An acoustic guitar is a guitar that produces sound acoustically by transmitting the vibration of the strings to the air—as opposed to relying on electronic amplification (see electric guitar). The sound waves from the strings of an acoustic guitar resonate through the guitar's body, creating sound.
The acoustic-electric guitar, also known as electro-acoustic, is identical in construction, acoustic properties, and guitar components to an acoustic guitar. The difference lies in the addition of the “electronics” fitted onto an acoustic electric guitar.
The slide technique of playing slide guitar is generally by using a steel bar. Resonator guitars, including round necked varieties, are particularly suitable for this style, yet are seldom referred to as "steel guitars", but rather referred to generally as a Dobro, acoustic slide guitar, or square neck resonator guitars.
Twelve-string guitar. The twelve-string guitar is a steel-string guitar with twelve strings in six courses, which produces a richer, more ringing tone than a standard six-string guitar. Typically, the strings of the lower four courses are tuned in octaves, with those of the upper two courses tuned in unisons.