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A Sympitar is a modern form of guitar combining functional aspects of the guitar and the Indian sitar. This instrument has a unique feature: there is a graphite channel which guides a series of "sympathetic" resonating strings through the neck from the bridge up to the headstock. These strings vibrate or resonate against a "jiwari" bridge, which produces the sustaining drone typically associated with Indian music. The instrument(s) also have at least 6 standard guitar strings which traverse the length of the neck just as they do for a standard steel-string acoustic guitar. Depending on the notes played and on how the sympathetic strings are tuned, the sympitar's sympathetic strings will produce long waves of resonating notes, either in harmonic or enharmonic response.  
The inventor of the sympitar is the master luthier Fred Carlson. 
There are only a few sympitars in existence, all commissioned as custom builds. Notably, Alex de Grassi often plays a custom Carlson sympitar maple with spruce top.  Fred Carlson also spends his time in the workshop building a variation on the sympitar called the "harp sympitar", the first of which, completed in January 2002, was the Oracle Harp Sympitar commissioned by guitarist Jeffrey Titus and dedicated to the memory of Michael Hedges.
An electric guitar is a guitar that requires external amplification in order to be heard at typical performance volumes, unlike a standard acoustic guitar It uses one or more pickups to convert the vibration of its strings into electrical signals, which ultimately are reproduced as sound by loudspeakers. The sound is sometimes shaped or electronically altered to achieve different timbres or tonal qualities on the amplifier settings or the knobs on the guitar from that of an acoustic guitar. Often, this is done through the use of effects such as reverb, distortion and "overdrive"; the latter is considered to be a key element of electric blues guitar music and rock guitar playing.
The guitar is a fretted musical instrument that typically has six strings. It is usually held flat against the player's body and played by strumming or plucking the strings with the dominant hand, while simultaneously pressing selected strings against frets with the fingers of the opposite hand. A plectrum or individual finger picks may also be used to strike the strings. The sound of the guitar is projected either acoustically, by means of a resonant chamber on the instrument, or amplified by an electronic pickup and an amplifier.
String instruments, stringed instruments, or chordophones are musical instruments that produce sound from vibrating strings when a performer plays or sounds the strings in some manner.
The sitar is a plucked stringed instrument, originating from the Indian subcontinent, used in Hindustani classical music. The instrument was invented in medieval India, flourished in the 18th century, and arrived at its present form in 19th-century India. Khusrau Khan, an 18th century figure of Mughal India has been identified by modern scholarship as the originator of Sitar. According to most historians he developed sitar from setar, an Iranian instrument of Abbasid or Safavid origin. Some Indians, however, claim that he developed it from veena but this view is rejected by others for lacking evidence.
The gadulka is a traditional Bulgarian bowed string instrument. Alternate spellings are "gǎdulka", "gudulka" and "g'dulka". Its name comes from a root meaning "to make noise, hum or buzz". The gadulka is an integral part of Bulgarian traditional instrumental ensembles, commonly played in the context of dance music.
Sympathetic strings or resonance strings are auxiliary strings found on many Indian musical instruments, as well as some Western Baroque instruments and a variety of folk instruments. They are typically not played directly by the performer, only indirectly through the tones that are played on the main strings, based on the principle of sympathetic resonance. The resonance is most often heard when the fundamental frequency of the string is in unison or an octave lower or higher than the catalyst note, although it can occur for other intervals, such as a fifth, with less effect.
Surbahar sometimes known as bass sitar, is a plucked string instrument used in the Hindustani classical music of the Indian subcontinent. It is closely related to the sitar, but has a lower pitch. Depending on the instrument's size, it is usually pitched two to five whole steps below the standard sitar.
The Gravikord is a 24 string electric double bridge-harp invented by Robert Grawi in 1984, which is closely related to both the West African kora and the mbira. It was designed to employ a separated double tonal array structure making it possible to easily play cross-rhythms in a polyrhythmic musical style in a modern electro-acoustic instrument. The Gravi-kora is a similar instrument, also developed by Grawi, which is tuned identically to a traditional 21 string kora.
Killick Hinds of Athens, Georgia is active as a composer, performer, and promoter of a wide range of music. He plays quartertone electric guitar, as well as Big Red harp guitar and the H'arpeggione, an 18-stringed upright acoustic instrument with sympathetic strings, both built by Fred Carlson. Equally influenced by improvisational music and "composed" sounds, Killick's style blends primitive folk, heavy metal, and sacred musics from around the world. Killick has played with improvisers including Susan Alcorn, Liz Allbee, Susie Allen, Brent Bagwell, Colin Bragg, Jeff Crouch, Chris Cutler, Jeremiah Cymerman, Brann Dailor, Ernesto Diaz-Infante, Lisle Ellis, Tony Evans, Drew Gardner, the Georgia Guitar Quartet, Vinny Golia, Frank Gratkowski, Mary Halvorson, Blake Helton, Carl Ludwig Huebsch, Henry Kaiser, Ben Kennedy, Harald Kimmig, Habib Koité, Peter Kowald, Craig Lieske, Marshall Marrotte, Jeff McLeod, Tatsuya Nakatani, Larry Ochs, Brian Osborne, Ravi Padmanabha, Dennis Palmer, Dave Rempis, Blaise Siwula, Carl Smith, Bob Stagner, Sándor Szabó, Ken Vandermark, Matthew Welch, and Eric Zinman.
A multi-neck guitar is a guitar that has multiple fingerboard necks. They exist in both electric and acoustic versions. Although multi-neck guitars are quite common today, they are not a modern invention. Examples of multi-neck guitars and lutes go back at least to the Renaissance.
Alex de Grassi is an American fingerstyle guitarist. Tom Wheeler wrote in Guitar Player magazine that his technique is "the kind that shoves fellow pickers to the cliff of decision: should I practice like a madman or chuck it altogether?" De Grassi was invited by his cousin William Ackerman to join the Windham Hill label and became one of the label's best sellers.
A solid-body musical instrument is a string instrument such as a guitar, bass or violin built without its normal sound box and relying on an electromagnetic pickup system to directly detect the vibrations of the strings; these instruments are usually plugged into an instrument amplifier and loudspeaker to be heard. Solid-body instruments are preferred in situations where acoustic feedback may otherwise be a problem and are inherently both less expensive to build and more rugged than acoustic electric instruments.
The bazantar is a custom made string instrument invented by musician Mark Deutsch, who worked on the design between 1993 and 1997.
An acoustic guitar is a musical instrument in the string family. When a string is plucked its vibration is transmitted from the bridge, resonating throughout the top of the guitar. It is also transmitted to the side and back of the instrument, resonating through the air in the body, and producing sound from the sound hole. The original, general term for this stringed instrument is guitar, and the retronym 'acoustic guitar' distinguishes it from an electric guitar, which relies on electronic amplification. Typically, a guitar's body is a sound box, of which the top side serves as a sound board that enhances the vibration sounds of the strings. In standard tuning the guitar's six strings are tuned (low to high) E2 A2 D3 G3 B3 E4.
An experimental musical instrument is a musical instrument that modifies or extends an existing instrument or class of instruments, or defines or creates a new class of instrument. Some are created through simple modifications, such as cracked drum cymbals or metal objects inserted between piano strings in a prepared piano. Some experimental instruments are created from household items like a homemade mute for brass instruments such as bathtub plugs. Other experimental instruments are created from electronic spare parts, or by mixing acoustic instruments with electric components.
Sympathetic resonance or sympathetic vibration is a harmonic phenomenon wherein a passive string or vibratory body responds to external vibrations to which it has a harmonic likeness. The classic example is demonstrated with two similarly-tuned tuning forks. When one fork is struck and held near the other, vibrations are induced in the unstruck fork, even though there is no physical contact between them. In similar fashion, strings will respond to the vibrations of a tuning fork when sufficient harmonic relations exist between them. The effect is most noticeable when the two bodies are tuned in unison or an octave apart, as there is the greatest similarity in vibrational frequency. Sympathetic resonance is an example of injection locking occurring between coupled oscillators, in this case coupled through vibrating air. In musical instruments, sympathetic resonance can produce both desirable and undesirable effects.
There are many varieties of ten-string guitar, including:
The 3rd bridge is an extended playing technique used on the electric guitar and other string instruments that allows a musician to produce distinctive timbres and overtones that are unavailable on a conventional string instrument with two bridges. The timbre created with this technique is close to that of gamelan instruments like the bonang and similar Indonesian types of pitched gongs.
A third bridge can be devised by inserting a rigid preparation object between the strings and the body or neck of the instrument, effectively diving the string into distinct vibrating segments.
The ten string extended-range classical guitar, with fully chromatic, sympathetic string resonance was conceived in 1963 by Narciso Yepes, and constructed by José Ramírez [III]. This instrument is sometimes referred to as the "modern" 10-string guitar to differentiate it from ten-stringed harp guitars of the 19th century.
Experimental luthiers are luthiers who take part in alternative stringed instrument manufacturing or create original string instruments altogether.