Acoustic Guitars
An acoustic guitar is a guitar that uses only acoustic methods to project the sound produced by its strings. It is a retronym, coined after the advent of electric guitars, which depend on electronic amplification to make their sound audible.
In all types of guitars, the sound is produced by the vibration of the strings. However, because the strings can displace only a small amount of air, the volume of the sound needs to be increased in order to be heard. In an acoustic guitar, this is accomplished by using a soundboard and a resonant cavity, the sound box. The body of the guitar is hollow. The vibrating strings drive the soundboard through the bridge, making it vibrate. The soundboard has a larger surface area and thus displaces a larger volume of air, producing a much louder sound than the strings alone.
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.
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The materials and shape of the guitar produce a complex series of damping, resonating, and phase cancelling or reinforcing effects. The range of factors determine the overall acoustic qualities or timbre of the instrument. Artisan luthiers tap potential pieces of wood to determine their acoustic resonance, but this is usually not done for mass-produced instruments. Different timber species have different tones and careful selection of timber is required when designing and making an instrument. Guitars have been made with steel soundboards and resonators, and some experiments have been conducted with novel materials including aluminium and plastics. Even the hardness or viscoelasticity of the glues and varnishes can have a dramatic effect on the sound, damping or resonating some or all frequencies. Quality instruments are made with hard glues and lacquers which have less damping on the transmission of vibrations around the structure of the instrument. Most people prefer the sound of wooden instruments, although the steel resonator guitar has found favor in some genres, like blues. Sitka spruce is traditionally the favored material for the soundboard because of its high strength-to-weight ratio and stiffness. In recent years King William pine has been found to produce very good results.
