Foldback is the use of performer-facing loudspeaker cabinets known as monitor speakers or stage monitors on stage during live music performances in which a PA system or sound reinforcement system is used to amplify the performers' singing, music, speech and other sounds for the audience. Monitor speakers often include a single full-range loudspeaker and a horn in a cabinet. Monitor speakers have numerous features which facilitate their transportation and protection, including handles, metal corner protectors, sturdy felt covering or paint and a metal grille to protect the speaker. There are two types of monitors: passive monitors consist of a loudspeaker and horn in a cabinet (they must be plugged into an external power amplifier); active monitors have a loudspeaker, horn and a power amplifier in a single cabinet, which means the signal from the mixing board can be plugged straight into the monitor speaker.
The sound at popular music and rock music concerts is amplified with power amplifiers through a PA system or sound reinforcement system. With the exception of the smallest venues, such as coffeehouses, most mid- to large-sized venues use two sound systems. The main or "front of house" (FOH) system is a PA system/sound reinforcement system which amplifies the onstage sounds for the main audience. The monitor system consists of monitor speakers aimed at the on-stage performers rather than the audience and power amplifiers. The sound signal for the monitor speakers may be produced on the same mixing console as the main mix for the audience (called the "front of house" mix), which is often the case in small venues, such as pubs where singer/guitarists perform. Monitor systems have a huge range of sizes and complexity. A small pub or nightclub may have a single, 100 watt powered monitor speaker onstage so that the lead vocalist can hear her/his singing, with the "aux send" signal from a small powered mixer plugged straight into the monitor cabinet, and the singer setting her/his own levels with the onstage mixer. On the other hand, a stadium rock concert may use a large number of monitor wedges, big racks of power amplifiers with thousands of watts of power, and a separate mixing board and sound engineer for the monitors.
In most mid- to large-size venues, there is a separate sound engineer and mixing console on or beside the stage creating a mix for the monitor system. The monitor mix is often different from the "front of house" mix, because performers may request to hear more of certain accompaniment or rhythm section instruments. In the most sophisticated and expensive monitor set-ups, each onstage performer can ask the sound engineer for a separate monitor mix for separate monitors. For example, the lead singer can ask to hear mostly her/his voice in the monitor in front of her/him and the guitarist can ask to hear mostly the bassist and drummer in her/his monitor.
Without a foldback system, the sound that on-stage performers would hear from front of house would be the reverberated reflections bouncing from the rear wall of the venue. The naturally reflected sound is delayed and distorted, which could, for example, cause the singer to sing out of time with the band. A separate mixed signal is often routed to the foldback speakers, because the performers may also need to hear a mix without electronic effects such as echo and reverb (this is called a "dry mix") to stay in time and in tune with each other. In situations with poor or absent foldback mixes, vocalists may end up singing off-tune or out of time with the band.
For live sound reproduction during popular music concerts in mid- to large-size venues, there are typically two complete loudspeaker systems and PA systems (also called sound reinforcement systems): the "main" or "front of house" system and the "monitor" system. Each system consists of a mixing board, sound processing equipment, power amplifiers, and speakers. The two systems usually share microphones and direct inputs using a splitter microphone snake. There is disagreement over when to call these audio systems Sound Reinforcement (SR) systems or Public Address (PA) systems. This distinction is important in some regions or markets, while in other regions or markets the terms are interchangeable.
The "main" system (also known as "Front of House", commonly abbreviated FOH), which provides the amplified sound for the audience, will typically use a number of powerful amplifiers driving a range of large, heavy-duty loudspeaker cabinets including low-frequency speaker cabinets called subwoofers, full-range speaker cabinets, and high-range horns. A coffeehouse or small bar where singers perform while accompanying themselves on acoustic guitar may have a relatively small, low-powered PA system for the "mains", such as a pair of two 200 watt powered speakers. A large club may use several power amplifiers to provide 1000 to 2000 watts of power to the "main" speakers. An outdoor rock concert may use large racks of a number of power amplifiers to provide 10,000 or more watts.
The "monitor" system reproduces the sounds of the performance and directs them towards the on-stage performers (typically using wedge-shaped monitor speaker cabinets), to help them hear the instruments and vocals. The monitor system in a coffeehouse or singer-songwriter stage for a small bar may be a single 100 watt powered monitor wedge. In the smallest PA systems, the performer may set their own "main" and "monitor" sound levels with a simple powered mixing board. The simplest monitor systems consist of a single monitor speaker for the lead vocalist which amplifies their singing voice, so that they can hear it clearly.
In a large club where rock or metal bands play, the monitor system may use racks of power amplifiers and four to six monitor speakers to provide 500 to 1000 watts of power to the "monitor" speakers. In large venues, there are often separate monitors for the vocalists and instrumentalists. In most clubs and larger venues, sound engineers and technicians control the mixing boards for the "main" and "monitor" systems, adjusting the tone, sound levels, and overall volume of the performance.
Larger clubs and concert venues typically use a more complex type of monitor system which has two or three different monitor mixes for the different performers. Each monitor mix contains a blend of different vocal and instruments, and an amplified speaker is placed in front of the performer. This way the lead vocalist can have a mix which forefronts their vocals, the backup singers can have a mix which emphasizes their backup vocals, and the rhythm section members can have a mix which emphasizes the bass and drums. At an outdoor rock concert, there may be several thousand watts of power going to a complex monitor system that includes wedge-shaped cabinets for vocalists and larger cabinets called "sidefill" cabinets to help the musicians to hear their playing and singing. In the 2000s, major professional bands and singers often use small "in ear"-style headphone monitors rather than onstage monitor speakers.
In the early 1960s, many pop and rock concerts were performed without monitor speakers. In the early 1960s, PA systems were typically low-powered units which could only be used for the vocals. The PA systems during this era were not used to amplify the electric instruments on stage; each performer was expected to bring a powerful amplifier and speaker system to make their electric guitar, electric bass, Hammond organ or electric piano loud enough to hear onstage and to fill the venue with sound. Since many early 1960s PA systems did not have monitors, singers could only hear their vocals by listening to the reflected sound from the audience-facing "front of house" speakers after it bounced back from the rear wall of the venue. This was not an effective way to hear one's vocals, though, because the sound you hear bouncing back from the rear wall of the venue is late. Because singers could not hear their vocals, it made it hard to sing in rhythm with the band and in tune.
During the 1960s, many professional live sound engineers were wrestling with the problem of how to give singers enough volume of their own voice to stay in tune and in time during a performance. The use of performer-facing loudspeakers for foldback or monitoring may have been developed independently by sound engineers in different cities who were trying to resolve this problem. The first recorded time that a loudspeaker was used for foldback (monitoring) was for Judy Garland at the San Francisco Civic Auditorium on September 13, 1961; provided by McCune Sound Service. Bob Cavin, then an engineer at McCune Sound, designed the first monitor mixer designed expressly for foldback duties. He also designed the first stage monitor loudspeaker that had two different listening angles, for performers standing at the loudspeaker and for performers who were further away.
With the introduction of monitor speakers, it made it much easier for performers to hear their singing and playing on stage, which helped to improve the quality of live performances. Singers who can hear their singing clearly through monitor speakers can sing more in tune and more in rhythm with the backup band. As well, a singer who has a good monitor system does not have to "oversing" or strain her/his voice to try be heard. Monitor systems also helped rhythm section instrumentalists to improve their playing. With a good onstage monitoring system, even if there is a huge stage (e.g., at a stadium rock concert), and the musicians are far apart, the keyboardist can have a monitor speaker which reproduces the bass, rhythm guitar and drums, which helps her to play more in rhythm with the other band members.
From the late 1960s to the 1980s, most monitor speaker cabinets used an external power amplifier. In the 1990s and 2000s, clubs increasingly used powered monitors, which contain an integrated power amplifier. Most monitor speakers include an L pad, a potentiometer (knob) for controlling the volume of the horn. Another trend of the 2000s was the blurring of the lines between monitor speaker cabinets and regular speaker cabinets; many companies began selling wedge-shaped full-range speakers intended to be used for either monitors or main public address purposes. The introduction of generic stage speakers provides sound engineers with more flexibility to make changes to the sound system set-up, because if a venue has 10 generic "front of house"/monitor speakers, if the sound check reveals that the three monitor speakers are not providing enough monitoring volume (even at their maximum level), then the sound engineer can take one of the "front of house" speakers and put it on stage as an additional monitor.
Hardshell headphones are typically used by the sound board operator to listen to specific channels or to listen to the entire mix. While an amplified monitor speaker can also be used for this purpose, the high sound volumes in many club settings make hardshell headphones a better choice, because the hard plastic shell and foam cushions help to block the room noise. Some performers may use headphones as monitors, such as drummers in pop music bands.
In the 2000s, some bands and singers, typically touring professionals, began using small "in ear"-style headphone monitors. In-ear monitors allow musicians to hear their voice and the other instruments with a clearer, more intelligible sound, because the molded in-ear headphone design blocks out on-stage noise. While some in-ear monitors are "universal fit" designs, some companies also sell custom-made in-ear monitors, which require a fitting by an audiologist. Custom-made in-ear monitors provide an exact fit for a performer's ear. In-ear monitors greatly reduce on-stage volume by eliminating the need for on-stage monitor wedges. This reduced on-stage volume makes it easier for the Front of House audio engineer to get a good sound for the audience. In-ear monitors also make audio feedback "howls" much less likely, since there are no monitor speakers. The lower on-stage volume may lead to less hearing damage for performers. One drawback of in-ear monitors is that the singers and musicians cannot hear on-stage comments spoken away from a microphone (e.g., the bandleader turning away from the vocal mic and looking at the band and calling for an impromptu repetition of the chorus) or sounds from the audience. This issue can be rectified by placing microphones in front of the stage so that the band can hear the audience.
Drummers typically use a monitor speaker that is capable of loud bass reproduction, so that they can monitor their bass drum. However, having a 15" or even 18" subwoofer producing a high sound pressure level can raise the overall stage volumes to uncomfortable levels for the drummer, since the drums are already very loud. Since much very low bass is felt, some drummers use tactile transducers called "bass shakers", "butt shakers" and "throne shakers" to monitor the timing of their bass drum. The tactile transducers are attached to the drummer's stool ("throne") and the vibrations of the driver are transmitted to the body and then on to the ear in a manner similar to bone conduction. They connect to an amplifier like a normal subwoofer. They can be attached to a large flat surface (for instance a floor or platform) to create a large low frequency conduction area, although the transmission of low frequencies through the feet isn't as efficient as the seat. This helps the concert drummer to monitor his or her kick drum performance without "polluting" the stage with powerful low frequency waves from a subwoofer monitor.
The term "foldback" is sometimes applied to in-ear monitoring systems, also described as artist's cue-mixes, as they are generally set up for individual performers. "Foldback" may less frequently refer to current limiting protection in audio electronic amplifiers.
The term foldback has been used when referring to one or more video monitors facing a stage, in the same manner as an audio foldback monitor. The video monitor allows a person on stage to see what is behind them on screen, to see distant parties during a video conference, or to read notes or sing lyrics to a song. Other terms for this usage are confidence monitor and kicker monitor.