A sound reinforcement system is the combination of microphones, signal processors, amplifiers, and loudspeakers in enclosures all controlled by a mixing console that makes live or pre-recorded sounds louder and may also distribute those sounds to a larger or more distant audience. In many situations, a sound reinforcement system is also used to enhance or alter the sound of the sources on the stage, typically by using electronic effects, such as reverb, as opposed to simply amplifying the sources unaltered.
A sound reinforcement system for a rock concert in a stadium may be very complex, including hundreds of microphones, complex live sound mixing and signal processing systems, tens of thousands of watts of amplifier power, and multiple loudspeaker arrays, all overseen by a team of audio engineers and technicians. On the other hand, a sound reinforcement system can be as simple as a small public address (PA) system, consisting of, for example, a single microphone connected to a 100-watt amplified loudspeaker for a singer-guitarist playing in a small coffeehouse. In both cases, these systems reinforce sound to make it louder or distribute it to a wider audience.
Some audio engineers and others in the professional audio industry disagree over whether these audio systems should be called sound reinforcement (SR) systems or PA systems. Distinguishing between the two terms by technology and capability is common, while others distinguish by intended use (e.g., SR systems are for live event support and PA systems are for reproduction of speech and recorded music in buildings and institutions). In some regions or markets, the distinction between the two terms is important, though the terms are considered interchangeable in many professional circles.
Basic concept
A typical sound reinforcement system consists of; input transducers (e.g., microphones), which convert sound energy such as a person singing into an electric signal, signal processors which alter the signal characteristics (e.g., equalizers that adjust the bass and treble, compressors that reduce signal peaks, etc.), amplifiers, which produce a powerful version of the resulting signal that can drive a loudspeaker and output transducers (e.g., loudspeakers in speaker cabinets), which convert the signal back into sound energy (the sound heard by the audience and the performers). These primary parts involve varying numbers of individual componentsAudio Systems - Loudspeakers, Amplifiers, Signal Processors, Mixers, Music Source & Microphones . Retrieved on 2024-07-24. to achieve the desired goal of reinforcing and clarifying the sound to the audience, performers, or other individuals.
Signal path Sound reinforcement in a large format system typically involves a signal path that starts with the signal inputs, which may be instrument pickups (on an electric guitar or electric bass) or a microphone that a vocalist is singing into or a microphone placed in front of an instrument or guitar amplifier. These signal inputs are plugged into the input jacks of a thick multicore cable (often called a snake). The snake then delivers the signals of all of the inputs to one or more mixing consoles.
In a coffeehouse or small nightclub, the snake may be only routed to a single mixing console, which an audio engineer will use to adjust the sound and volume of the onstage vocals and instruments that the audience hears through the main speakers and adjust the volume of the monitor speakers that are aimed at the performers.
Mid- to large-size performing venues typically route the onstage signals to two mixing consoles: the front of house (FOH), and the stage monitor system, which is often a second mixer at the side of the stage. In these cases, at least two audio engineers are required; one to do the main mix for the audience at FOH and another to do the monitor mix for the performers on stage.
Once the signal arrives at an input on a mixing console, this signal can be adjusted in many ways by the sound engineer. A signal can be equalized (e.g., by adjusting the bass or treble of the sound), compressed (to avoid unwanted signal peaks), or panned (that is sent to the left or right speakers). The signal may also be routed into an external effects processor, such as a reverb effect, which outputs a wet (effected) version of the signal, which is typically mixed in varying amounts with the dry (effect-free) signal. Many electronic effects units are used in sound reinforcement systems, including digital delay and reverb. Some concerts use pitch correction effects (e.g., AutoTune), which electronically correct any out-of-tune singing.
Mixing consoles also have additional sends, also referred to as auxes or aux sends (an abbreviation for "auxiliary send"), on each input channel so that a different mix can be created and sent elsewhere for another purpose. One usage for aux sends is to create a mix of the vocal and instrument signals for the monitor mix (this is what the onstage singers and musicians hear from their monitor speakers or in-ear monitors). Another use of an aux send is to select varying amounts of certain channels (via the aux send knobs on each channel), and then route these signals to an effects processor. A common example of the second use of aux sends is to send all of the vocal signals from a rock band through a reverb effect. While reverb is usually added to vocals in the main mix, it is not usually added to electric bass and other rhythm section instruments.
The processed input signals are then mixed to the master faders on the console. The next step in the signal path generally depends on the size of the system in place. In smaller systems, the main outputs are often sent to an additional equalizer, or directly to a power amplifier, with one or more loudspeakers (typically two, one on each side of the stage in smaller venues, or a large number in big venues) that are connected to that amplifier. In large-format systems, the signal is typically first routed through an equalizer then to a crossover. A crossover splits the signal into multiple frequency bands with each band being sent to separate amplifiers and speaker enclosures for low, middle, and high-frequency signals. Low-frequency signals are sent to amplifiers and then to subwoofers, and middle and high-frequency sounds are typically sent to amplifiers which power full-range speaker cabinets. Using a crossover to separate the sound into low, middle and high frequencies can lead to a "cleaner", clearer sound (see bi-amplification) than routing all of the frequencies through a single full-range speaker system. Nevertheless, many small venues still use a single full-range speaker system, as it is easier to set up and less expensive.
System components
Input transducers
Many types of input transducers can be found in a sound reinforcement system, with microphones being the most commonly used input device. Microphones can be classified according to their method of transduction, polar pattern or their functional application. Most microphones used in sound reinforcement are either dynamic or condenser microphones. One type of directional microphone, called cardioid mics, are widely used in live sound, because they reduce pickup from the side and rear, helping to avoid unwanted feedback from the stage monitor system.
Microphones used for sound reinforcement are positioned and mounted in many ways, including base-weighted upright stands, podium mounts, tie-clips, instrument mounts, and headset mounts. Microphones on stands are also placed in front of instrument amplifiers to pick up the sound. Headset-mounted and tie-clip-mounted microphones are often used with wireless transmission to allow performers or speakers to move freely. Early adopters of headset mounted microphones technology included country singer Garth Brooks, Kate Bush, and Madonna.
Other types of input transducers include magnetic pickups used in electric guitars and electric basses, contact microphones used on stringed instruments, and pianos and phonograph pickups (cartridges) used in record players. Electronic instruments such as synthesizers can have their output signal routed directly to the mixing console. A DI unit may be necessary to adapt some of these sources to the inputs of the console.
Wireless Wireless systems are typically used for electric guitar, bass, handheld microphones and in-ear monitor systems. This lets performers move about the stage during the show or even go out into the audience without the worry of tripping over or disconnecting cables.
Mixing consoles
Mixing consoles are core to a sound reinforcement system. This is where the sound engineer can adjust the volume and tone of each input, whether it is a vocalist's microphone or the signal from an electric bass, and mix, equalize and add effects to these sound sources. Doing the mixing for a live show requires a mix of technical and artistic skills. A sound engineer needs to have an expert knowledge of speaker and amplifier set-up, effects units and other technologies and a good ear for what the music should sound like in order to create a good mix.
Multiple consoles can be used for different purposes in a single sound reinforcement system. The front-of-house (FOH) mixing console is typically located where the operator can see the action on stage and hear what the audience hears. For broadcast and recording applications, the mixing console may be placed within an enclosed booth or outside in an OB van. Large music productions often use a separate stage monitor mixing console which is dedicated to creating mixes for the performers on-stage. These consoles are typically placed at the side of the stage so that the operator can communicate with the performers on stage.
Signal processors Small PA systems for venues such as bars and clubs are now available with features that were formerly only available on professional-level equipment, such as digital reverb effects, graphic equalizers, and, in some models, feedback prevention circuits which electronically sense and prevent audio feedback when it becomes a problem. Digital effects units may offer multiple pre-set and variable reverb, echo and related effects. Digital loudspeaker management systems offer sound engineers digital delay (to ensure speakers are in sync with each other), limiting, crossover functions, EQ filters, compression and other functions in a single rack-mountable unit. In previous decades, sound engineers typically had to transport a substantial number of rack-mounted analog effects unit devices to accomplish these tasks.
Equalizers
Equalizers are electronic devices that allow audio engineers to control the tone and frequencies of the sound in a channel, group (e.g., all the mics on a drumkit) or an entire stage's mix. The bass and treble controls on a home stereo are a simple type of equalizer. Equalizers exist in professional sound reinforcement systems in three forms: shelving equalizers (typically for a whole range of bass and treble frequencies), graphic equalizers and parametric equalizers. Graphic equalizers have faders (vertical slide controls) which together resemble a frequency response curve plotted on a graph. The faders can be used to boost or cut specific frequency bands.