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semi-acoustic guitar

also: hollow-body electric guitar, archtop electric guitar

semi-acoustic guitar
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semi-acoustic guitar
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Overview

Contextual Associations

The semi-acoustic guitar is a plucked box-lute chordophone initially developed and manufactured in the United States but that has subsequently come to be distributed and manufactured internationally. While morphologically similar in many ways to the acoustic electric guitar, it also differs from it in at least two significant ways: the design of its resonator (archtop soundboard with f-holes instead of flat soundboard with a circular soundhole); and the type of pickups used (magnetic pickups under the strings instead of piezoelectric ones imbedded in the soundboard and bridge). A product of the mid-1930s, a time when guitar makers were experimenting with all sorts of design ideas to increase the volume of the guitar for use in increasingly loud ensemble combinations, the semi-acoustic guitar, like its other guitar relatives, is ideal both for song accompaniment and for use as a solo instrument. It is therefore used by artists in a wide range of vernacular American musics, including blues, jazz, rhythm and blues, country, and rock.

Description

Maple is used for the sides and back of the hollow resonator of the semi-acoustic guitar pictured here, and spruce for its soundboard. The shape of the relatively shallow resonator might be described as dreadnought with a cutout shoulder. The soundboard and back of the resonator arch outwards, which is why guitars with this feature are called ‘archtops’. F-holes are cut into the resonator soundboard rather than a central circular soundhole found on other varieties of guitars. An adjustable pressure bridge is located at the center of the soundboard. A pick guard made of synthetic material is glued to one side of the soundhole to reduce damage to the soundboard should the performer use a pick to strum the strings. (The various knobs, switches and pickups located on the soundboard will be discussed at the end of this paragraph.) To compensate for the greater tension that steel strings exert on the string carrier, the joining of the base of the neck to the resonator must be particularly strong and generally involves bolts. The neck and peg head are carved from a single piece of maple and a thin and flat fingerboard or rosewood is glued to the top face of the neck. The fingerboard extends beyond the neck over the resonator soundboard up to the sound hole. Twenty metal frets are set in horizontal grooves cut into the fingerboard; the neck meets the resonator at the fourteenth fret, the final six frets are located over the resonator. The bottom ends of the six steel wire strings are attached to a metal tailpiece, which in turn is anchored to the resonator side at the bottom end of the instrument. After running in a parallel plane over the bridge and continuing just slightly above the pickups and the fretted fingerboard (see first detail image), the strings pass over a nut (a raised ridge that separates the fingerboard from the tuning block) before being wound around the capstans of the back-mounted metal machine heads with their laterally-situated knobs (see the second and third detail images). The acoustically active length of all the strings (the distance between the bridge and the nut) is 25 inches. Thus far the description has focused on this guitar as an acoustic instrument, but now we will turn our attention to its electronic features. On the soundboard, underneath the plane of the strings and between the bridge and the lower end of the fingerboard, are located two rectangular pickups (see the fourth detail image). Pickups are magnetic transducers that convert the energy being put out by the vibrating strings into an electrical signal. The pickup closest to the bridge is called the treble pickup, the other the bass pickup. A Rhythm/Treble toggle switch (see the fifth detail image) mixes the signals from the two pickups so that their bass frequencies are favored (the ‘Rhythm’ setting, for playing the instrument as a rhythm guitar) or their treble frequencies (the ‘Treble’ setting, for solo playing) are favored. The remaining four knobs (see the sixth detail image) are for tone and volume control (one tone and one volume control for each pickup). The electrical signal, however shaped by the performer through the settings selected with the knobs, is then sent through a cable to an external amplifier and speaker (seen in the gallery image).

Player - Instrument Interface and Sound Production

The playing position and sounding techniques (plucked or strummed, fully stopped and harmonic notes) of the semi-acoustic guitar are shared with the classical guitar. The guitar is fully chromatic over a range of three-and-one-half octaves, from E2 - C6, and uses the standard guitar tuning of E2 - A2 - D3 - G3 - B3 - E4 (interval pattern of P4 - P4 - P4 - M3 - P4). The dynamic potential of this guitar is greatly increased by its electronic component, which also allows the guitarist increased control over shaping the tone of the instrument as heard through a loudspeaker.

Origins/History/Evolution

A demand for louder guitars for use in dance bands and other genres of popular music in the first few decades of the 20th century stimulated makers to modify existing guitar designs. The first hollow-body, archtop, semi-acoustic electric guitars like the one discussed here were produced in the United States by Gibson in 1936. While the design of the pickups and other element in the electronics of such guitars have improved over the years, the semi-acoustic guitar pictured here is for all practical purposes the same as the early Gibson guitar.

Bibliographic Citations

Bacon, Tony. 1984. "Electric guitar," NGDMI v.1: 651-654.

Campbell, Murray, Clive Greated, and Arnold Meyers. 2004. Musical Instruments: History, Technology, and Performance of Instruments of Western Music. Oxford: Oxford University Press.

Gruhn, George, and Walter Carter. 1994. Electric Guitars and Basses: A Photographic History. San Francisco: GPI Books.