Monitor speakers often include a single full-range loudspeaker and a horn in a cabinet. The sound at popular music and rock concerts is amplified with power amplifiers through a PA system or sound reinforcement system. With the exception of the smallest venues, such as coffeehouses, the main or front of house 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 performers rather than the audience. Monitor systems have a range of sizes and complexity. In most mid- to large-size venues, there is a sound engineer. The monitor mix is different from the front of house mix. In the most sophisticated and expensive monitor set-ups, each onstage performer can ask the engineer for a separate monitor mix for separate monitors. For example, the singer can ask to hear mostly her/his voice in the monitor in front of her/him. Without a foldback system, the sound that on-stage performers would hear from front of house would be the reverberated reflections bouncing from the wall of the venue. The naturally reflected sound is delayed and distorted, which could, for example, in situations with poor or absent foldback mixes, vocalists may end up singing off-tune or out of time with the band. Each system consists of a board, sound processing equipment, power amplifiers. 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 systems or Public Address systems. This distinction is important in regions or markets, while in other regions or markets the terms are interchangeable. 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 performers, to help them hear the instruments. The monitor system in a coffeehouse or singer-songwriter stage for a bar may be a single 100 watt powered monitor wedge. In the smallest PA systems, the performer may set their own main, 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
A JBL floor monitor speaker cabinet with a 12" woofer and a "bullet" tweeter. Typically, the speaker would be covered with a metal grille to protect it.
This small venue's stage shows an example of a typical monitor speaker set-up: there are three "wedge" monitors directed towards the area of the stage where singers and instrumentalists will be performing. The drummer has both a subwoofer cabinet (for monitoring the bass drum and the electric bass) and a "wedge"-style cabinet for monitoring vocals and mid- or high-frequency sounds.
A rock band stage clearly shows the stage monitors.
A picture of in-ear monitors, also known as canalphones, which are used by on-stage performers. This particular model is the Etymotic ER-4S