Amplification
A steel-string guitar can be amplified with a:
- microphone, possibly clipped to the guitar body;
- detachable pickup, often straddling the soundhole and using the same magnetic principle as a traditional electric guitar; or
- transducer built into the body.
The last type of guitar is commonly called an "acoustic-electric" or "electro-acoustic" guitar, as it can be played either "unplugged" as an acoustic or plugged in as an electric. The most common type is a piezoelectric pickup, which is composed of a thin sandwich of quartz crystal. When compressed, the crystal produces a small electrical current, so when placed under the bridge saddle, the vibrations of the strings through the saddle, and of the body of the instrument, are converted to a weak electrical signal. This signal is often sent to a pre-amplifier, which increases the signal strength and normally incorporates an equalizer. The output of the preamplifier then goes to a separate amplifier system similar to that for an electric guitar.
Several manufacturers produce specialised acoustic guitar amplifiers, which are designed to give undistorted and full-range reproduction.
Read more about this topic: Steel-string Acoustic Guitar