Body (acoustic guitar)

In acoustic guitars, string vibration is transmitted through the bridge and saddle to the body via sound board. The sound board is typically made of tone woods such as spruce or cedar. Timbers for tone woods are chosen for both strength and ability to transfer mechanical energy from the strings to the air within the guitar body. Sound is further shaped by the characteristics of the guitar body's resonant cavity.
In electric guitars, transducers known as pickups convert string vibration to an electric signal, which in turn is amplified and fed to speakers, which vibrate the air to produce the sounds we hear. Nevertheless, the body of the electric guitar still performs a role in shaping the resultant tonal signature.
In an acoustic instrument, the body of the guitar is a major determinant of the overall sound quality. The guitar top, or soundboard, is a finely crafted and engineered element made of tonewoods such as spruce and red cedar. This thin piece of wood, often only 2 or 3 mm thick, is strengthened by differing types of internal bracing. Many luthiers consider the top the dominant factor in determining the sound quality. The majority of the instrument's sound is heard through the vibration of the guitar top as the energy of the vibrating strings is transferred to it.
Body size, shape and style has changed over time. 19th century guitars, now known as salon guitars, were smaller than modern instruments. Differing patterns of internal bracing have been used over time by luthiers. Torres, Hauser, Ramirez, Fleta, and C.F. Martin were among the most influential designers of their time. Bracing not only strengthens the top against potential collapse due to the stress exerted by the tensioned strings, but also affects the resonance characteristics of the top. The back and sides are made out of a variety of timbers such as mahogany, Indian rosewood and highly regarded Brazilian rosewood (Dalbergia nigra). Each one is primarily chosen for their aesthetic effect and can be decorated with inlays and purfling.
The body of an acoustic guitar has a sound hole through which sound projects. The sound hole is usually a round hole in the top of the guitar under the strings. Air inside the body vibrates as the guitar top and body is vibrated by the strings, and the response of the air cavity at different frequencies is characterized, like the rest of the guitar body, by a number of resonance modes at which it responds more strongly.
Instruments with larger areas for the guitar top were introduced by Martin in an attempt to create louder volume levels. The popularity of the larger "dreadnought" body size amongst acoustic performers is related to the greater sound volume produced.

Body (electric guitar)

Most electric guitar bodies are made of wood, and include a plastic pick guard. Boards wide enough to use as a solid body are very expensive due to the worldwide depletion of hardwood stock since the 1970s, so the wood is rarely one solid piece. Most bodies are made of two pieces of wood with some of them including a seam running down the center line of the body. The most common woods used for electric guitar body construction include maple, basswood, ash, poplar, alder, and mahogany. Many bodies consist of good sounding but inexpensive woods, like ash, with a "top," or thin layer of another, more attractive wood (such as maple with a natural "flame" pattern) glued to the top of the basic wood. Guitars constructed like this are often called "flame tops." The body is usually carved or routed to accept the other elements, such as the bridge, pickup, neck, and other electronic components. Most electrics have a polyurethane or nitrocellulose lacquer finish. Other alternative materials to wood, are used in guitar body construction. Some of these include carbon composites, plastic material (such as polycarbonate), and aluminum alloys.