An
acoustic guitar is a
guitarThe guitar is a plucked string instrument, usually played with fingers or a pick. The guitar consists of a body with a rigid neck to which the strings, generally six in number, are attached. Guitars are traditionally constructed of various woods and strung with animal gut or, more recently, with...
that uses only an acoustic sound board. The air in this cavity resonates with the vibrational modes of the string and at low frequencies, which depend on the size of the box, the chamber acts like a
Helmholtz resonatorHelmholtz resonance is the phenomenon of air resonance in a cavity, such as when one blows across the top of an empty bottle. The name comes from a device created in the 1850s by Hermann von Helmholtz, the "Helmholtz resonator", which he, the author of the classic study of acoustic science, used to...
, increasing or decreasing the volume of the sound again depending on whether the air in the box is moving in phase or out of phase with the strings. When in phase, the sound is increased by about 3 decibels and when in opposing phase, it is decreased about 3 decibels. As a Helmholtz resonator, the air at the opening is vibrating in or out of phase with the air in the box and in or out of phase with the strings. These resonance interactions attenuate or amplify the sound at different frequencies, boosting or damping various harmonic tones. Also, the air in the box is coupled to the resonance of the top plate. Together, which cause further interactions. The back of the guitar will also vibrate to a lesser extent, driven by the air in the cavity. Some sound is ultimately projected through the sound hole (some variants of the acoustic guitar omit this hole, or have
holes, like a
violin familyThe violin family of musical instruments was developed in Italy in the sixteenth century. The standard modern violin family consists of the violin, viola, cello, and double bass....
instrument). This sound mixes with the sound produced by the front face of the soundboard. All these complex air coupling interactions, along with the resonant properties of the panels, are a key reason that different guitars will have different tonal qualities. The sound is a complex mixture of harmonics that give the guitar its distinctive sound.
No
amplificationGenerally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
actually occurs in this process, in the sense that no energy is externally added to increase the
loudnessLoudness is the quality of a sound that is primarily a psychological correlate of physical strength . More formally, it is defined as "that attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud."Loudness, a subjective measure, is often...
of the sound (as would be the case with an electronic amplifier). All the energy is provided by the plucking of the string. The function of the entire acoustic system is to maximize intensity of sound, but since total energy remains constant, this comes at the expense of decay time. An unamplified guitar (one with no soundboard at all) would have a low volume, but the strings would vibrate much longer, like a tuning fork. This is because a damped harmonic oscillator decays exponentially, with a mean life inversely proportional to the damping, i.e. the more the volume is increased by the soundboard, the shorter the resulting sound will last.
Amplification
An acoustic guitar can be amplified by using various types of pickups or microphones. The most common type of pickups used for acoustic guitar amplification are piezo and magnetic pickups. Piezo pickups are generally mounted under the bridge saddle of the acoustic guitar and can be plugged into a mixer or amplifier. Magnetic pickups are generally mounted in the sound hole of the acoustic guitar and are very similar to those found in electric guitars. An acoustic guitar with pickups for electrical amplification is known as an acoustic-electric guitar.The acoustic guitar is a bit difficult to amplify faithfully. As of recent, new types of pickups have been introduced to try to amplify the full sound of these instruments.This includes body sensors such as the Taylor Expression system, and systems that include an internal microphone along with the body sensors or under the saddle pickups.
Instruments with larger areas for the guitar top were introduced by Martin in an attempt to create louder volume levels. The popularity of Martin's larger "
dreadnoughtDreadnought is a type of acoustic guitar body developed by guitar manufacturers C.F. Martin & Company. The Dreadnought style has since been copied by other guitar manufacturers and is now a common style of guitar body...
" body size amongst acoustic performers is related to the greater sound volume produced.
Sound can be produced on an acoustic guitar by using the fingers of the playing hand or by using a
plectrumA plectrum is a small flat tool used to pluck or strum a stringed instrument. For hand-held instruments such as guitars and mandolins, the plectrum is often called a pick, and is a separate tool held in the player's hand...
. Some techniques also utilize note created by the fretting hand using techniques such as hammer-ons and pull-offs.
Types
Historical and modern acoustic guitars are extremely varied in their design and construction, far more so than electric guitars. Some of the most important varieties are the
classical guitarThe classical guitar is a 6-stringed plucked string instrument from the family of instruments called chordophones...
(nylon-stringed),
steel-string acoustic guitarA steel-string acoustic guitar is a modern form of guitar descended from the classical guitar, but strung with steel strings for a brighter, louder sound...
and
lap steel guitarThe lap steel guitar is a type of steel guitar, an instrument derived from and similar to the guitar. The player changes pitch by pressing a metal or glass bar against the strings instead of by pressing strings against the fingerboard....
. A more complete list is given below, refer to the individual articles for more specific detail.
- Nylon/gut stringed guitars:
- Renaissance guitar
- Baroque guitar
The Baroque guitar is a guitar from the baroque era , an ancestor of the modern classical guitar. The term is also used for modern instruments made in the same style....
- Romantic guitar
- Classical guitar
The classical guitar is a 6-stringed plucked string instrument from the family of instruments called chordophones...
, the modern version of the original guitar, with nylon strings
- Flamenco guitar
A flamenco guitar is a guitar similar to a classical guitar. Flamenco guitar also refers to toque, the guitar-playing part of the art of Flamenco.-Brief history:...
- Extended-range classical guitar
- Steel stringed guitars:
- Steel-string acoustic guitar
A steel-string acoustic guitar is a modern form of guitar descended from the classical guitar, but strung with steel strings for a brighter, louder sound...
, also known as western, folk or country guitar
- Twelve string guitar
The twelve-string guitar is an acoustic or electric guitar with 12 strings in 6 courses, which produces a richer, more ringing tone than a standard six-string guitar...
- Resonator guitar
A resonator guitar or resophonic guitar is an acoustic guitar whose sound is produced by one or more spun metal cones instead of the wooden sound board . Resonator guitars were originally designed to be louder than conventional acoustic guitars which were overwhelmed by horns and percussion...
(such as the DobroDobro is a registered trademark, now owned by Gibson Guitar Corporation and used for a particular design of resonator guitar.The name has a long and involved history, interwoven with that of the resonator guitar...
)
- Archtop guitar
An archtop guitar is a steel-stringed acoustic or semi-acoustic guitar with a full body and a distinctive arched top, whose sound is particularly popular with blues and jazz players.Typically, an archtop guitar has:* 6 strings...
- Battente guitar
- Lap steel guitar
The lap steel guitar is a type of steel guitar, an instrument derived from and similar to the guitar. The player changes pitch by pressing a metal or glass bar against the strings instead of by pressing strings against the fingerboard....
- Parlor Guitar
Parlor or parlour guitar usually refers to a type of smaller-bodied guitar smaller than that of a concert guitar.The popularity of these guitars peaked between the late 19th century until the 1950s...
- Lyre-guitar
A musical instrument of the chordophone family, the lyre-guitar was a type of guitar shaped like a lyre. Invented in 1780 by Pierre Charles Mareschal, a prominent French luthier, it had six single courses and was tuned like the modern classical guitar, with a fretboard located between two curved...
- Weissenborn
Weissenborn or H. Weissenborn is a brand of lap slide guitar manufactured by Hermann Weissenborn in Los Angeles in the 1920s and 1930s....
-style guitar
- Manouche guitar
- Acoustic bass guitar
The acoustic bass guitar is a bass instrument with a hollow wooden body similar to, though usually somewhat larger than a steel-string acoustic guitar...
- Russian guitar
The Russian guitar is a seven-string acoustic guitar that arrived in Russia toward the end of the 18th century and the beginning of the 19th century, most probably as an evolution of the cittern, kobza, and torban...
- Novelty instruments:
- Pikasso guitar
The Pikasso Guitar, or Pikasso I, is a custom made harp guitar created by Canadian luthier Linda Manzer.Its name is ostensibly derived from its likeness in appearance to the cubist works of Pablo Picasso.-Players:...
- Harp guitar
]The harp guitar is a stringed instrument with a history of well over two centuries. While there are several unrelated historical stringed instruments that have appropriated the name “harp-guitar” over the centuries, the term today is understood as the accepted vernacular to refer to a particular...
- Banjo guitar
- Guitar lute
Lute can refer generally to any plucked string instrument with a neck and a deep round back, or more specifically to an instrument from the family of European lutes....