A semi-acoustic guitar or hollow-body electric is a type of electric guitar that originates from the 1930s. It has both a sound box and one or more electric pickups. This is not the same as an acoustic-electric guitar, which is an acoustic guitar with the addition of pickups or other means of amplification, either added by the manufacturer or the player.
The Bigsby vibrato tailpiece (or Bigsby for short) is a type of mechanical vibrato device for electric guitar designed by Paul A. Bigsby. The device allows musicians to bend the pitch of notes or entire chords with their pick hand for various effects.
The Bigsby was the first successful design of what is now called a "whammy bar", "vibrato bar", or "tremolo arm", although vibrato is the technically correct term for the musical effect it produces. In standard usage, tremolo is a rapid fluctuation of the volume of a note, while vibrato is a fluctuation in pitch. The origin of this nonstandard usage of the term by electric guitarists is attributed to Leo Fender, who also used the term "tremolo" to refer to what is really a vibrato effect (see vibrato unit).
The Bigsby vibrato unit is installed on the top of the guitar and works in conjunction with a rocker bridge. The arm of the Bigsby is spring-loaded and attached to a pivoting metal bar, around which the strings of the guitar are installed. In the neutral or unused position, the pressure of the spring counterbalances the pull of the strings, resulting in constant pitch when the strings are played. When the arm of the Bigsby is pushed down towards the top of the guitar, the bridge rocks forward causing the strings to loosen, lowering their pitch. When the arm is released, the strings return to normal pitch.
The arm may also be lifted slightly to raise the pitch of the strings. The Bigsby is highly controllable within its range of motion and usually requires little force to operate. Lifting the arm too much, however, will result in the spring falling out of the unit making the Bigsby more suitable for downbends, rather than upbends. It is ideally suited to musicians who use slow, subtle, or extended bends. It has limited range compared to tremolo units using longer springs contained internally. Competing units, like the Floyd Rose and the Fender synchronized tremolo (or strat-style) are therefore preferred by some players.