In order for an acoustic guitar to be connected to an amplified source it must have some kind of interface, either in the shape of a microphone, transducer or pick-up, which is capable of converting the sound from the acoustic guitar into an electronic signal for the purpose of amplification. Once the acoustic instrument has the required pick-up or sound sensor it can be plugged into an amplifier or PA system.
Natural Sounding Acoustic Amplifiers
Some manufacturers have now started to produce acoustic/electro-acoustic guitar amplifiers which have been specifically designed for an acoustic instrument. Typically this category of amplifier has a flat sound so that it naturally re-creates the sound of the acoustic instrument without "colouring" the frequencies.
In most cases acoustic guitar amplifiers are combo amps with the speaker and amplifiers within the same chassis, they sometimes have a few on-board effects such as reverb, chorus and in some cases a compressor limiter which fattens the sound and ensures that every note has the same uniform volume level.