An electric acoustic guitar is by esign an acoustic guitar fitted with pickups, a microphone, or transducers. In Electric-Acoustic Classical Guitars, the transducers and microphones are always used because conventional pickups are not capable of picking up vibrations of materials other than metal. The term is not synonymous with that of a semi-acoustic guitar, which is conceptually an electric guitars but with the addition of sound chambers within the guitar body. Usually, electric acoustic guitars are fitted with piezoelectric pickups, and hence require a preamplifier incorporated into the guitar body to amplify the signal before it travels to the main guitar amplifier. These preamps may also come with tone controls of varying types, but usually equalizers with up to six frequency bands are used. They are also referred to it as a plug-in acoustic guitar, due to their ability to simply 'plug in' to a speaker system without the need for microphones.