Bass guitars are normally made out of wood. Bass guitars have a few main pieces such as a body, neck, fingerboard, frets, and strings. The body is made out of wood. A wooden neck is glued or bolted onto the body. A wooden fingerboard is then glued onto the neck. Then, thin metal strips called frets are glued onto the fingerboard. Frets are placed at specific locations along the fretboard, with each fret representing one half step in the Western tonal scale.
At the bottom of the body is an assembly called the bridge, a large metal assembly into which one end of the strings are fitted. On some designs, the strings are fasted through the back of the body into the bridge; on others, the strings fit into the front side of the bridge. In some basses, there is a cavity inside the back of the body that contains the electrical components of the bass. These are usually called active basses. The bridge often has adjustments that allow the height of the strings to be changed. In addition to the bridge, the other components found on the body include one or more pickups and various knobs or switches that control the sound of the bass.
The pickups are magnetic devices that sit below the strings. As the strings vibrate, an electrical signal is produced which is routed via an instrument cable to an amplifier. Pickups are either "passive", which means they send the signal with no additional amplification, or "active", which process the signal through a pre-amplifier. Some basses feature pickups that can be set to passive or active mode. Basses that have two pickups (generally referred to as bridge and neck pickups) often have a switch that enables the player to select neck-only, bridge-only, or a blended signal. Each pickup may have different tonal qualities that results from its placement relative to the bridge and its components.
At the other end of the fretboard from the body sits the headstock, which generally holds the tuners that permit the player to adjust the tuning of the strings. At the very end the fretboard, where the strings pass from the fretboard to the tuners, we find the nut, a piece made of metal or plastic, with grooves to hold the strings off the fretboard.
Inside most fretboards is a long metal rod, called a trussrod, that is used to adjust the tension on the neck. It is generally desirably to have the neck bowed slightly concave, so that the strings will clear all frets without "buzzing." The amount of bow, along with adjustments made on the bridge, will determine the height of the strings along the fretboard.
The scale of an electric bass - the length of the strings from the nut to the bridge - is generally 34 inches (84 centimeters), although shorter and longer basses are produced. In earlier decades, short-scale basses were more common, since many designers adapted guitar parts for early models. Because in some styles of music, such as heavy metal, the strings are tuned down, longer scaled basses are sometimes favored for such styles, since string tension is higher.
Standard bass guitars have four metal strings, but models with five, six or eight strings are also made. The strings themselves are manufactured in different ways and with different materials to change their tonal qualities.