Ten Minute Master No165

Guitar setup and intonationCorrectly setting up a guitar can transform the instrument’s performance. Grant Bridgeman puts down his pick.

T he last time many guitars were correctly set up and playing at their best was when they were originally

purchased – little will have been done to the average guitar throughout its working life. But good and regular maintenance will improve its playability, sound and tuning, transforming what may be a bit of a plank into an instrument that’s a pleasure to play.

Strung outAll guitars, whether electric, acoustic or classical, operate fundamentally on similar principles. The difference in the case of electric guitars and other instruments that have a pickup are that the vibrations of the strings are sensed and subsequently amplifi ed

harmonics and defi nes the pitch of the note itself. The frequencies and amplitudes of the other harmonics are dependent on a range of other factors, most predominantly the position at which the string is plucked.

A ‘node’ is a point of zero displacement on the vibrating string, and they exist for each wavelength within the harmonic

series above the fundamental. When a string is plucked at a node, the corresponding harmonic frequency is not excited, so the overall harmonic content is altered. This is one of the reasons behind the tonal variation that can be heard when strings are plucked closer to the bridge or closer to the fretboard. Other factors are the rigidity of the pick and the characteristics of the string.

Keeping it realGuitarists will be familiar with the term ‘harmonics’, identifying the word with the technique of playing at specifi c points on the fretboard (both open and fretted). But this technique is more accurately referred to as ‘artifi cial harmonics’, since playing in this way produces just one of the selected harmonic series while muting the fundamental, which is usually the

predominant sound. The artifi cial harmonic located above the 12th fret is the fi rst harmonic for the open string (the string vibrates in two equal lengths exactly one octave above the fundamental). It is this property that can be used to check the intonation of the guitar.

The term ‘intonation’ describes the tuning of the guitar along the fretboard. Intonation is said to be

correct when the entire fret range is in tune in relation to the open string. To check it, compare the pitch of the artifi cial harmonic at the 12th fret with the pitch of the fretted note at the 12th fret. The intonation relates to the scale length of each string, which is adjusted at the saddle. Changing the string length will adjust the pitch of the fretted note.

Each string has to be adjusted separately while tuned to concert pitch (A=440Hz). When the pitch of the fretted note is higher than the harmonic, the length of the vibrating string needs to be lengthened; conversely, when the pitch of the fretted note is lower than the harmonic, the length of the string needs to be shortened.

Adjusting the string length will alter the tension in the string and therefore the pitch, so it is necessary to constantly retune the

Regular maintenance can dramatically improve a guitar’s playability and sound.

electronically, rather than the body of the instrument acoustically amplifying the vibrations.

Strings are a very visual medium and can help you to understand some of the basics of harmonics and overtones as well as what goes into building up tonal character. When a fi xed string vibrates, a number of frequencies combine to form the overall tone

of a note. The fi rst harmonic is the vibrating length of the string, which on a guitar corresponds to the distance between the fretted note and the bridge. As the fundamental frequency, it has the largest amplitude of all the string

This Gibson-style bridge allows for easy adjustment of the length of the individual strings.

Setting up the intonation correctly, therefore, is a relatively easy job.

Guitar pickups such as this

humbucker from Seymour

Duncan have pole pieces

that can be individually

adjusted for height.

www.musictechmag.co.uk38 December 2009 MusicTech MAGAZINE

Ten Minute Master No165 Guitar setup & intonation

string before checking the intonation. If your guitar is regularly detuned or you use alternative tunings, it is worth checking the intonation for these pitches as there will be slight differences in the setup.

Fret talkWhen checking intonation, another problem often becomes apparent: fret buzz. This is when the string vibrates against a fret higher up the fretboard. In minor cases it is literally a light buzz that often goes unnoticed or is of little concern during ‘normal’ playing, but in more serious cases the note can actually ‘choke out’, resulting in the note having reduced sustain or not sounding at all.

The problem is caused by a combination of the playing height of the string, the frets themselves and the string gauge. String height can be increased at the bridge, usually via an adjustable

mechanism in the case of electric guitars (it is generally possible to adjust the height of each string individually) or by placing thin shim pieces under the saddle of classical and acoustic guitars. If the guitar has a single moulded bridge piece it is probably worth having it set up by a professional as the saddles are often glued in place and can be tricky to remove (it is vital to replace the saddle in the correct orientation as it will be pre-shaped to allow for different string sizes).

A player’s preferred action is a very personal thing and comprises a combination of the guitar, the guitarist and their style of playing. A high action results in the guitar being harder to play, but also means increased volume and a reduction in fret buzz, but it’s ideal for slide guitar playing. With a higher action it is possible to use heavier-gauge strings, which can give a warmer, fuller tone to the

FURTHER INFO■ The Seymour Duncan website

is a good source of information. This page explores common wiring techniques for different pickup and switch combinations. www.seymourduncan.com/support/wiring-diagrams

■ The Project Guitar website is an excellent reference source for anyone maintaining an electric guitar (or, indeed, building one from scratch).

■ Erik Jansson’s Acoustics For Violin And Guitar Makers covers much of the theory about the nature of string sounds. www.speech.kth.se/music/acviguit4/part4.pdf

guitar. On electric guitars, a lower action is usually preferable as it makes the guitar somewhat easier to play, especially for lead guitar work, which necessitates lighter string gauges that allow for easier string bends. The cost is a thinner tonal quality (which is often actually desired) and less volume, but because the guitar is amplified this is not usually an issue.

Pick it upThe pickups on electric guitars work by sensing the vibrations of the string and converting them into an electrical signal. However, the exact mechanisms vary slightly between different styles of pickup, with the resulting sound being quite different. The conventional pickup resides within the body of the electric guitar underneath the strings and is positioned in relation to the string harmonics. A pickup that’s close to the bridge will emphasise the shorter wavelengths in the harmonic series, giving a brighter tone. Positioning them nearer the fretboard emphasises the longer wavelength harmonics, giving a more mellow tone.

The pickup itself operates on a similar principle as dynamic microphones – electrical induction. The ‘pole piece’ within the pickup is a magnet that generates a magnetic field around both the string and the pickup coil, which is wound around the lower section of the pole pies. As the metal string vibrates it causes variations within the magnetic field; these change within the field then induce a current within the pickup coils. It is this signal that is output to the amplifier.

The proximity of the magnet to the string has both benefits and drawbacks. Locating the magnet closer to the string increases the

Harmonic modes are generated as the string vibrates at its fundamental frequency (first

harmonic). The second harmonic is half the length and so on.

strength of the magnetic field around the string, therefore the variations in the field caused by the moving string create a stronger induced current – and hence a louder signal. The problem with having the string closer to the magnet, though, is that the magnetic field below the string pulls it towards the pole piece and dampens the string’s vibrations, resulting in less sustain and, in the most serious of cases, choking out completely.

The sheer joy of a well-set up guitar can transform something that is a bit of a plank into a perfectly decent instrument that’s far more inspiring and comfortable to play. That’s certainly time and money well spent... MTM

Tech Terms■ Impedance

The output signal of an electric guitar is at quite a low level, so care needs to be taken to ensure that the destination input impedance is suitable for the output impedance of the guitar. Generally speaking, the higher the input impedance the better – ideally in the region of megohms, hence the need to run it through a DI box rather than plugging directly into a mixing desk.

■ Anti-node The node of a waveform is the point of zero displacement; the anti-node is the point of maximum displacement from the resting position.

■ Piezoelectric pickups Piezoelectric pickups are small contact microphones that sense the vibrations within the body of an instrument and convert them into an electrical signal. They’re often placed under the bridge or saddle of a guitar and offer an alternative to conventional mic’ing.

Artificial harmonics exist at multiple points along the fretboard. They can be played by plucking the string while very lightly fretting at the

points highlighted and are vital for the tasks of checking and correctly setting intonation.

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