Stage monitor system
A stage monitor system is a set of performer-facing loudspeakers called monitor speakers, stage monitors, floor monitors, wedges, or foldbacks on stage during live music performances in which a sound reinforcement system is used to amplify a performance for the audience. The monitor system allows musicians to hear themselves and fellow band members clearly.
This article is about onstage monitor speakers for live performances. For studio reference loudspeakers, see studio monitor. For other uses of "foldback", see foldback (disambiguation).
The sound at popular music and rock music concerts is amplified with power amplifiers through a 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 amplifies the onstage sounds for the main audience. The monitor system is driven by a mix separate from the front-of-house system. This mix typically highlights the vocals and acoustic instruments so they can be heard over the electronic instruments and drums.[1][2]
Monitor systems have a range of sizes and complexity. A small pub or nightclub may have a single monitor speaker on stage so that the lead vocalist can hear their singing and the signal for the monitor may be produced on the same mixing console and audio engineer as the front-of-house mix. A stadium rock concert may use a large number of monitor wedges and a separate mixing console and engineer on or beside the stage for the monitors. 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 choose to hear mostly their voice in the monitor in front of them and the guitarist can choose to hear mostly the bassist and drummer in their monitor.
Monitor equipment[edit]
Monitor speakers[edit]
Monitor speakers often include a single full-range loudspeaker and a horn in a cabinet. Monitor speakers have numerous features that facilitate their transportation and protection, including handles, metal corner protectors, sturdy felt covering or paint and a metal grille to protect the speaker. Monitor speakers are normally heavy-duty speakers that can accept high input power to create high volumes and withstand extreme electrical and physical abuse.
There are two types of monitors: passive monitors consist of a loudspeaker and horn in a cabinet and 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 console can be plugged straight into the monitor speaker.
A recent trend has been to build the amplifier and associated sound processing equipment into the monitor speaker enclosure. These monitors are called active or powered monitors. This design allows amplifiers with the right amount of power to be custom made for the speakers. Active monitors are typically bi-amped and have an active crossover with custom equalization to tune the monitor to have a flat frequency response. One of the first examples of this type of monitor is the Meyer Sound Laboratories UM-1P.[9]
Monitor speakers come in two forms: floor monitors and side-fill monitors.
Floor monitors are compact speakers with an angled back that is laid on the floor. This angled shape gives the floor monitor its other name of wedge. The angle is typically 30 degrees which points the speaker back and up towards the performer. These speakers may also be single small speakers which are sometimes mounted on a microphone stand to get them closer to the performers' ears. More often they are heavy-duty two-way systems with a woofer and a high-frequency horn. A small floor monitor might use a 12" woofer with an integrated high-frequency horn or driver combination.[10] A large floor monitor might use one or two 15" woofers and a high-frequency driver attached to a high-frequency horn.[11] The speaker might use a passive crossover or might be bi-amped with an active crossover and separate amplifiers for the woofer and high-frequency driver.
Side-fill monitors are monitors that sit upright on the side of the stage and are used to provide sound to the areas of the stage not covered by the floor monitors. Side fill monitors are typically standard FOH speakers. A special case of a side fill monitor is a drum fill. Drum fills are typically large 2- or 3-way speakers with one or more large woofers capable of extremely high volumes to help drummers hear other band members over the acoustic sound of their drums.
Monitor amplifiers[edit]
If the amplifier is not built into the monitor speaker enclosure, one or more external amplifiers are required to power the monitor system speakers. Robust commercial amplifiers are used here. In a simple monitor system, a single amplifier may drive all monitor speakers. In more complex scenarios where there are multiple monitor mixes, additional power is required or speakers are bi-amped, multiple amplifiers or amplifier channels are used.
Equalization and signal processing[edit]
Monitor speakers need their own equalization primarily to reduce or eliminate acoustic feedback. Acoustic feedback occurs when the time delay between the acoustic input of a microphone and the output of a monitor speaker is a multiple of the period of a frequency. When this occurs the acoustic output of the speaker is picked up by the microphone and amplified again by the monitor speaker. This is a positive feedback loop that reinforces the specific frequency, causing the speaker to howl or squeal. Equalization is used to attenuate the specific frequency that is feeding back.
The process of eliminating feedback in the monitor is called ringing out the monitors. To eliminate feedback, the monitor's level is increased until it starts to feed back. The feedback frequency is identified either by ear or by a frequency analyzer. Equalization is used to reduce that frequency. The monitor level is again increased until the next frequency starts to feed back and that frequency is eliminated. The process is repeated until feedback occurs at a previously suppressed frequency or at multiple frequencies simultaneously. If multiple monitor mixes are being used, the process has to be repeated for each separate monitor mix.[12]