assume any other conclusion. The laws of physics state that string tension is determined completely by the active (vibrating) length of the string, the pitch the string is tuned to, and the string's mass. In simple terms, this means that for a given vibrating length, the tighter you pull the string or the heavier the gauge, the more tension it will have. Nothing else, like peghead length or tailpiece position, matters—full stop. Still, the feeling persisted that I could sense a difference on instruments with long lengths of string between the bridge and tailpiece, such as an archtop jazz guitar. I'm not alone.
There have been many seasoned musicians I've known who swear that a flipped 6-in-line headstock tightens up the low strings. They've reported that the strings were tougher to bend and felt stiff. Some of the string manufacturers I spoke to in my research, despite their knowledge of the science behind the materials and construction of guitar strings, offered that there might be a perceived difference. But how could this be? You'd think that if you feel tension, it could be measured, yet my test instrument showed no change. Could there be another force at work, like lateral resistance? It seemed impossible, but it was time to resurrect the string tension fixture to find out.
My string test contraption was originally built to measure the linear tension of strings, but I only had to make a few changes to convert it to quantify lateral resistance. Admittedly, human fingers can detect minuscule changes in pressure, so I wondered if my 20-pound test instrument would have the resolution to pick up any variation. My theory was that if the overall length of a string was longer, there might be a perceivable difference in the force needed to stretch a string to a given interval. I'm counting on the physics majors out there to rush in at this point with the equation that I'm oblivious to.
Perhaps the friction (or lack of same) at the nut and bridge is what we are feeling when a guitar feels easy to play, or, conversely, when we say it fights us.
Nevertheless, my method was to use a pair of .012 plain steel strings and bend them the distance needed to raise the pitch one full step. Each string would have a different overall length despite their identical vibrating length. The full-step bend at the 8th fret position is a lick that all (non-classical) guitarists employ regularly. It's also the figure we often use subconsciously to determine playability when evaluating a guitar. I used this exact move in an attempt to impress Joe Bonamassa while sampling one of his '59 sunbursts. He avoided eye contact.
In my initial tests, I observed that it required a force of 1.8 pounds to raise the pitch one full step, regardless of the total length of the string, as long as the vibrating length remained 25.5". Thinking that perhaps the string's light gauge made any difference too small to measure accurately, I repeated the experiment with a .056 low E string. My test replicated bending the same B note three frets (a step-and-a-half) sharp to D. This is a pretty bold move on a guitar, but I thought maybe I'd see some evidence of difference if I really strangled it. Again, no difference was indicated, as both examples required 4 pounds of pressure to reach the higher note.
Now, I'm sure many of you will be quick to point out that this was a pretty shoddy exercise. I didn't make absolutely certain that the friction at the nut would be equal when extending the length to the tuner. Friction is a factor often brought up when this subject is discussed. Should I have used a ball-bearing roller at the nut? Perhaps the friction (or lack of same) at the nut and bridge is what we're feeling when a guitar feels easy to play, or, conversely, when we say it fights us. What about those players who have that little quivery vibrato that sounds like Joan Baez? Do they feel these forces? As for my research, at this point I was beginning to tire and made myself an espresso.
I'm hopeful someone smarter than me will figure this out and make a YouTube rebuttal. Meanwhile, I'm planning my next test to see if longer scale length is why Eric Clapton "lost" his tone after Cream. Until then, rock on friends!
Fig. 1 — Unlike the break angle at the nut, the break angle at the bridge has consequences for each and every note played.
The zen of break angle mechanics and why tone relies more on the tail than the head.
It surprises me how some details of our instruments are discussed obsessively, while others remain unattended. One such example is the intense discussion about nut material, which we touched on in October 2020's “Does Fret Material Really Matter for a Bass?" It's an interesting discussion, because a nut's DNA is close to obsolete once we fret a note, yet frets only remain a topic when it comes to dimensions and playability.
Another good example is the question of whether a tilted or straight headstock is the way to go, and what their different break angles mean for tone and playability. Guess what? It's another topic that's as good as irrelevant once we start using our fretboard! So, it should be no surprise when a bassist is baffled at how the feel and tone of his bass has changed after shimming the neck.
Shimming is about changing the neck's tilt by adding a thin piece of plastic or wood into the neck pocket. When it comes to bolt-on necks, it's a popular way to help with a bridge that has run out of its range of adjustment. Simply tilt/maneuver the neck backwards, and you then raise the bridge to get back to proper action, or vice versa.
Like the bassist who inspired this column, after doing his own shim, you might be wondering about the likeliness that a neck-pocket shim could be the source of altered feel and tone. Well, a tight and evenly routed neck pocket has long been seen as an important proof of quality, with some builders even removing potentially disturbing lacquer from the pocket area. With that in mind, yes, throwing in small strips of a credit card rather than a wedge-shaped piece of wood seems like a sacrilege. However, it's not like creating small gaps in a neck pocket qualifies as acoustic chambering. Shimming might reduce the neck's actual total-contact area, but the overall pressure is force per area, so it remains unlikely that any such small change would be heard or even felt.
Of course, our player did readjust his bridge after shimming, without thinking this could be the cause of the changes. Some of his colleagues even suggested that it felt and sounded different because the steeper the break angle, the higher the strings' tension.
Following is the formula for determining string tension (T) for a given frequency or pitch (F):
T = [UW x (2 x L x F)2] ÷ 386.4
Here, “UW" represents the specific weight per length unit of core and winding, while “L" is our scale length. Don't worry: There's no need to dig any deeper into this formula right now, except to simply absorb the terms involved. It is important to note that there is no mention of string length beyond the bridge or nut, and nothing about break angle or downward pressure. In mathematics and physics, this simply just means they are irrelevant.
Some musicians use the term “perceived tension" to describe their feeling of plucking a string, which comes a bit closer to our friend's concerns about his bass, but it absolutely collides with all things physics. Said perception is simply a matter of the elasticity to the string's elongation when plucked and moved out of its neutral position.
In a string, the core has to handle all the tension. Therefore, it has a significant and non-negligible stiffness that reacts to lateral movements of the string, which does highly depend on said break angle. The higher or steeper the angle, the higher the downward pressure.
Let's look at the two scenarios in Fig.1. Bass A has a break angle that's closer to zero—as in the case of a Fender-style 1-piece bridge—with just enough downward pressure so the string doesn't pop out when plucked. Meanwhile, bass B has a break angle closer to 90 degrees, representative of almost any string-through bass.
Plucking a string on bass A—with its slippery bridge contact—means it will be immediately lengthened from the anchor point of the tuner and tailpiece or bridge. With the higher downward pressure on bass B, there is far less slippage, which makes it more difficult for the part outside the scale length to stretch. It's less elastic and feels, well, harder.
It's not only about slippage, however. It's also about a different bending of the core. On bass A, the core stays relatively straight on both sides of the bridge, meaning that any core bending on the playing side causes a bending (and finally vibration) after the bridge, partially compensating for the core's stiffness. This doesn't apply to bass B since its core behind the bridge is perpendicular to the strings' movement, and is therefore unable to compensate. Since all bending of the active string happens on a shorter length, it results in a higher resetting force, which needs more power from your hand to get the same deviation of the string.
Whether you prefer the hard or soft feel—or something in-between—is simply a personal choice. And, as opposed to the nut's break angle, it has consequences for every note played.
Frets will wear over time, so to recapture playability and expression, players need to know when frets need leveling or replacement.
We all know dead strings can compromise our tone, but so can fret wear.
While it might be easy for players to see, feel, and hear their guitar strings wearing out, it’s less obvious to see worn frets, despite their sharing equal responsibility for each note. Fret and string interaction is fundamental to the function of a guitar, but many players give little thought to the influence frets have on the way our guitars work, and how we play them.
Though the earliest frets were little more than pieces of string tied around a neck and slid into position by the player, guitar frets have been made from metal for centuries. For much of this time, a fret was a simple, straight-sided length of metal hammered into a groove sawn into the fretboard. This method worked well—particularly with relatively large-diameter gut strings—because the player’s fingertip was largely on top of the string and didn’t contact the abrupt, straight-sided fret much.
As smaller-diameter steel strings became increasingly common, the player’s fingertips contacted the sides of the fret more than before, creating a distinctly bumpy, ridged feeling on the neck. In response, wire makers created what we think of as a modern T-style fret, characterized by its larger semi-circular top section held in place by a slender straight portion, and, often, small teeth embossed in the sides to bite into the wood fretboard. This style of fret makes for a smoother playing feel and is easier to install at a uniform height. That’s thanks to the built-in stop that bumps into the fretboard’s surface when fully seated.
Regardless of the fret’s exact cross-section, the most critical aspect is that the top of each fret is exactly the same level as those in front and behind it. If not, the vibrating string is likely to contact the unwanted high spot and create a buzz or incorrect note. The frets don’t necessarily require identical height between the fretboard surface and the top of each fret—only that the tops of all frets fall in an even plane with each other. In fact, this is a typical scenario for a guitar.
The issue is that when two metal things rub together, they wear. Mostly, the harder metal will wear away the softer metal. Guitar strings and their differing alloys and construction styles have a wide variety of hardness, as do fret wires. Frets are bound to wear unevenly as we play, progressing to the point where an often-played note is measurably lower in elevation than a less-worn fret, preventing the string from playing accurately. The remedy is to grind the tops of all the frets into a uniform lower plane with respect to the intended radius of the fretboard, and then reshape the sides of each fret to a semicircular cross section to restore accurate pitch and consistent playability to every note. Since frets in the lower and middle portions of the fretboard are typically subjected to more wear than the highest notes, each successive fret-leveling operation tends to result in slightly shorter frets near the nut, and slightly taller ones at the dusty end of the fretboard.
After establishing a uniform plane across the tops of the frets, a second consideration is the overall height of the fret. The distance between the depressed string and the fretboard surface significantly changes the feel and playing style of a guitar neck. Put simply, smaller frets will tend to offer more accurate pitch for each note, while larger, taller frets can offer more expressive notes.
When a string is pressed to the fret, our fingertips subtly bend the string sharp as we push toward the fretboard surface. And as our fingertips contact the wood fretboard, the extra finger pressure is distributed, preventing the player from raising the pitch any further. This bending effect is minimized with small frets since they somewhat limit the player from pressing too much and raising notes higher than the intended pitch. In contrast, tall frets can exaggerate a deviation from the intended pitch, but they also allow for a myriad of expressive effects. This is because the player’s fingertips have a high degree of control to bend down toward the fretboard or sideways to alter the nuance of each note.
Regardless of the style or metal alloy, frets will wear over time. They can be leveled a number of times, but once they’re too low to play comfortably, it’s time to replace them to restore playability and expression to your guitar.
