Nut (string instrument)
The nut of a string instrument is a small piece of hard material that supports the strings at the end closest to the headstock or scroll. The nut marks one end of the vibrating length of each open string, sets the spacing of the strings across the neck, and usually holds the strings at the proper height from the fingerboard. Along with the bridge, the nut defines the vibrating lengths (scale lengths) of the open strings.
The nut may be made of ebony, ivory, cow bone, brass, Corian or plastic, and is usually notched or grooved for the strings. The grooves are designed to lead the string from the fingerboard to the headstock or pegbox in a smooth curve, to prevent damage to the strings or their windings. Bowed string instruments in particular benefit from an application of soft pencil graphite in the notches of the nut, to preserve the delicate flat windings of their strings.
The word may have come from the German Nut (pronounced "noot"), meaning groove or slot. (The nut, however, is called Sattel in German, which means saddle, whereas the part of a guitar known as saddle in English is called Stegeinlage in German.)
Not all string instruments have nuts as described:
- Some guitars and mandolins, for example, have nuts that are just string spacers, with deep notches. These instruments use a zero fret, which is a fret at the beginning of the scale where a normal nut would be. It is higher than the other frets to provide the correct string clearance. The zero fret is often found on cheaper instruments, as it's much easier to set up an instrument this way; to make a proper nut requires that each string notch be carefully cut to the proper depth so that the string is neither too high, affecting overall string height and intonation of fretted notes—nor too low, which makes a plucked or picked string buzz against the frets. With a zero fret, the fret merely needs to be the right height. However, a zero fret also makes the sound of the open string similar to fretted notes. A conventional nut makes the open string sound slightly different—and for this reason some high-end instruments use a zero fret.
- Some fretted instruments have a compensated nut. This type of nut provides better intonation across the instrument. The principle: given that strings are different thicknesses and have different tensions, the temperament of each fret is not 100% accurate for an equal temperament instrument. This is especially evident on the first few frets of an electric guitar. Many guitar players notice how 'open position' chords (Such as E, A, C, D and G) never sound in tune with each other. A compensated nut aims to correct this, by staggering the starting position of each string according to thickness. While not a complete solution such as a true temperament fretboard, there is a noticeable difference in tuning within chords. Many guitar companies, such as Music Man, and ESP include compensated nuts as standard on most of their instruments, and companies such as Earvana provide retrofittable types.
- Another type is a locking nut. This nut, usually used in conjunction with a locking vibrato system such as a Floyd Rose or Kahler, clamps the string before the node point. This greatly improves tuning stability when using the vibrato bar. A drawback however, is that the locking nut must be loosened using an Allen wrench to tune outside the range of the fine tuners on the bridge (if present).
- The erhu does not use a hard nut to define the vibrating length of the open string, but rather a qiān jin (千斤) : a loop of string, or, less commonly, a metal hook.
- Some guitars have a rolling nut. This is design made popular by Fender where the strings sit on roller bearings instead of nut slot. The rollers allow the string to freely slide or roll through the nut. The roller nut is designed keep the guitar in tune by not allowing the strings to get stuck in the nut.