Set Up - it's not rocket science, but requires knowledge & skill - Dec 2006
Correct set up of a stringed instrument doesn’t require sophisticated computer algorithms, vector Calculus or magical incantations. However, setting up an instrument to play easily, in tune and without buzz does require understanding of the physics of stringed instruments and some finesse. A lack in either of these two areas generally results in poor set up.
Relatively few amateurs learn the details and practice set up techniques, but those who do can set up their own instruments with predictable, repeatable results. The amateurs who try to short-cut the learning and practice far outnumber those who do their homework. While well-intentioned, these folks overlook important aspects when they attempt to set up an instrument and end up with instruments that are hard to play, cannot play in tune and buzz. Unfortunately, some of the modifications made during such a ‘set up’ require significant effort to reverse. The mistakes can get expensive.
If you do not want to study and practice set ups, do yourself a favor. Pay someone who has studied and practiced. The mistakes you are likely to make will cost you more to repair than the set up would have cost in the first place. If you are interested in learning about instrument set up, here are the things you need to study:
Understand neck-to-body angle. Acoustic and electric guitars and basses, mandolins, banjos, violins, violas, celli and double basses are the most common stringed instruments. While each differs from the other with respect to the angle that is optimal, all of them share the feature that the neck tilts back slightly from the plane of the instrument. This angle elevates the strings above the fingerboard and soundboard. When the neck is at a correct angle, the strings pass over the nut and the bridge/saddle low enough for the player to easily press the string to the fingerboard, but high enough to prevent buzzing.
Understand fingerboard relief. Strings on an instrument vibrate when struck/bowed. The string does not move at the nut, at the bridge/saddle or at any location where the player fingers the string. However, everywhere else, the path of the vibrating string traces out an arc. If the fingerboard is close to the string (generally considered desirable), it must have ‘relief’ to accommodate the string vibration. Rather than being ABSOLUTELY flat, the fingerboard must have an arc that mirrors the arc of the vibrating string, or the instrument will buzz.
Understand fingerboard and bridge/saddle radius. Classical guitars, most banjos and many mandolins have fingerboards and frets that are flat side-to-side. The fingerboards on teel string guitars and basses, some mandolins, a few banjos and all violins, violas, celli and double basses, however, are not flat. Instead, their fingerboards arc from side to side. Some fingerboards have one radius all along their length, other fingerboards change from radius to another from one end to the other. To achieve optimal playability, the bridge/saddle must have a radius that mirrors the radius of the fingerboard.
Understand nut height and radius and nut-slot depth and width. The nut is one of the anchor points for the string and, therefore, important to vibration transfer from the string to the instrument. The nut, setting the height of one end of the strings, is also important to playability. Like the bridge/saddle, the radius of the nut and the slots in it must mirror the radius of the fingerboard. The height of the strings where they pass over the nut must be low enough to facilitate fingering, but not low enough to cause buzzing. The slots in the nut must be deep enough that the strings do not pop out of them during play, but not so deep that they mute vibration. The slot width and shape must snugly fit the string diameter, allowing easy tuning without binding or slop.
Understand bridge/saddle height. The bridge/saddle is the other anchor point for the string and, therefore, important to vibration transfer from the string to the instrument. The higher the bridge/saddle, the longer the string required to pass over it. The longer the string, the greater the tension will be in the string. The greater the tension, the greater the vibration transfer will be to the instrument. However, the bridge/saddle also sets the height of one end of the strings and is, therefore, important to playability. The higher the bridge/saddle, the farther the string is from the fingerboard. With an ideal neck angle (see above), a set up can achieve high bridge/saddle to maximize vibration transfer while maintaining low string height over the fingerboard. If the neck angle is not ideal, the set up must make trade-offs to achieve playability.
Understand scale length, string gauge and tuning. The pitch that a string produces when struck or bowed depends on the string’s length and mass and the tension in the string. From experience, you almost certainly know that shortening the length of a particular string or increasing the tension it makes the pitch that the string produces higher. You may not have noticed a thicker (more massive) string that is the same length as a thinner string requires more tension to achieve the same pitch (frequency); many people are not aware of that relationship. Many people are also unaware that the mass of a particular length of string, not the diameter, is the reason that more tension is needed.
The equation shown here illustrates the relationship between pitch, string length, string tension and mass:
f represents frequency or pitch,
L represents the string’s length,
T represents the tension applied to the string and
p represents the mass of a particular length of string.
For an instrument to play in tune, without buzzing, set ups must properly adjust string length to accommodate string gauge and string height.
As you study, you will find other terms such as 'break angle' and 'takeoff point' that are important. This article cannot and is not designed to be a tutorial on set-up. The topic requires more effort than a single article can accommodate. Neither can this article impart the second component of successful instrument setup - finesse.
Finesse is an attribute that requires patience and practice. Armed with sufficient understanding and patience, you can do set ups. If you decide to try, start with less expensive instruments, preferably your own. Set up and repair of expensive instruments and the instruments of others are projects are for experienced hands.