The term backline is used in popular music and sound reinforcement system contexts to refer to electronic audio amplification equipment and speaker enclosures that are placed behind the band or the rhythm section on stage, including amplifiers and speaker cabinets for guitars, bass guitars and keyboards. In the US and Canada, the term has expanded to include many of the musical instruments that the rhythm section musicians play, including pianos, Hammond organs, drum kits and various percussion instruments such as congas and bongos.
The type of backline equipment varies according to the style of music played in a venue or performance space. A heavy metal music club will typically have a large, powerful Marshall guitar stack. In contrast, a blues or country music bar will typically have a Fender Bassman or other traditional "tweed" guitar amplifier. A jazz club usually has a grand piano for jazz pianists. For bass players, a small jazz club may have a mid-sized, moderately powered "combo" amp, which includes the power amplifier and one or more speakers in a wooden cabinet; a rock nightclub may have a large, powerful "bass stack", which pairs a power amplifier with one or two big speaker cabinets.
The term is used in contracts signed by bands with music festivals and venues. Top bands may have very specific backline requirements, which not only include a list of amplifiers and instruments that are required, but also include the brand names and model numbers. The term is often used in this sense to talk generally about the equipment available to or needed by musicians. (e.g. "What is the backline at the music festival? The band wants to know if they need to bring their own drums or amps.")
In rock music's early days in the early 1960s, PA systems were not very loud or powerful. As a result, 1960s rock bands typically used the PA system just for the vocals, even if they were playing at a large venue. As a result, the rhythm section musicians playing electric guitar, electric bass and keyboards were expected to produce enough volume to fill the venue using their own instrument amplifiers. To achieve venue-filling sound with their instruments, bands from the 1960s typically used large, powerful guitar "stacks" and big speaker enclosures. A standard cabinet used by guitarists and bassists during this era was the heavy 8x10" cabinet, which contained eight ten inch speakers. Some performers even "daisy-chained" several amplifiers together to create a louder sound, particularly with groups from the heavy metal music genre.
During the 1960s, the PA speakers for the vocals and the band's amplification were all set in a line, which conceptually grouped PA and instrument amplification together. This changed over the 1970s and 1980s, as PA systems became powerful enough to amplify all of the band's instruments and the vocals. During this era, the backline gear was set behind the PA speakers to create the modern audio stage set-up. Modern monitoring techniques, in which monitor speakers pointing at the performers are placed on the stage, as well as the concepts of frontline and backline, developed during this era.
Backline equipment can be rented for concert tours or recording studio use. Many travelling musicians prefer not to transport their own backline gear across borders and continents for fear of damage or customs hassles, which makes renting backline equipment while on tour an attractive option. Many music festivals and performance venues provide backline equipment. In some countries, all electronic and electric gear needs documentation and certification by an electrical expert before it can be brought into the country. Another issue is that some bands may travel to a country or continent which uses a different type of AC mains power and differently-shaped electric plugs.
Festivals and venues provide backline gear because it speeds up the process of changing bands on a stage, in cases where multiple bands are performing in the same day or evening, because the drums, bass amps, keyboards, and so on, do not have to be moved on and off the stage and then soundchecked again. A TV variety show which is featuring performances by several bands will use a backline to speed up the transitions between bands. If the guitarists, bassists, keyboardists and drummers all use the same equipment, then there is less setup and soundchecking to do for each new band.
Major recording studios typically have a grand piano for performers to use. They may also have a Hammond organ and a selection of popular guitar amplifiers and guitar speaker cabinets. This makes the recording process more convenient for the performers, as they do not have to move these heavy instruments and music gear into the studio. As with music venues, when a studio owns backline equipment, they can have it set up and ready to record. For example, a studio's grand piano will typically have several microphones set up on stands to capture the piano sound.
Even when there is a backline, musicians are typically expected to bring their own instruments and equipment, with the exception of keyboardists who play Hammond organ or grand piano, who may be able to just come to the venue without any instruments or equipment. Guitarists typically bring their own electric guitars, acoustic guitars, effects units (e.g., reverb and distortion pedals) and picks; bassists typically bring their own electric basses, upright bass and any effects units (e.g., an audio compressor or bass preamplifier) which they regularly use; drummers will still have to bring their own snare drum, drum sticks and, in some cases, cymbals and bass drum pedals. Even though the musicians still have to bring their own instruments and gear, having a backline still speeds up the setup and soundchecking process. For example, with the bassist, the bass stack will already be set up on stage, plugged into the AC mains power, connected with an XLR cable via the amp's DI box output to the mixing console, and a microphone will be set up in front of the speaker on a mic stand (to capture the bass cabinet's tone). With the drummer, even if they have to bring their snare and cymbals, all of the big drums and stands are already set up and mics are set up on stands around the drum kit. All they have to do is put their snare and cymbals on the stands.
Backline guitar technicians and stage crew set up, maintain, repair and put away the backline equipment. Backline gear that is used heavily will need regular maintenance to ensure that it provides reliable performance and high-quality sound. For example, pianos need to be tuned and maintained, tube amplifiers need servicing or new tubes, speaker cabinets may need to have new loudspeakers installed, and drums will need new drumheads. In places where the backline is left in place indefinitely (e.g., in a nightclub's mainstage or a TV variety show studio), the gear may simply be powered down when it is not being used, and a cloth may be placed over top of the equipment so it does not get dusty. In music festivals with outdoor temporary stages, the backline equipment may have to be transported to a locked, climate-controlled storage area at the end of each day, to protect it from theft, vandalism, or inclement weather. Backline techs who travel with touring acts may also be called roadies, although the road crew's role typically is limited to transporting and positioning the instruments and gear. Maintenance and repair of instruments and gear is a specialized task handled by guitar, keyboard and drum technicians.