However, because the string can only displace 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.
Some of the most important varieties are the classical guitar (nylon-stringed), steel-string acoustic guitar and lap steel guitar. A more complete list is given below, refer to the individual articles for more specific detail.
Source: Wikipedia > Acoustic Guitar
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