當提到聲學吉他時，最多人會想到琴身上有一個音孔的「平型」（flat top）吉他。然而，吉他還有許多不同的外型和風格，每一種都有不同的音色。聲學吉他有最主要的兩個種類，分別是琴頸較小、使用鋼鐵弦的「鐵弦吉他」（steel stringed），以及琴頸較寬、使用尼龍弦的「古典吉他」（classicals）。鐵弦吉他的音色較為溫和（雖然有時也會有金屬的感覺），適合演奏廣泛的流行音樂類型，包括鄉村、流行和搖滾。古典吉他則大多用於演奏鄉村藍調、繁拍（ragtime）和民謠。兩種吉他都能使用撥子（plectrum）或匹克（pick）以各種風格演奏。
任何聲學吉他的主體是大並中空的；它作為共鳴箱來放大吉他弦的聲音。 A simple proof would be to strike an open string and as the note is sounding lightly place a finger on the table of the guitar. You should feel the wood gently vibrating to the struck note. Larger bodied guitars with bigger curves tend to have a deeper or heavier tone, while guitars with a smaller body tend to sound brighter. Acoustic guitars sometimes have cutaways, similar to the cutaway on the Gibson Les Paul shown in the picture below, which allows greater access to the higher frets. This also changes the tone. Acoustic guitars have a weaker sustain than electric guitars but master-built classical or steel-string guitars often feature very good sustain and excellent overall performance. There are many entry-level acoustic guitar models that are manufactured to a high standard that are entirely suitable as a first guitar for beginners. If you wish to buy something more expensive then it is important that the front should be made from a single piece of wood (not ply) and closely grained.
The timbre (pronounced tam - ber) of the acoustic guitar lends itself to a variety of tasks and roles. It's a songwriter's tool because of its portability and ease of use and its gentle harp-like arpeggios and rhythmic chordal strumming has always found favour in an ensemble setting. When the performance is in a personal setting or amphitheater, the acoustic guitar can be heard with no additional amplification because the resonating chamber of the guitar itself creates acoustic amplification. In some situations the acoustic guitar is not loud enough to be heard by all the people in an audience and amplification is required. An acoustic guitar can be amplified by placing a microphone several inches from the sound hole or by installing a pickup designed for acoustic guitars. The need for guitars that retain their acoustic qualities when plugged into an amp or PA has led to the invention of the electro-acoustic guitar.
w:zh:電吉他（electric guitar）是搖滾音樂的必備樂器，但也用在其它類型的音樂中，如藍調，爵士和流行。 電吉他需要與放大器連接使其聲音能讓人聽到。它們通常是實心吉他，但也有F孔的空心電吉他，這種結構賦予這種吉他一些聲學共鳴（見下）。The timbre of the electric guitar is not comparable to the timbre of an acoustic guitar. The pickups are vital to the sound of the guitar. The pickups and amplifier used with a solid-body electric guitar creates a sound that is metallic with a lengthy decay (sustain).
The design of the electric guitar is not determined by the need for the deep resonating body that acoustic guitars must possess and this had led to the development of contoured and thin electric guitars which can be more comfortable to hold and play. The design variations amongst electric guitars allows them to produce a wide variety of tones. The two most popular basic shapes of the electric guitar are the Fender Stratocaster design and the Gibson Les Paul design. The strings of an electric guitar are thinner than the strings of an acoustic and closer to the neck; therefore less force is needed to press them down. The electric guitar is capable of producing sounds and effects that would be difficult on an acoustic. The ease of bending strings sometimes used in combination with a whammy bar has created some of the greatest modern guitar solos. Fret-tapping is an electric guitar technique that has led to a different way of using the fretboard; allowing chords and melody lines to be played that would have been impossible using the standard technique of strumming and fingerpicking.
The choice of amplifier is fundamental to the sound created and should be regarded as the second half of the guitar. See the Buying an Amplifier section for details. Seven-string electric guitars have a string above the low E string which is tuned to a B and lower in pitch than the low E. They are popular with guitarists who play metal music.
Electro-acoustic guitars have pickups specifically designed for the subtle nuances of the timbre of the acoustic guitar. This allows electro-acoustics to be plugged into a PA and they are essential for many guitarists who rely on using the house PA when they gig. The Ovation range of electro-acoustics is a prime example of the departure in design from ordinary acoustics. Ovation guitars use under-the-saddle piezo pickups and a synthetic bowl-back. Purists were derisory of Ovation's innovations but professional musicians found that the synthetic bowl-back provided a tough construction that stands up to the rigours of the road and offered less feedback at high volumes. Ovation were the first company to provide on-board equalization and this is now a standard feature found on most electro-acoustics. Electro-acoustic pickups are designed to sound neutral with little alteration to the organic acoustic timbre. Another famous electro-acoustic brand is the Taylor guitar range. Taylor uses the traditional all-wood construction and the necks of these guitars have a reputation for superb action and playability.
The twelve-string is usually an acoustic though twelve-string electric guitars are available. Twelve-string guitars are not the same as double-neck guitars. Double-neck guitars are essentially two guitar necks bolted onto one body. Twelve-string guitars have the regular six strings and a second set of thinner strings with each string of the second set corresponding to the note of its regular string counterpart. The second set of strings are tuned an octave higher. The strings form pairs; so you still play the guitar in the same manner as a standard six-string.
Twelve-string guitars produce a brighter and more prominent tone and are harder to play than a standard six-string guitar. They are usually confined to niche roles, such as rhythm guitar. The additional strings require more pressure to press down and bending notes also requires an extra muscular effort. Twelve-string guitars are more expensive to buy than the standard acoustic or electric and may need more maintenance because of the strain the additional strings place on the neck.
An archtop is a hollow or semi-hollow acoustic or electric guitar which uses steel strings. The arched top creates a unique timbre and other elements taken from the design of the mandolin or violin also add to the distinctive tone of the archtop guitar. The body of the archtop guitar, whether hollow or semi-hollow, has a sound block in the middle and they also have violin f-holes cut into the table.
Archtop guitars may be acoustic or electric and can look very similar with the only distinguishing feature being an electromagnetic pickup. One problem with archtop hollow-bodied guitars is that when played through an amplifier they tend to generate feedback. The semi-hollow archtop was developed to make feedback less of an issue. Archtop guitars have been particularly popular in jazz music because their thicker strings add tone.
Some solid-body electric guitars have an arched top body shape but the name archtop is usually reserved for the hollow and semi-hollow guitar.
The steel guitar is unusual in that it is played horizontally, either across the players knees or on its own stand. There are two main varieties of the instrument, which are played using the metal slide, or 'steel' from which the guitar takes its name. The steel is held in the left hand, when used by a right-handed player. The two main variations are the lap steel guitar, which typically has six strings and the pedal steel guitar which can have more - sometimes two or even three separate sets; each tuned differently. Pedals and knee-levers are used to alter the tuning on particular strings whilst playing, which along with the sliding action of the steel, gives the pedal steel its distinctive voice which is most often heard in country music.
Often also called 'steel' guitars due to some models possessing metal bodies. The acoustic resonator guitar is distinctive in not having a regular sound hole. Resonator guitars have a large, usually circular—plate which conceals the resonator cone. The cone closely resembles an audio loudspeaker and is made from spun aluminium. The bridge of the guitar is connected either to the centre of the cone or to the edge by an aluminium 'spider' and the strings' vibrations are thus amplified and projected outwards through the perforated plate on the guitar's top. The most common resonator guitars have a single cone, although the original model has three. Resonators possess a loud, bright voice, making them easily heard in a large room or open air performance. They are popular with blues musicians and country players and can be played in the conventional style or with a metal or glass slide.
The bass guitar has a longer scale-length and thicker strings than a standard guitar. These factors create a range of notes that are pitched an octave lower than the guitar. Often the bass is considered part of the rhythm section but there are some players whose skills are comparable to any other soloist. Acoustic and electric bass guitars are available but the electric bass is more common. The standard bass is the four string bass though five and six string basses are also manufactured. The four strings of the bass correspond to the lowest four strings of the guitar an octave lower.
The double-neck guitar is basically two different kinds of guitar sharing one body. This design allows the guitarist to easily access and switch between either neck. Made famous by Jimmy Page, the double neck guitar typically will have a standard six-string neck and a twelve-string neck. Other combinations exist, such as a six-string and bass or a six-string with frets and its fretless version. Steve Vai has been known to play a triple-neck guitar. The double-neck guitar came about in the 1970s because of the changes in recording technology. The recording technology of the 1960s relied on only 4 tracks and multi-layered guitar parts, though possible, were not frequently used. The bands of the 1960s would usually have two guitarists and this achieved the desired affect. The invention of 8 track recording meant more freedom to create complex guitar parts. The guitarist could lay down the rhythm track using a twelve-string guitar and then record onto a separate track, the lead break using a six-string guitar. This left the problem of how a single guitarist could perform these parts live without stopping to change guitars and the double-neck guitar provided the solution.