Scale length is the length of the string from the nut to the bridge. This is the active part of the string that vibrates when struck. Scale length measurements do not include string ends above the nut and below the bridge. Generally, a longer scale length means a greater distance between each fret and a longer neck. For instance, the mandolin has a short scale length while the guitar has a longer scale length. The guitar has a greater distance between each fret. The upright bass has an even longer scale length.
Different types of banjos have different scale lengths. A standard scale length for steel strung open back banjos is 25.5 inches. Some open back and gourd banjos have shorter scale length. A banjo with hard-tension nylon strings performs well with a scale length as short as 22.25 inches. Many resonator banjos feature a longer scale length, around 26.5 inches.
Fret spacing is derived from scale length and can be calculated using a mathematical formula. When a player uses a fret, they are changing the active length of the string, resulting in a different note. Precision placement of frets is essential for intonation. Intonation is how in tune an instrument is with itself.
Scale Length & Strings
The relationship between scale length and the tension needed to bring a string up to pitch has performance implications. If a string is too slack when tuned to pitch it may fail to generate enough energy to sound good. It may also buzz against the frets. If a string has too much tension it may break! The correct tension for any given string is somewhere between these two extremes. Somewhere around 80 or 90 percent of maximum possible tension may deliver the optimal steering energy while avoid serious risk of breakage.
String tension affects the tone produced by an instrument, and tone is highly subjective. Slack tension may produce a tonal feel that suits a particular piece of music. So, while having an objective understanding of scale length and tension is helpful, it’s also helpful to situate this knowledge within the realm of artistic and creative endeavor.
String gauge is a measure of string diameter. Thousandths of an inch is a common unit of measure for string gauge.
String material, length, and gauge all affect the weight of a string. A length of steel string weighs more than the same length of nylon string of the same gauge. This is because steel is denser than nylon. As string length increases, weight also increases. Also, string weight increases as gauge increases. Heavier strings require greater tension to bring them to pitch. A string under more tension produces vibrations of greater amplitude and results in greater volume.
Short scale instruments often use larger gauge strings. Light gauge strings that feel good on a longer scale instrument may feel floppy on a short scale instrument. Why? The shorter the scale length, the less the total weight of the active length of the string will be. A string of lighter weight requires less tension to bring it to pitch. Lower tension typically results in vibrations of lower amplitude and less volume. It may take some experimentation to find the optimal string for a particular scale length or a particular tuning.