The acoustic (non-electrified) guitar is the centuries-old ancestor of the electric guitar. The instrument shown here is an example of the modern Spanish-style six-string acoustic guitar that was developed around 1800. Steel strings were introduced in the 19th century to replace traditional gut strings.
Sound is produced by striking the strings and making them vibrate. The energy of the vibrating strings is transferred to the soundboard through the bridge. The guitar's hollow body amplifies the sound of the vibrating strings. The pitch of the vibrating strings depends partly on the mass, tension, and length of the strings.
On steel-string guitars, the lower strings are thicker. Tuning the strings changes the tension; the tighter the string, the higher the pitch. Pressing down on the frets changes the amount of the string that is free to vibrate; the closer the fret is to the sound hole, the shorter the vibrating string, the higher the pitch.
Guitar makers and players have always searched for ways to increase the instrument's volume. Electronic amplification was one of the most successful innovations for building a louder guitar. Some of the earliest electronic experiments from the 1920s and 1930s involved simply attaching a pickup to an acoustic guitar.
An electric-acoustic guitar is also called a hollow-body electric guitar
Electric guitar pioneers tried a variety of ways to pick up the instrument's sound and amplify it. George Beauchamp and Paul Barth developed the first successful electromagnetic pickup system; it was applied to the Rickenbacker Frying Pan guitar, marketed in 1932.
Today, pickups are electromagnets mounted under the guitar strings. They sense the strings' vibrations and convert them into electrical signals that travel through a cable to the amplifier to increase the sound. There are two kinds of pickups: single-coil and double-coil, or humbucking. The latter give a fuller sound.
Solid-Body Electric Guitar
As makers and players continued to investigate ways of increasing the volume of the electric guitar throughout the 1940s, it became clear that a solid body was a key design feature.
In a hollow guitar, the string's vibrations are transferred to the guitar's body. Since the pickup cannot tell string and body vibrations apart, the signal can be jumbled.
In a solid-body guitar, the great mass of the solid body has minimal response to the vibrations of the strings. So the pickup "picks up" a cleaner signal of the strings' pure tone.
When the solid-body guitar is plugged into an amplifier, the electrical impulses created by the pickups are converted into sound by the amplifier. Special-effects boxes, such as the fuzz box that creates a distorted sound, can change the signal from the pickups, which changes the sound that the amplifier produces.
Hawaiian, or Steel, Guitar
Introduced in the United States around 1900, the Hawaiian, or steel, guitar differed from the standard Spanish-style guitar in that it was designed to be played horizontally with a sliding steel bar, a much easier technique than fingering the strings. The lap-steel and pedal-steel are variations of this instrument.
The ease of learning and playing the Hawaiian guitar made it popular with both users and teachers. Its alluring effect of sliding between notes endeared it especially to country and blues musicians.
Hawaiian guitars became the first and most popular style of electric guitars in the 1930s. The electric models were built out of solid wood, a type of construction that was not commercially adapted to Spanish-style guitars until the 1950s.