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The Electric Guitar
From Wikipedia, the free encyclopedia
History | Tunings | Pickups | Simple Sound Physics Related Specifically to the Guitar | Acoustically Important Construction Features
The electric guitar is used extensively in many popular styles of music, including almost all genres of rock and roll, country music, pop music, jazz, blues, and even contemporary classical music. Its distinctive sound and intimate association with many legendary internationally-famous musicians has made it the signature instrument of late twentieth-century music. Specialised steel guitars, although they are also electric instruments descended from the guitar, are normally not considered electric guitars but rather as a separate instrument. This distinction has important consequences on claims of priority in the history of the electric guitar.
Both the North America-built Godin LG (left) and the Squier Stratocaster (right) are solid-body electric guitars, but they differ significantly in design, including scale length, neck woods, body woods, and pickup type.There are three main types of electric guitar:
Hollow body electric guitar
Electric acoustic guitar
Solid body guitar
Electric acoustic guitars
Some steel-string acoustic guitars are fitted with pickups purely as an alternative to using a separate microphone. These are called electric acoustic guitars, and are regarded as acoustic guitars rather than electric guitars. These should not be confused with hollow body electric guitars, which are more of electric guitars fitted with hollow sound chambers.
Although rare, the one-string guitar is sometimes heard, particularly in Delta blues, where improvised folk instuments were popular in the 1930s and 1940s. Eddie "One String" Jones had some regional success with a version of "Rolling and Tumbling Blues" on a single string with a pickup. In a more contemporary style, Little Willie Joe, the inventor the Unitar had a considerable rhythm and blues instrumental hit in the 1950s with "Twitchy", recorded with the Rene Hall Orchestra.
The best known four-string guitar player is Tiny Grimes, who played on 52d street with the beboppers and played a major role in the Prestige Blues Swingers. Grimes' guitar omitted the bottom two strings.
Seven-string guitars exist, most of which add a low B string below the E. They were popularized by Steve Vai and others in the 1980s, and have been recently revived by some nu metal bands (such as Korn). Jazz guitarists using a seven-string include veteran jazz guitarist Bucky Pizzarelli and his son John Pizzarelli. The seven-string guitar has also played an essential role in progressive rock, and is commonly used in bands such as Dream Theater and by experimental guitarists such as Ben Levin. Another common seven-string arrangement is a second G string situated beside the standard G string and tuned an octave higher, in the same manner as a twelve-stringed guitar (see below).
Eight-string electric guitars are rare but exist, such as the one played by Charlie Hunter (manufactured by Novax Guitars), but they are extremely unusual. The largest manufacturer of 8- to 14-strings is Warr Guitars. Their models are used by Trey Gunn (of King Crimson) who has his own signature line from the company.
Twelve-string guitarsTwelve string electric guitars feature six pairs of strings, usually with each pair tuned to the same note. The extra E, A, D, and G strings add a note one octave above, and the extra B and E strings are in unison. The pairs of strings are played together as one, so the technique and tuning are the same as a conventional guitar, although creating a much fuller tone. They are used almost solely to play chords and are relatively common in folk rock music.
Double neck guitarsDdouble-neck (or, less commonly, "twin-neck") guitars enable guitarists to play guitar and bass guitar or, more commonly, a six-string and twelve-string. Jimmy Page's use of a custom-made Gibson 6-string and 12-string guitar, to enable him to replicate his use of two different guitars when performing Led Zeppelin's song "Stairway to Heaven" in a concert setting, brought double-necked guitars into the public eye.
English progressive rock bands such as Genesis used custom made instruments produced by the Shergold company. Rick Nielsen, guitarist for Cheap Trick, uses a variety of custom guitars, many of which have five necks, with the strap attached to the body by a swivel so that the guitar can be rotated to put any neck into playing position. Guitar virtuoso Steve Vai occasionally uses a triple-neck guitar; one neck is twelve string, one is six string and the third is a fretless six string. Claudio Sanchez of Coheed & Cambria uses a double neck guitar on the song Welcome Home.
Adolph Rickenbacker invented the electric guitar. The popularity of the electric guitar began with the big band era because amplified instruments became necessary to compete with the loud volumes of the large brass sections common to jazz orchestras of the thirties and forties. Initially, electric guitars consisted primarily of hollow archtop acoustic guitar bodies to which electromagnetic transducers had been attached.
Sketch of Rickenbacker "frying pan" lap steel guitar from 1937 patent application.Electric guitars were originally designed by an assortment of luthiers, electronics enthusiasts, and instrument manufacturers, in varying combinations. Some of the earliest electric guitars, then essentially adapted hollow bodied acoustic instruments, used tungsten pickups and were manufactured in the 1930s by Rickenbacker. In 1935, a Soviet scientist working separately from his western colleagues was known to have produced an electric Russian guitar called the "Kuznetsov electromagnetic guitar". It was exhibited at a technology expo in Moscow, but its development was halted since the Stalin regime was hostile to guitar music.
The first recording of an electric guitar was by jazz guitarist Eddie Durham in 1937. Durham introduced the instrument to a young Charlie Christian, who made the instrument famous in his all-too-brief life and is generally known as the first electric guitarist and a major influence on jazz guitarists for decades thereafter.
The version of the instrument that is best known today is the [solid body] electric guitar, a guitar made of solid wood, without resonating airspaces within it.
At least one company, Audiovox, built and may have offered an electric solid-body as early as the mid-1930s. Rickenbacher, later spelled Rickenbacker (both are pronounced Rickenbocker) offered a cast aluminum electric guitar, nicknamed "The Frying Pan" or "The Pancake Guitar", beginning in 1933, which reportedly sounded quite modern and aggressive when tested by vintage guitar researcher John Teagle.
Another early solid body electric guitar was designed and built by musician and inventor Les Paul in the early 1940s, working after hours in the Gibson Guitar factory. His "log" guitar (so called because it consisted of a simple 4x4 wood post with a neck attached to it and homemade pickups and hardware, with two detachable Swedish hollow body halves attached to the sides for appearance only) was patented and is often considered to be the first of its kind, although it shares nothing in design or hardware with the solid body "Les Paul" model sold by Gibson.
Sketch of Fender lap steel guitar from 1944 patent application.In 1950 and 1951, electronics and instrument amplifier maker Clarence Leonidas Fender - better known as Leo Fender - through his eponymous company, designed the first commercially successful solid-body electric guitar with a single magnetic pickup, which was initially named the "Esquire". The two-pickup version of the Esquire was called the "Broadcaster". However, Gretsch had a drumset marketed with a similar name (Broadkaster), so Fender changed the name to "Telecaster" in homage to the new phenomenon of television. Features of the Telecaster included: an ash body; a maple 25½" scale, 21-fret neck attached to the body with four-bolts reinforced by a steel neckplate; two single-coil, 6-pole pickups (bridge and neck positions) with tone and volume knobs, pickup selector switch; and an output jack mounted on the side of the body. A black bakelite pickguard concealed body routings for pickups and wiring. The bolt-on neck was consistent with Leo Fender's belief that the instrument design should be modular to allow cost-effective and consistent manufacture and assembly, as well as simple repair or replacement. Due to the earlier mentioned trademark issue, the earliest Telecasters were delivered with headstock decals with the Fender logo but no model identification, and are commonly referred to by collectors as "Nocasters".
In 1954, Fender introduced the Fender Stratocaster, or "Strat". It was positioned as a deluxe model and offered various product improvements and innovations over the Telecaster. These innovations included an ash or alder double-cutaway body design for badge assembly with an integrated vibrato mechanism (called a synchronized tremolo by Fender, thus beginning a confusion of the terms that still continues), three single-coil pickups, and body comfort contours. Leo Fender is also credited with developing the first commercially-successful electric bass called the Fender Precision Bass, introduced in 1951.
GibsonLes Paul with his "log" solid body electric guitar.Gibson, like many guitar manufacturers, had long offered semi-acoustic guitars with pickups, and previously rejected Les Paul and his "log" electric in the 1940s. In apparent response to the Telecaster, Gibson introduced the first Gibson Les Paul solid body guitar in 1952 (although Les Paul was actually brought in only towards the end of the design process for expert fine tuning of the nearly complete design and for marketing endorsement ). Features of the Les Paul include a mahogany body with a carved maple top (much like a violin) and contrasting edge binding, two single-coil "soapbar" pickups, a 24¾" scale mahogany neck with a more traditional glued-in "set" neck joint, binding on the edges of the fretboard, and a tilt-back headstock with three tuners to a side. The earliest models had a combination bridge and trapeze-tailpiece design that was in fact designed by Les Paul himself, but was largely disliked and discontinued after the first year. Gibson then developed the Tune-o-matic bridge and separate stop tailpiece, an adjustable non-vibrato design that has endured. By 1957, Gibson had made the final major change to the Les Paul as we know it today - the humbucking pickup, or humbucker. The humbucker, invented by Seth Lover, was a dual-coil pickup which featured two windings connected out of phase and reverse-wound, in order to cancel the 60-cycle hum associated with single-coil pickups; as a byproduct, however, it also produces a distinctive, more "mellow" tone which appeals to many guitarists. The more traditionally designed and styled Gibson solid-body instruments were a contrast to Leo Fender's modular designs, with the most notable differentiator being the method of neck attachment and the scale of the neck (Gibson-24.75", Fender-25.5"). Each design has its own merits. To this day, the basic design of many solid-body electric guitar available today are derived from the original designs - the Telecaster, Stratocaster and the Les Paul.
As its name implies standard tuning is by far the most popular tuning on a 6-string guitar, it comprises the following note arrangement.
String Note Frequency
1 (thinnest) e' 329.6 Hz
2 b 246.9 Hz
3 g 196.0 Hz
4 d 146.8 Hz
5 A 110.0 Hz
6 (thickest) E 82.4 Hz
[Note: The guitar is a transposing instrument. Its pitch sounds one octave lower than it is notated, the pitches referred to above are referenced standard pitch (a' = 440hz)].
This pattern can also be denoted as E-A-d-g-b-e'. (See note for an explanation of the various symbols used in the above table and elsewhere in this article.)
Standard tuning has evolved to provide a good compromise between simple fingering for many chords and the ability to play common scales with minimal left hand movement.
The separation of the first (e') and second (b) string, as well as the separation between the third (g), fourth (d), fifth (A), and sixth (E) strings by a 5-semitone interval (a perfect fourth) allows notes of the chromatic scale to be played with each of the four fingers of the left hand controlling one of the first four frets (index finger on fret 1, little finger on fret 4, etc.). It also yields a symmetry and intelligibility to fingering patterns.
The separation of the second (b), and third (g) string is by a 4-semitone interval (a major third). Though this breaks the fingering pattern of the chromatic scale and thus the symmetry, it eases the playing of some often-used chords and scale, and it provides more diversity in fingering possibilities.
Alternate tuning refers to any open string note arrangement other than that of standard tuning detailed above. Despite the usefulness and almost universal acceptance of standard tuning, many guitarists employ such alternate tuning arrangements in order to exploit the unique chord voicing and sonorities that result from them. Most alternate tunings necessarily change the chord shapes associated with standard tuning, which results in certain chords becoming much easier to play while others may become impossible to play.
Rock music tunings
Guitar tunings in rock music and metal mainly aim at making power chords much simpler to play.
Dropped D: D-A-d-g-b-e'
This tuning is not only used by metal and rock bands, but also folk musicians. It allows power chords (also known as fifth chords) to be played with a single finger on the lowest three strings. It is also used extensively in classical guitar music and transcriptions since it allows the lower open strings to sound the root and fifth of the D major scale as part of the bassline.Some guitarists choose to use a capo on the 2nd fret with this tuning so that they can retain the ease of playing power chords without the darker sound created by the D tuning. Examples of this include the band Angels and Airwaves and Billy Talent.
Dropped C: C-G-c-f-a-d'
This tuning is the same as dropped D, but each string is lowered an additional whole step, or 2 semitones. Technically a "drop C" tuning would be C-A-D-G-B-e. However, the tuning technically known as "Dropped D tuned down 1 whole step" is commonly referred to as "Dropped C" tuning, as very few people drop only the sixth string (although Zakk Wylde has been known to occasionally drop only the sixth string in tuning). This gives the guitar a very low and heavy sound, and usually requires extra-thick strings to maintain tension. This tuning is frequently used by rock bands, such as Godsmack, Thrice, Mudvayne, Bullet For My Valentine, Dethklok and System of a Down, as well as various metalcore bands, such as Atreyu, As I Lay Dying, and It Dies Today, to achieve the lowest sound possible. Tuning a standard, non-baritone guitar any lower than this is difficult.
Dropped B: B-F#-B-e-g#-c#'
This tuning is the same as dropped D & C, but lowered from dropped C an additional semitone, or half step. This tuning is very popular with nu-metal act Slipknot, metalcore act Bleeding Through, and other alternative metal/post-grunge bands. Very heavy gauge strings are required for this tuning.
Dropped A: A-E-A-d-f#-b'
A very low drop tuning used very rarely in metal and death metal bands. Death metal band Nile is known to use this tuning. Another variation of this tuning is A-A-D-G-B-e used by The Melvins and Foo Fighters on a few songs.
"Hardcore" Tuning: C-G-c-f-a-a#'
A rather uncommon tuning, "hardcore" tuning is used by bands of hardcore, grindcore, and even some metalcore. It much resembles dropped C tuning, except for the two bottom strings, which, depending on what is most useful for the guitarist, are tuned one semitone (a minor second) apart. This allows the guitarist to easily create the very harsh dissonance of the minor second. It is often used by Norma Jean, Drop Dead, Gorgeous, The Devil Wears Prada, Fear Before The March Of Flames, The Locust, and The Bled,and Sinai Beach to name but a few.
E-flat Tuning: Eb-Ab-db-gb-bb-eb'
This tuning is achieved when all the strings are flattened by a half step. Bands that use or have used this include Taking Back Sunday, Guns N' Roses, Led Zeppelin, Coheed and Cambria, Brand New, Weezer, Nirvana, Stevie Ray Vaughan, The Smashing Pumpkins, Iced Earth, Green Day, Eskimo Joe, Jimi Hendrix, KISS and Van Halen. This can be combined with other tuning techniques such as dropped D tuning and makes no difference to fingering. Often the key will be considered by the players as if played in standard tuning. This tuning can be used for a number of reasons: to make larger strings bend more easily, to make the tone heavier, to better suit the vocalist's range, to play with saxophone family more easily, or to play in Eb pentatonic minor formed by the black keys of a keyboard. Heavier bands may tune down to D, C#, or even C. B is possible but sometimes seven string guitars are used instead.
A common reasoning to be considered in downtuned guitars is that generally, the lower the notes associated with that tuning, the "muddier" aka "less focused" that guitar sounds. Many bands/guitarists try to "mask" the sound by using other strategies, but in the end, all general problems lead to the same main idea: you can't hide a note. It is to be considered that many contemporary rock/metal bands associate the tuning with exploiting the lowest chords possible. This has been widely recognized at the dawning of metal/music, but gained much more "momentum" in the strengthening of Metallica's heyday.
Classical guitar tunings
The classical guitar developed over a period of 500 years and a number of guitar tunings are commonly used this genre, some based upon historical practice. Unlike other musical styles, in which alternate tunings are used by artists largely as a matter of individual preference, in classical guitar styles, the decision to employ alternate tunings such as this largely resides with composers or (more usually) arrangers of musical transcriptions. Thus, classical guitarists performing known transcriptions are assumed to be using defined tunings.
Renaissance lute tuning: E-A-d-f#-b-e'
This tuning may also be used with a capo at the third fret to match the common lute pitch: G-c-f-a-d'-g'. This tuning also matches standard vihuela tuning and is often employed in classical guitar transcriptions of music written for those instruments.
"Pseudo Russian" or "g" tuning: D-G-d-g-b-e'
A versatile tuning examples of which can be heard in Choro de Saudade by Agustín Barrios and also in well known transcriptions of La Maja de Goya by Enrique Granados and Sevilla by Isaac Albéniz.
Various other scordatura have been utilised by composers and players, dependent on the demands of the music, for example Fernando Sor wrote pieces for the sixth string tuned to F and the twentieth century player John Williams tuned his fifth string to B for his transcription of Granada by Isaac Albéniz, recorded in 1980.
An open tuning is a type of guitar tuning in which the open strings are tuned to form a common chord (usually major) which can be 'transposed' to any higher pitch simply by placing a finger across all of the strings at any chosen fret. Blues slide guitarists often take advantage of this effect, whereas fingerstyle guitarists tend to use various combinations of the open strings to provide a sustained chordal accompaniment to melodies played on fretted higher strings.
Open G: D-G-d-g-b-d'
This tuning is commonly used for blues, or slide guitar. In classical guitar this is sometimes referred to as the dropped G tuning. It retains the relationship of the fourth between the two lower strings. This is also known as 'bluegrass guitar' tuning.
Open D: D-A-d-f#-a-d'
Open E: E-B-e-g#-b-e'
Open A: E-A-e-a-c#'-e'
Open C: C-G-c-g-c'-e'
Open D minor: D-A-d-f-a-d'
This is commonly used for squareneck resonator guitars. The lack of a low D means that a complete strum does not have the same harmonic strength that the Open G has.
All fourths: E-A-d-g-c'-f'
This tuning is like that of the lowest four strings in standard tuning. It removes from standard tuning the irregularity of the interval of a third between the second and third strings. With regular tunings like this, chords can simply be moved down or across the fretboard, dramatically reducing the number of different finger positions that need to be memorized. The disadvantage is that not all major and minor chords can be played with all six strings at once.
All fifths: C-G-d-a-e'-b'
This is a tuning in intervals of fifths like that of a mandolin or a violin. Has a remarkably wide range, though it is difficult to achieve (the high b" makes the first string very taut such that it will break easily), and may not play well on an acoustic guitar (the low C is too low to resonate properly in a standard guitar's body).
Robert Fripp's "New Standard Tuning": C-G-d-a-e'-g'
This is a devised by Robert Fripp of King Crimson, used by most Guitar Craft students around the world. The tuning is similar to all fifths except the first string is dropped from b' to g'. Some guitarists maintain that the term 'New Standard Tuning' is a misnomer and consider it to be a source of controversy, but the name appears to have stuck due the absence of viable alternative designations. Time will tell whether the tuning is in fact accepted outside of GC as a viable all-purpose tuning.
Popularised by Davey Graham after having been inspired by Arabic oud tuning while living in Morocco, DADGAD tuning is now frequently used in Celtic music, and by artists such as Neil Young, Jimmy Page, Pierre Bensusan, Soig Siberil and Paul McSherry.
Major third guitar tuning: E-G#-c-e-g#-c'
This tuning devised in 1960s by jazz guitarist Ralph Patt.
Orkney tuning: C-G-d-g-c'-d'
It is a wonderful tool for melodic (non-linear) playing, in which you avoid playing subsequent notes on the same string.
This is achieved on a high-strung guitar - a guitar strung with only the high strings of a 12-string guitar set. This is known as "Nashville tuning" when the strings are in standard tuning.
G tuning G-c-f-b♭-d'-g'
Some guitar manufacturers recommend all six strings of their mini-scaled (3/4 and 1/2) guitar models (Epiphone Flying Vee-Wee, for example) be tuned one and a half steps or a minor-third higher than standard tuning. This is primarily intended to keep good tuning stability of those short-scaled guitars with the tension of strings close to that of the original strings design. For example, a 1/2 scale Johnson mini-Strat type guitar has a scale length of 20.75 inches, about 18% shorter than that of a regular Strat's 25.5 inches, requiring about the same magnitude of less tension on strings in order to produce the same pitches with the same string gauges, which often could result in a significant tuning stability problem. Unlike other alternative tunings, this tuning maintains the relative pitches or intervals of standard tuning between strings so that it only requires simple transposing for playing any score.
Ostrich guitar tuning D-d-d-d-d'-d'
A tuning pioneered by Lou Reed in which all strings are tuned to D.
12-string guitar tuning used in traditinal Swedish folk music A (one octav below regular)-D (one octave below regular)-A-D-a-d
This tuning was pioneered by Roger Tallroth, a guitarist and folk musician from Sweden. By using thick nylon strings (for tenor guitar) on the low A and low D (tuned unison), it creates a very fat bass guitar sound to the 12-string guitar and i suited to play a lot of bass walkings. The tuning is widely used in Sweden for playing traditional Swedish folk music.
DADADF Very similar to open D minor.
Complete range of string pitch combinations
Each of the six strings can be alternately tuned as low as a whole step lower and as much as a whole step higher without stressing the neck or the strings. With five possible tunings for each string (+2, +1, 0, -1, and -2), there can be as many as 15,625 possible tunings for a six-string guitar. Note that a standard guitar sounds one octave below pitch as written in standard notation. That is, the first string in standard tuning plays the E note that is a major third above middle C, and is written on the staff as a major tenth above middle C.
There are also tenor guitars, baritone guitars tuned BEADF#B (or ADGCEA, GDGCDG, GDGCEA, GCGCEG, etc.) a fourth lower than a standard (prime) guitar, treble guitars tuned a fourth higher than a prime guitar and contrabass guitars, which are tuned one octave lower than prime guitars. Seven string guitars have an extra low string which is a B in standard tuning.
A magnetic pickup consists of a permanent magnet wrapped with a coil of a few thousand turns of fine copper wire. The pickup is most often mounted on the body of the instrument, but can be attached to the neck and/or pickguard, as on many electro-acoustic archtop jazz guitars. The vibration of the nearby soft-magnetic strings modulates the magnetic flux linking the coil, thereby inducing an alternating voltage through the coil of wire. This signal is then carried to amplification or recording equipment via a cable (or by radio transmission). There may also be an internal preamplifier stage between the pickup and cable. More generally, the pickup operation can be described using the concept of a magnetic circuit. In this description, the motion of the string varies the magnetic reluctance in the circuit created by the permanent magnet.
The output voltage of pickups varies between 100 mV rms to over 1 V rms for some of the higher output types. Some high-output pickups achieve this by employing very strong magnets thus creating more flux and thereby more output. These can be detrimental to the final sound because the magnets can tend to attract the strings and damp them thus greatly reducing sustain. Other high-output pickups have more turns of wire to increase the voltage generated by the string's movement. However, this also increases the pickup's output resistance/impedance, which can affect high frequencies if the pickup is not isolated by a buffer amplifier.
The turns of wire in close proximity to each other have an equivalent self-capacitance which, when added to any cable capacitance present, resonates with the inductance of the winding. This resonance can accentuate certain frequencies, giving the pickup a characteristic tonal quality. The more turns of wire in the winding, the higher the output voltage but the lower this resonant frequency. The inductive source impedance inherent in this type of transducer makes it less linear than other forms of pickups, such as piezo-electric or optical. The tonal quality produced by this nonlinearity is, however, subject to taste, and may therefore also be considered by some to be aesthetically superior to that of a more linear transducer.
The external load usually consists of resistance (the volume and tone potentiometer in the guitar, and any resistance to ground at the amplifier input) and capacitance between the hot lead and shield in the guitar cable. The cable capacitance has a large effect and must not be neglected. This arrangement of passive components forms a resistively-damped second-order low-pass filter. Electromagnetic pickups are usually designed to feed a high input impedance, typically a megaohm or more and a low impedance load will reduce the high-frequency response of the pickup because of the filtering effect of the inductance.
PRS's Dragon humbuckerOne problem with electromagnetic pickups is that — along with the musical signal — they also pick up mains hum. Mains hum consists of a fundamental signal at a nominal 50 or 60 Hz, depending on local alternating current frequency, and usually some harmonic content. The changing magnetic flux caused by the mains current links with the windings of the pickup, inducing a voltage by transformer action.
To overcome this effect, the humbucking pickup was developed, originally by Seth Lover of Gibson. A humbucking pickup, shown in the image at the top of this page, generally comprises two standard pickups wired together with identical coils of opposite polarity and with identical magnets also opposed in polarity. Any ambient magnetic noise, such as hum from power-supply transformers, will induce in each coil a voltage of equal magnitude but opposite sign or direction, so that these two voltages (-V + V) cancel each other when combined -- the pickup "bucks hum." However, the vibrating steel strings disturb both magnetic fields, and because the fields point in opposite directions, they induce opposite voltages in the two coils. These two coils, as previously stated, are also "out of phase," so the signal induced by the magnet of opposite polarity in the coil of opposite polarity is "in phase" with the signal from the other magnet and coil: (-1)(-1) = 1.
A side-effect of this technique is that, when wired in series, as is most common, the overall inductance of the pickup is increased, which lowers its resonant frequency and attenuates the higher frequencies, giving a fatter and less trebly tone than either of the two component single-coil pickups would give singly. This is the essence of the "humbucker tone."
With a notable exception of rail pickups, pickups have magnetic polepieces — one or two for each string. These polepiece centers should be perfectly aligned with strings, or else sound will be suboptimal as pickup would capture only a part of vibrational energy.
String spacing is not even on most guitars: it starts with minimal spacing at nut and ends with maximal at bridge. So, bridge, neck and middle pickups should have a different polepiece spacing on the same guitar.
There are several standards on pickup sizes and string spacing between the poles. Spacing is measured either as a distance between 1st to 6th polepieces' centers (this is also called "E-to-E" spacing), or as a distance between adjacent polepieces' centers. (Photo: compliments www.guitargai.com)
(Vintage Gibson guitars) 1.90"
48 mm 0.380"
(Most Fender guitars, modern Gibson, Floyd Rose bridges) 2.01"
51 mm 0.402"
Very close to bridge, extra pickup
(Roland guitar synth hex pickups) 2.060"
52.3 mm 0.412"
(Fender Telecaster guitars) 2.165"
55 mm 0.433"
Usually an electric guitar has more than one magnetic pickup. A combination of pickups is called a pickup configuration. It is usually notated by just writing out the pickup types, using "S" for single-coil and "H" for humbucker, in order from neck pickup to bridge pickup. Popular pickup configurations include:
S-S (Fender Telecaster)
S-S-S (Fender Stratocaster)
H-H (Gibson Les Paul)
S-S-H (Fender Fat Stratocaster)
Less frequently found configurations are:
S (Fender Esquire)
H (Gibson Les Paul Junior)
H-H-H (Some Gibson Les Paul Gold Tops and Customs)
A piezoelectric pickup on a classical guitar.More recently, many semi-acoustic and acoustic guitars, and some electric guitars and basses, have been fitted with piezoelectric pickups instead of, or in addition to, magnetic pickups. These have a very different sound which some prefer, and also have the advantage of not picking up unwanted magnetic fields, such as mains hum and feedback from hearing-aid loops.
Piezoelectric pickups have a very high output impedance and appear as a capacitance in series with a voltage source. They must therefore have an instrument-mounted buffer amplifier fitted if the sound is to retain its full frequency response. Piezo pickups are usually mounted under the bridge and sometimes form part of the bridge assembly itself.
The piezo pickup gives a very wide frequency range output compared to the magnetic types and can give large amplitude signals from the strings. For this reason, it is usually necessary to run the buffer amplifier from relatively high voltage rails (about ±9 V) to avoid distortion due to clipping. Some musicians prefer a preamp that isn't as linear (like a single-FET amplifier) so that the clipping is "softer", although such an amplifier starts to distort sooner, this makes the distortion less "buzzy" and less audible than a more linear, but less forgiving op-amp . However, at least one study  indicates that most people can't tell the difference between FET and op-amp circuits in blind listening comparisons of electric instrument preamps, a finding which correlates with results of formal studies done in other types of audio devices. Sometimes, piezoelectric pickups are used in conjunction with magnetic types to give a wider range of available sounds.
For early pick-up devices using the piezoelectric effect, see phonograph.
Hexaphonic pickups (also called divided pickups and polyphonic pickups) have a separate output for each string (Hexaphonic assumes six strings, as on a guitar). This allows for separate processing and amplification for each string. It also allows a converter to sense the pitch coming from individual string signals for producing note commands, typically according to the MIDI (musical instrument digital interface) protocol. A hexaphonic pickup and a converter are usually components of a guitar/synthesizer.
Such pickups are relatively uncommon (compared to normal ones), and only a few notable models exists. Hexaphonic pickups can be either electromagnetic or piezoelectric.
Roland GK-2 (single coil) and GK-2a (humbucking) are one of the most famous models, factory-installed on many guitars. Compatible with popular Roland GR series of guitar synthesizers.
Copeland Hex (by Rick Copeland). 
Zeta Strados (violin) 
Barbera transducers (violin) 
RMC Acoustic Gold pickup saddles & Poly-Drive II remote preamp (for acoustic guitar) 
RMC Acoustic Gold pickup saddles & Poly-Drive IV onboard preamp (for acoustic guitar) 
RMC Pow'r Bridge G pickup saddles (tune-o-matic) & Poly-Drive 1 onboard preamp (for electric guitar) 
RMC Pow'r Bridge ST pickup saddles (strat-style) & Poly-Drive 1 onboard preamp (for electric guitar) 
RMC Pow'r Bridge W pickup saddles (wilkinson) & Poly-Drive 1 onboard preamp (for electric guitar) 
Ghost Bass Bridge 
Optical pickups are a fairly recent development that work by sensing the interruption of a light beam by the string. The light source is usually an LED, and the detector is a photodiode or phototransistor. These pickups have complete insensitivity to magnetic or electric interference and also have a very wide and flat frequency response unlike magnetic pickups.
Optical pickup guitars were first shown at the 1969 NAMM in Chicago, by Ron Hoag 
Active and passive pick-ups
Pick-ups can be either active or passive. Pickups, apart from optical types, are inherently passive transducers. So-called active pickups incorporate electronic circuitry to modify the signal. Passive pick-ups are usually wire wound around a magnet. They can generate electric potential without need for external power, though their output is relatively low, and the harmonic content of output depends greatly on the winding.
Passive pick-ups are very convenient as they require no power source to operate. They are the most popular and widely used pick-up type on electric guitars, and their frequency response curve is unique to the type and manufacturer.
EMG 85 — one of the most famous active pickups in the worldActive pick-ups require an electrical source of energy to operate and include an electronic preamp, active filters, active EQ and other sound-shaping features. They can sometimes give much higher possible output (in comparison to passive) and much flatter frequency response curve. They also are less affected in tone by varying lengths of amplifier lead, and amplifier input characteristics. Magnetic pick-ups used with 'active' circuitry usually feature a lower inductance (and initially lower output) winding that tends to give a flatter frequency response curve.
The disadvantages of active pick-ups are the power source (usually either a battery or phantom power), cost, and less defined unique tonal signature. They are more popular on bass guitars, because of their solid tone; most high-end bass guitars feature an active pick-up. Most piezoelectric and all optical pick-ups are active and include some sort of preamp.
The working principles of electric guitars are primarily based on induced currents and circuits. Magnets are located under each ferromagnetic string, magnetising the strings and causing them to behave as magnets themselves. When a string is played, it oscillates at a certain frequency, causing the magnetic field it creates to oscillate with it. Solenoids (electromagnetic coils) are wrapped around each magnet, giving an induced alternating current at the same frequency. When this travels to an amp, the result is a sound produced at exactly the same pitch as the string.
Tremolo armsDetail of a Squier-made Fender Stratocaster. Note the tremolo arm, the 3 single-coil pickups, the volume and tone knobs.Some electric guitars have a tremolo arm or whammy bar, which is a lever attached to the bridge that can slacken or tighten the strings temporarily, changing the pitch or creating a vibrato. Tremolo properly refers to a quick variation of volume, not pitch; however, the misnaming (probably originating with Leo Fender printing "Synchronized Tremolo" right on the headstock of his original 1954 Stratocaster) is probably too established to change. Eddie Van Halen often uses this feature to embellish his playing, as heard in Van Halen's "Eruption". Early tremolo systems tended to cause the guitar to go out of tune with extended use; an important innovator in this field was Floyd Rose, who introduced one of the first improvements on the vibrato system in many years when in the late 1970s he began to experiment with "locking" nuts and bridges which work to prevent the guitar from detuning even under the most heavy whammy bar acrobatics.
Sound and effects
An acoustic guitar's sound is largely dependent on the vibration of the guitar's body and the air within it; the sound of an electric guitar is largely dependent on a magnetically induced electrical signal, generated by the vibration of metal strings near sensitive pickups. The signal is then "shaped" on its path to the amplifier by using a range of effect devices or circuits that modify the tone and characteristics of the signal.
In the 1960s, guitarists begandistortingsound of the instrument by increasing the gain, or volume, of the preamplifier. This clips the electronic signal and generates harmonics. In the 1960s, the tonal palette of the electric guitar was further modified by introducing an effects box in its signal path. Traditionally built in a small metal chassis with an on/off foot switch, such "stomp boxes" have become as much a part of the instrument for many electric guitarists as the electric guitar itself.
Typical effects include stereo chorus, fuzz, wah-wah and flanging, compression/sustain, delay, reverb, and phase shift. Some important innovators of the heavily effects-altered electric guitar include guitarists such as Frank Zappa, Jimmy Page, Link Wray, Jimi Hendrix, Brian May, Eddie Van Halen, Jerry Garcia, David Gilmour, Pete Townshend Yngwie J. Malmsteen, Steve Vai and Joe Satriani, and technicians such as Roger Mayer.
In the 1970s, as effects pedals proliferated, their sounds were combined with power-tube distortion at lower, more controlled volumes by using power attenuators such as Tom Scholz' Power Soak as well as re-amplified dummy loads such as Eddie Van Halen's use of a variac, power resistor, post-power-tube effects, and a final solid-state amp driving the guitar speakers. A variac is one approach to power-supply based power attenuation, to make the sound of power-tube distortion more practically available.
By the 1980s, and 1990s, digital and software effects became capable of replicating the analog effects used in the past. These new digital effects attempted to model the sound produced by analog effects and tube amps, to varying degrees of quality. There are many free to use guitar effects software for personal computer downloadable from the Internet. By the 2000s, PC with specially-designed sound cards could be used as a digital guitar effects processor. Although digital and software effects offer many advantages, many guitarists still use analog effects.
Some innovations have been made recently in the design of the electric guitar. In 2002, Gibson announced the first digital guitar, which performs analog-to-digital conversion internally. The resulting digital signal is delivered over a standard Ethernet cable, eliminating cable-induced line noise. The guitar also provides independent signal processing for each individual string. Also, in 2003 amp maker Line 6 released the Variax guitar. It differs in some fundamental ways from conventional solid-body electrics. For example it uses piezoelectric pickups instead of the conventional electro-magnetic ones, and has an onboard computer capable of modifying the sound of the guitar to model the sound of many popular guitars.
The electric guitar can be played either solo or with other instruments. It has been used in numerous genres of popular music, as well as (much less frequently) classical music.
Contemporary classical music
While the classical guitar had historically been the only variety of guitar favored by classical composers, in the 1950s a few contemporary classical composers began to use the electric guitar in their compositions. Examples of such works include Karlheinz Stockhausen's Gruppen (1955-1957); Morton Feldman's The Possibility of a New Work for Electric Guitar (1966); George Crumb's Songs, Drones, and Refrains of Death (1968); Hans Werner Henze's Versuch über Schweine (1968); Michael Tippett's The Knot Garden (1966-70); Michael Nyman's opera, Facing Goya (2000); and countless works of Ástor Piazzolla.
In the 1980s and 1990s, a growing number of composers (many of them composer-performers who had grown up playing the instrument in rock bands) began writing for the instrument. These include Steven Mackey, Omar Rodriquez, Lois V Vierk, Tim Brady, John Fitz Rogers, Tristan Murail, Randall Woolf, Scott Johnson and Yngwie Malmsteen with his Concerto Suite for Electric Guitar and Orchestra. The American composers Glenn Branca and Rhys Chatham have written "symphonic" works for large ensembles of electric guitars, in some cases numbering up to 100 players, and the instrument is a core member of the Bang on a Can All-Stars. Still, like many electric and electronic instruments, the electric guitar remains primarily associated with rock and jazz music, rather than with classical compositions and performances.
Simple Sound Physics Related Specifically to the Guitar
If you put your finger gently on a loudspeaker you will feel it vibrate - if it is playing a low note loudly you can see it moving. When it moves forwards, it compresses the air next to it, which raises its pressure. Some of this air flows outwards, compressing the next layer of air. The disturbance in the air spreads out as a travelling sound wave. Ultimately this sound wave causes a very tiny vibration in your eardrum - but that's another story.
At any point in the air near the source of sound, the molecules are moving backwards and forwards, and the air pressure varies up and down by very small amounts. The number of vibrations per second is called the frequency which is measured in cycles per second or Hertz (Hz). The pitch of a note is almost entirely determined by the frequency: high frequency for high pitch and low for low. For example, 110 vibrations per second (110 Hz) is the frequency of vibration of the A string on a guitar. The A above that (second fret on the G string) is 220 Hz. The next A (5th fret on the high E string) is 440 Hz, which is the orchestral tuning A. (The guitar A string plays the A normally written at the bottom of the bass clef. In guitar music, however, it is normally written an octave higher.) We can hear sounds from about 15 Hz to 20 kHz (1 kHz = 1000 Hz). The lowest note on the standard guitar is E at about 83 Hz, but a bass guitar can play down to 41 Hz. The orginary guitar can play notes with fundamental frequencies above 1 kHz. Human ears are most sensitive to sounds between 1 and 4 kHz - about two to four octaves above middle C. Although the fundamental frequency of the guitar notes do not usually go up into this range, the instrument does output acoustic power in this range, in the higher harmonics of the most of its notes. (For an introduction to harmonics, see Strings and standing waves. To relate notes to frequencies, see Notes and frequencies. )
The pitch of a vibrating string depends on four things. The mass of the string: more massive strings vibrate more slowly. On steel string guitars, the strings get thicker from high to low. On classical guitars, the size change is complicated by a change in density: the low density nylon strings get thicker from the E to B to G; then the higher density wire-wound nylon strings get thicker from D to A to E.
The frequency can also be changed by changing the tension in the string using the tuning pegs: tighter gives higher pitch. This is what what you do when you tune up.
The frequency also depends on the length of the string that is free to vibrate. In playing, you change this by holding the string firmly against the fingerboard with a finger of the left hand. Shortening the string (stopping it on a higher fret) gives higher pitch.
Finally there is the mode of vibration, which is a whole interesting topic on its own. For more about strings and harmonics, see Strings and standing waves.
The strings themselves make hardly any noise: they are thin and slip easily through the air without making much of disturbance - and a sound wave is a disturbance of the air. An electric guitar played without an amplifier makes little noise, and an acoustic guitar would be much quieter without the vibrations of its bridge and body. In an acoustic guitar, the vibration of the string is transferred via the bridge and saddle to the top plate body of the guitar.
The body serves to transmit the vibration of the bridge into vibration of the air around it. For this it needs a relatively large surface area so that it can push a reasonable amount of air backwards and forwards. The top plate is made so that it can vibrate up and down relatively easily. It is usually made of spruce or another light, springy wood, about 2.5 mm thick. On the inside of the plate is a series of braces. These strengthen the plate. An important function is to keep the plate flat, despite the action of the strings which tends to make the saddle rotate. The braces also affect the way in which the top plate vibrates. For more information about vibrations in the top plate and in the body, see the links below. The back plate is much less important acoustically for most frequencies, partly because it is held against the player's body. The sides of the guitar do not vibrate much in the direction perpendicular to their surface, and so do not radiate much sound. It is worth making it clear that the body doesn't amplify the sound in the technical sense of amplify. An electronic amplifier takes a signal with small power and, using electrical power from the mains, turns it into a more powerful signal. In an acoustic guitar, all of the sound energy that is produced by the body originally comes from energy put into the string by the guitarists finger. The purpose of the body is to make that conversion process more efficient. In an electric guitar, very little of the energy of the plucked string is converted to sound.
The Air Inside
The air inside the body is quite important, especially for the low range on the instrument. It can vibrate a little like the air in a bottle when you blow across the top. In fact if you sing a note somewhere between F#2 and A2 (it depends on the guitar) while holding your ear close to the sound hole, you will hear the air in the body resonating. This is called the Helmholtz resonance and is introduced below. Another way to hear the effect of this resonance is to play the open A string and, while it is sounding, move a piece of cardboard or paper back and forth across the soundhole. This stops the resonance (or shifts it to a lower frequency) and you will notice the loss of bass response when you close up the hole. The air inside is also coupled effectively to the lowest resonance of the top plate. Together they give a strong resonance at about an octave above the main air resonance. The air also couples the motion of the top and back plates to some extent. The Helmholtz resonance of a guitar is due to the air at the soundhole oscillating, driven by the springiness of the air inside the body. I expect that everyone has blown across the top of a bottle and enjoyed the surprisingly low pitched note that results. This lowest guitar resonance is similar. Air is springy: when you compress it, its pressure increases. Consider a 'lump' of air at the soundhole. If this moves into the body a small distance, it compresses the internal air. That pressure now drives the 'lump' of air out but, when it gets to its original position, its momentum takes it on outside the body a small distance. This rarifies the air inside the body, which then sucks the 'lump' of air back in. It can thus vibrate like a mass on a spring. In practice, it is not just the compression of the air in the body, but also the distension of the body itself which generates the higher pressure. This is analysed quantitatively in Helmholtz Resonance.
Acoustically Important Construction Features
Three main features:
- Material Composition
- Plate Bracing
'Coupling' simply refers to an interaction between two or more vibrating elements. First of all, on a guitar, the string is excited (plucked or picked) by your fingers, vibrating the bridge, which then goes on to vibrate the soundboard and the internal air cavity, then the back and sides and so on. If these these elements interact well, the whole system is said to be strongly coupled.
The body of the guitar acts so that the high pressure vibrations at the bridge are turned into low pressure vibrations of the surrounding air. This is a form of "impedance matching", in much the same way an electrical transformer raises or lowers a potential difference and is the main principle behind speaker cone design.
The higher frequency (pitch) sounds are produced by string interaction with the bridge and then the sound board, whereas the lower frequencies are essentially driven by the internal air cavity/sound hole and ribs/back coupling effects.
Schematic of Frequency-dependent Component Oscillations. Arrows show main direction of vibratory interaction. Note that some of these influences act in both directions as mechanical feedback, eg. Bridge vibration affects the string's motion as a secondary influence.
Coupling between parts depends on geometry, sound frequency and the materials used.
Interaction strengths between various components need to be optimised according to taste; a certain amount is needed to radiate the sound transferred from the string's vibration, but too much coupling produces some harsh and very ugly tones.
Coupling can be, and is to an extent, controlled during construction; luthiers often make use of Chladni pattern diagnosis to check the main resonance symmetries of their instrument and make any necessary changes.
Apart from being sensitively dependent on materials and bracing (see below) various other factors also influence coupling strengths, such as purfling and binding (how the sides and top/back plates are connected), bridge type and placement, right down to what sort of adhesive was used during manufacture.
The soundhole is designed so that the body acts as a Helmholtz resonator, (tuned roughly to A2 (55.0 Hz) for steel-strings, G#2 (103.8 Hz) for classical and between F#2 and G2 (92.5-98.0 Hz) for Flamenco guitars.)
The materials from which a guitar is constructed have very direct consequences on its acoustic qualities. Because the traditional material used is wood--- often rare hardwoods and cut from as close to the centre as possible---there are certain economic and conservation issues that would be partly addressed if a more readily obtained and controllable medium were to have the required acoustic properties. Much work has been done on testing the various acoustic properties of materials that comprise the guitar. Investigations have been carried out using synthesised materials such as fibreglass, carbon fibre and various polymers, in attempts to imitate/replace existing woods. The general rationale was to produce materials with much less variation and at less cost than traditional woods, but so far the results have not been promising:
The attempts studied tended to have as much acoustic variation as traditional woods; and
Still didn't have the stiffness-to-mass ratio, elastic moduli, damping, or longitudinal to lateral grain properties required to compete with traditional timbers.
Despite this, synthetic materials are used successfully in complementing traditional materials (such as carbon-fibre strut reinforcement on some soundboards), but it appears a pure synthetic that has a good sound and yet feels good to play is still some time away. It should also be mentioned that aesthetic considerations also play a large part in purchasing a guitar---even if an instrument sounds good, it won't be very popular if it looks like a politician!
Unlike many other stringed instruments (such as the violin family) the guitar has a braced sound board and back plate. This is primarily due to the central position of the bridge and saddle and the large surface area of the soundboard and back, combined with their relative thinness and having no soundpost.
The guitar requires additional structural support. The modern, conventional, 'fan-bracing' was originally developed by the famous luthier Antonio de Torres Juan (1817-1892). A recent major development in soundboard bracing was made by Australian luthier, Greg Smallman. The structure utilises a 'criss-cross' lattice bracing composed of carbon fibre/epoxy and balsa braces, tapering in height radially outwards from underneath the bridge saddle. Dr Michael Kasha has experimented with various asymmetric bracing geometries.The bracing is acoustically critical: varying bracing techniques will alter the stiffness-to-mass ratios and elastic moduli tremendously, thereby affecting how the guitar radiates sound.
Some examples of guitar bracing geometries
Some of the designs above may seem a little archaic or bizarre, but they were generally devised with a specific purpose. One problem encountered with guitars is that, with a symmetric bracing pattern, at a certain frequency, a node (position where vibration is a minimum) may be produced right on the point where the string that created the note is positioned, meaning that you can play the particular note on that string really quite hard, yet the sound created will have a fairly low intensity---this can often occur in the 'tripole' mode of the guitar. To counteract this effect, bracing patterns may be offset, so that the resonance modes are slightly asymmetric.
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