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A sound reinforcement system is the combination of
microphone A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and publ ...
s, signal processors,
amplifier An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It may increase the power significantly, or its main effect may be to boost t ...
s, and
loudspeaker A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A ''speaker system'', also often simply referred to as a "speaker" or ...
s in
enclosures Enclosure or Inclosure is a term, used in English landownership, that refers to the appropriation of "waste" or "common land" enclosing it and by doing so depriving commoners of their rights of access and privilege. Agreements to enclose land ...
all controlled by a
mixing console A mixing console or mixing desk is an electronic device for Audio mixing (recorded music), mixing audio signals, used in sound recording and reproduction and sound reinforcement systems. Inputs to the console include microphones, signals fro ...
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 An electronic effect influences the structure, reactivity, or properties of molecule but is neither a traditional bond nor a steric effect. In organic chemistry, the term stereoelectronic effect is also used to emphasize the relation between th ...
, such as
reverb Reverberation (also known as reverb), in acoustics, is a persistence of sound, after a sound is produced. Reverberation is created when a sound or signal is reflected causing numerous reflections to build up and then decay as the sound is abs ...
, as opposed to simply amplifying the sources unaltered. A sound reinforcement system for a
rock concert A rock concert is a performance of rock music. During the 1950s, several American musical groups experimented with new musical forms that fused country music, blues, and swing genre to produce the earliest examples of "rock and roll." The coin ...
in a stadium may be very complex, including hundreds of microphones, complex
live sound mixing Live sound mixing is the blending of multiple sound sources by an audio engineer using a mixing console or software. Sounds that are mixed include those from instruments and voices which are picked up by microphones (for drum kit, lead vocals an ...
and signal processing systems, tens of thousands of
watt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James ...
s of
amplifier An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It may increase the power significantly, or its main effect may be to boost t ...
power, and multiple loudspeaker arrays, all overseen by a team of
audio engineer An audio engineer (also known as a sound engineer or recording engineer) helps to produce a recording or a live performance, balancing and adjusting sound sources using equalization, dynamics processing and audio effects, mixing, reproduction ...
s and technicians. On the other hand, a sound reinforcement system can be as simple as a small
public address A public address system (or PA system) is an electronic system comprising microphones, amplifiers, loudspeakers, and related equipment. It increases the apparent volume (loudness) of a human voice, musical instrument, or other acoustic sound sou ...
(PA) system, consisting of, for example, a single microphone connected to a 100-watt
amplified loudspeaker Powered speakers, also known as self-powered speakers and active speakers, are loudspeakers that have built-in amplifiers. Powered speakers are used in a range of settings, including in sound reinforcement systems (used at live music concerts), ...
for a singer-guitarist playing in a small
coffeehouse A coffeehouse, coffee shop, or café is an establishment that primarily serves coffee of various types, notably espresso, latte, and cappuccino. Some coffeehouses may serve cold drinks, such as iced coffee and iced tea, as well as other non-ca ...
. 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 Professional audio, abbreviated as pro audio, refers to both an activity and a category of high quality, studio-grade audio equipment. Typically it encompasses sound recording, sound reinforcement system setup and audio mixing, and studio mu ...
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 Live event support includes staging, scenery, mechanicals, sound, lighting, video, special effects, transport, packaging, communications, costume and makeup for live performance events including theater, music, dance, and opera. They all share th ...
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
transducer A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and con ...
s (e.g.,
microphone A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and publ ...
s), which convert
sound energy In physics, sound energy is a form of energy that can be heard by living things. Only those waves that have a frequency of 16 Hz to 20 kHz are audible to humans. However, this range is an average and will slightly change from individ ...
such as a person
singing Singing is the act of creating musical sounds with the voice. A person who sings is called a singer, artist or vocalist (in jazz and/or popular music). Singers perform music ( arias, recitatives, songs, etc.) that can be sung with or ...
into an electric signal, signal processors which alter the signal characteristics (e.g., equalizers that adjust the bass and treble,
compressors A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor. Compressors are similar to pumps: both increase the pressure on a fluid and both can trans ...
that reduce signal peaks, etc.),
amplifier An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It may increase the power significantly, or its main effect may be to boost t ...
s, which produce a powerful version of the resulting signal that can drive a
loudspeaker A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A ''speaker system'', also often simply referred to as a "speaker" or ...
and output transducers (e.g., loudspeakers in
speaker cabinet A loudspeaker enclosure or loudspeaker cabinet is an enclosure (often rectangular box-shaped) in which speaker drivers (e.g., loudspeakers and tweeters) and associated electronic hardware, such as crossover circuits and, in some cases, power ...
s), 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 componentsSound Equipment - Loudspeakers, Amplifiers, Signal Processors, Mixers, Music Source & Microphones
. Retrieved on 2011-12-11.
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 An electric guitar is a guitar that requires external amplification in order to be heard at typical performance volumes, unlike a standard acoustic guitar (however combinations of the two - a semi-acoustic guitar and an electric acoustic gu ...
or
electric bass The bass guitar, electric bass or simply bass (), is the lowest-pitched member of the string family. It is a plucked string instrument similar in appearance and construction to an electric or an acoustic guitar, but with a longer neck and s ...
) or a microphone that a vocalist is singing into or a microphone placed in front of an instrument or
guitar amplifier A guitar amplifier (or amp) is an electronic device or system that strengthens the electrical signal from a pickup on an electric guitar, bass guitar, or acoustic guitar so that it can produce sound through one or more loudspeakers, which ar ...
. These signal inputs are plugged into the input jacks of a thick
multicore cable A multicore cable is a type of electrical cable that combines multiple signals or power feeds into a single jacketed cable. The term is normally only used in relation to a cable that has more cores than commonly encountered. Not all cables with mu ...
(often called a ''snake''). The snake then delivers the signals of all of the inputs to one or more
mixing console A mixing console or mixing desk is an electronic device for Audio mixing (recorded music), mixing audio signals, used in sound recording and reproduction and sound reinforcement systems. Inputs to the console include microphones, signals fro ...
s. 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 console A mixing console or mixing desk is an electronic device for Audio mixing (recorded music), mixing audio signals, used in sound recording and reproduction and sound reinforcement systems. Inputs to the console include microphones, signals fro ...
s: the
front of house In the performing arts, front of house (FOH) is the part of a performance venue that is open to the public. In theatres and live music venues, it consists of the auditorium and foyers, as opposed to the stage and backstage areas. In a theatre, ...
(FOH), and the
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 ...
, which is often a second mixer at the side of the stage. In these cases, at least two
audio engineer An audio engineer (also known as a sound engineer or recording engineer) helps to produce a recording or a live performance, balancing and adjusting sound sources using equalization, dynamics processing and audio effects, mixing, reproduction ...
s 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 Reverberation (also known as reverb), in acoustics, is a persistence of sound, after a sound is produced. Reverberation is created when a sound or signal is reflected causing numerous reflections to build up and then decay as the sound is abs ...
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 unit An effects unit or effects pedal is an electronic device that alters the sound of a musical instrument or other audio source through audio signal processing. Common effects include distortion/overdrive, often used with electric guitar in ...
s are used in sound reinforcement systems, including
digital delay A digital delay line is a discrete element in digital filter theory, which allows a signal to be delayed by a number of samples. If the delay is an integer multiple of samples, digital delay lines are often implemented as circular buffers. This me ...
and
reverb Reverberation (also known as reverb), in acoustics, is a persistence of sound, after a sound is produced. Reverberation is created when a sound or signal is reflected causing numerous reflections to build up and then decay as the sound is abs ...
. Some concerts use pitch correction effects (e.g.,
AutoTune Auto-Tune (or autotune) is an audio processor introduced in 1996 by American company Antares Audio Technologies. Auto-Tune uses a proprietary device to measure and alter pitch in vocal and instrumental music recording and performances. Auto-T ...
), 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 monitor In-ear monitors (IEMs) are devices used by musicians, audio engineers and audiophiles to listen to music or to hear a personal mix of vocals and stage instrumentation for live performance or recording studio mixing. They are also used by telev ...
s). 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 A rock band or pop band is a small musical ensemble that performs rock music, pop music, or a related genre. A four-piece band is the most common configuration in rock and pop music. In the early years, the configuration was typically two gui ...
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 A rhythm section is a group of musicians within a music ensemble or band that provides the underlying rhythm, harmony and pulse of the accompaniment, providing a rhythmic and harmonic reference and "beat" for the rest of the band. The rhyth ...
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 An audio power amplifier (or power amp) is an electronic amplifier that amplifies low-power electronic audio signals, such as the signal from a radio receiver or an electric guitar pickup, to a level that is high enough for driving louds ...
, 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 Crossover may refer to: Entertainment Albums and songs * ''Cross Over'' (Dan Peek album) * ''Crossover'' (Dirty Rotten Imbeciles album), 1987 * ''Crossover'' (Intrigue album) * ''Crossover'' (Hitomi Shimatani album) * ''Crossover'' (Yoshino ...
. 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
subwoofer A subwoofer (or sub) is a loudspeaker designed to reproduce low-pitched audio frequencies known as bass and sub-bass, lower in frequency than those which can be (optimally) generated by a woofer. The typical frequency range for a subwoofer i ...
s, and middle and high-frequency sounds are typically sent to amplifiers which power full-range
speaker Speaker may refer to: Society and politics * Speaker (politics), the presiding officer in a legislative assembly * Public speaker, one who gives a speech or lecture * A person producing speech: the producer of a given utterance, especially: ** In ...
cabinets. Using a crossover to separate the sound into low, middle and high frequencies can lead to a "cleaner", clearer sound (see
bi-amplification Bi-amping and tri-amping is the practice of using two or three audio amplifiers to amplify different audio frequency ranges, with the amplified signals being routed to different speaker drivers, such as woofers, subwoofers and tweeters. Biampin ...
) 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
transducer A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and con ...
s can be found in a sound reinforcement system, with
microphone A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and publ ...
s 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 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 ...
. 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 amplifier An instrument amplifier is an electronic device that converts the often barely audible or purely electronic signal of a musical instrument into a larger electronic signal to feed to a loudspeaker. An instrument amplifier is used with musical ins ...
s 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 Troyal Garth Brooks (born February 7, 1962) is an American country music singer and songwriter. His integration of pop and rock elements into the country genre has earned him popularity, particularly in the United States with success on the co ...
,
Kate Bush Catherine Bush (born 30 July 1958) is an English singer, songwriter, record producer and dancer. In 1978, at the age of 19, she topped the UK Singles Chart for four weeks with her debut single " Wuthering Heights", becoming the first female ...
, and
Madonna Madonna Louise Ciccone (; ; born August 16, 1958) is an American singer-songwriter and actress. Widely dubbed the " Queen of Pop", Madonna has been noted for her continual reinvention and versatility in music production, songwriting, a ...
. Other types of input transducers include magnetic pickups used in electric guitars and electric basses,
contact microphone A contact microphone, also known as a piezo microphone, is a form of microphone that senses audio vibrations through contact with solid objects. Unlike normal air microphones, contact microphones are almost completely insensitive to air vibrat ...
s used on stringed instruments, and pianos and
phonograph A phonograph, in its later forms also called a gramophone (as a trademark since 1887, as a generic name in the UK since 1910) or since the 1940s called a record player, or more recently a turntable, is a device for the mechanical and analogu ...
pickups (cartridges) used in record players. Electronic instruments such as
synthesizer A synthesizer (also spelled synthesiser) is an electronic musical instrument that generates audio signals. Synthesizers typically create sounds by generating waveforms through methods including subtractive synthesis, additive synthesis a ...
s can have their output signal routed directly to the mixing console. A
DI unit A DI unit (direct input or direct inject) is an electronic device typically used in recording studios and in sound reinforcement systems to connect a high- output impedance, line level, unbalanced output signal to a low-impedance, microphone leve ...
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 console A mixing console or mixing desk is an electronic device for Audio mixing (recorded music), mixing audio signals, used in sound recording and reproduction and sound reinforcement systems. Inputs to the console include microphones, signals fro ...
s are the heart of 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 The bass guitar, electric bass or simply bass (), is the lowest-pitched member of the string family. It is a plucked string instrument similar in appearance and construction to an electric or an acoustic guitar, but with a longer neck and s ...
, 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 unit An effects unit or effects pedal is an electronic device that alters the sound of a musical instrument or other audio source through audio signal processing. Common effects include distortion/overdrive, often used with electric guitar in ...
s 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 Reverberation (also known as reverb), in acoustics, is a persistence of sound, after a sound is produced. Reverberation is created when a sound or signal is reflected causing numerous reflections to build up and then decay as the sound is abs ...
effects,
graphic equalizer Equalization, or simply EQ, in sound recording and reproduction is the process of adjusting the volume of different frequency bands within an audio signal. The circuit or equipment used to achieve this is called an equalizer. Most hi-fi eq ...
s, and, in some models,
feedback prevention A feedback suppressor is an audio signal processing device which is used in the signal path in a live sound reinforcement system to prevent or suppress audio feedback. Digital feedback reduction is the application of digital techniques to sound re ...
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 An effects unit or effects pedal is an electronic device that alters the sound of a musical instrument or other audio source through audio signal processing. Common effects include distortion/overdrive, often used with electric guitar in ...
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 Home audio systems are audio electronics intended for home entertainment use, such as shelf stereos, music centres and surround sound receivers. Home audio generally does not include standard equipment such as built-in television speakers, but r ...
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 equalizer Equalization, or simply EQ, in sound recording and reproduction is the process of adjusting the volume of different frequency bands within an audio signal. The circuit or equipment used to achieve this is called an equalizer. Most hi-fi eq ...
s and
parametric equalizer Equalization, or simply EQ, in sound recording and reproduction is the process of adjusting the volume of different frequency bands within an audio signal. The circuit or equipment used to achieve this is called an equalizer. Most hi-fi eq ...
s. 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. Using equalizers, frequencies which are too weak, such as a singer with modest projection in their lower register, can be boosted. Frequencies which are too loud, such as a "boomy" sounding
bass drum The bass drum is a large drum that produces a note of low definite or indefinite pitch. The instrument is typically cylindrical, with the drum's diameter much greater than the drum's depth, with a struck head at both ends of the cylinder. Th ...
, or an overly resonant
dreadnought guitar The dreadnought is a type of acoustic guitar body developed by American guitar manufacturer C.F. Martin & Company. The style, since copied by other guitar manufacturers, has become the most common for acoustic guitars. At the time of its creat ...
can be cut. Sound reinforcement systems typically use graphic equalizers with one-third
octave In music, an octave ( la, octavus: eighth) or perfect octave (sometimes called the diapason) is the interval between one musical pitch and another with double its frequency. The octave relationship is a natural phenomenon that has been refer ...
frequency centers. These are typically used to equalize output signals going to the main loudspeaker system or the monitor speakers on stage. Parametric equalizers are often built into each channel in mixing consoles, typically for the mid-range frequencies. They are also available as separate rack-mount units which can be connected to a mixing board. Parametric equalizers typically use knobs and sometimes buttons. The audio engineer can select which frequency band to cut or boost, and then use additional knobs to adjust how much to cut or boost this frequency range. Parametric equalizers first became popular in the 1970s and have remained the program equalizer of choice for many engineers since then. A high-pass (low-cut) and/or
low-pass A low-pass filter is a filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. The exact frequency response of the filter depends on the filte ...
(high-cut) filter may also be included on equalizers or audio consoles. High-pass and low-pass filters restrict a given channel's
bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...
extremes. Cutting very low frequency sound signals (termed infrasonic, or ''subsonic'') reduces the waste of amplifier power which does not produce audible sound and which moreover can be hard on the low-range speakers. A low-pass filter to cut
ultrasonic Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies fr ...
energy is useful to prevent interference from radio frequencies, lighting control, or digital circuitry creeping into the power amplifiers. Such filters are often paired with graphic and parametric equalizers to give the audio engineer full control of the frequency range. High-pass filters and low-pass filters used together function as a
band-pass A band-pass filter or bandpass filter (BPF) is a device that passes frequencies within a certain range and rejects (attenuates) frequencies outside that range. Description In electronics and signal processing, a filter is usually a two-po ...
filter, eliminating undesirable frequencies both above and below the auditory spectrum. A
band-stop filter In signal processing, a band-stop filter or band-rejection filter is a filter that passes most frequencies unaltered, but attenuates those in a specific range to very low levels. It is the opposite of a band-pass filter. A notch filter is a ...
, does the opposite. It allows all frequencies to pass except for one band in the middle. A feedback suppressor, using an
microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circ ...
, automatically detects the onset of feedback and applies a narrow band-stop filter (a
notch filter In signal processing, a band-stop filter or band-rejection filter is a filter that passes most frequencies unaltered, but attenuates those in a specific range to very low levels. It is the opposite of a band-pass filter. A notch filter is a ...
) at specific frequency or frequencies pertaining to the feedback.


Compressors

Dynamic range compression Dynamic range compression (DRC) or simply compression is an audio signal processing operation that reduces the volume of loud sounds or amplifies quiet sounds, thus reducing or ''compressing'' an audio signal's dynamic range. Compression is ...
is designed to help the audio engineer to manage the dynamic range of audio signals. Prior to the invention of automatic compressors, audio engineers accomplished the same goal by "riding the faders", listening carefully to the mix and lowering the faders of any singer or instrument which was getting too loud. A compressor accomplishes this by reducing the gain of a signal that is above a defined level (the threshold) by a defined amount determined by the ratio setting. Most compressors available are designed to allow the operator to select a ratio within a range typically between 1:1 and 20:1, with some allowing settings of up to ∞:1. A compressor with high compression ratio is typically referred to as a
limiter In electronics, a limiter is a circuit that allows signals below a specified input power or level to pass unaffected while attenuating (lowering) the peaks of stronger signals that exceed this threshold. Limiting is a type of dynamic range comp ...
. The speed that the compressor adjusts the gain of the signal ( attack and release) is typically adjustable as is the final output or ''make-up gain'' of the device. Compressor applications vary widely. Some applications use limiters for component protection and gain structure control. Artistic signal manipulation using a compressor is a subjective technique widely utilized by mix engineers to improve clarity or to creatively alter the signal in relation to the program material. An example of artistic compression is the typical heavy compression used on the various components of a modern rock drum kit. The drums are processed to be perceived as sounding more punchy and full.


Noise gates

A
noise gate A noise gate or gate is an electronic device or software that is used to control the volume of an audio signal. Comparable to a compressor, which attenuates signals ''above'' a threshold, such as loud attacks from the start of musical notes, no ...
mutes signals below a set threshold level. A noise gate's function is in, a sense, opposite to that of a compressor. Noise gates are useful for microphones which will pick up noise that is not relevant to the program, such as the hum of a miked electric guitar amplifier or the rustling of papers on a minister's lectern. Noise gates are also used to process the microphones placed near the drums of a drum kit in many hard rock and metal bands. Without a noise gate, the microphone for a specific instrument such as the floor tom will also pick up signals from nearby drums or cymbals. With a noise gate, the threshold of sensitivity for each microphone on the drum kit can be set so that only the direct strike and subsequent decay of the drum will be heard, not the nearby sounds.


Effects

Reverberation Reverberation (also known as reverb), in acoustics, is a persistence of sound, after a sound is produced. Reverberation is created when a sound or signal is reflected causing numerous reflections to build up and then decay as the sound is abso ...
and
delay Delay (from Latin: dilatio) may refer to: Arts, entertainment, and media * ''Delay 1968'', a 1981 album by German experimental rock band Can * '' The Delay'', a 2012 Uruguayan film People * B. H. DeLay (1891–1923), American aviator and ac ...
effects are widely used in sound reinforcement systems to enhance the sound of the mix and create a desired artistic effect. Reverb and delay add a sense of spaciousness to the sound. Reverb can give the effect of singing voice or instrument being present in anything from a small room to a massive hall, or even in a space that does not exist in the physical world. The use of reverb often goes unnoticed by the audience, as it often sounds more natural than if the signal was left "dry" (without effects). Many modern mixing boards designed for live sound include on-board reverb effects. Other effects include modulation effects such as
Flanger Flanging is an audio signal processing, audio effect produced by mixing two identical audio signal, signals together, one signal delayed by a small and (usually) gradually changing period, usually smaller than 20 milliseconds. This produces a s ...
, phaser, and
chorus Chorus may refer to: Music * Chorus (song) or refrain, line or lines that are repeated in music or in verse * Chorus effect, the perception of similar sounds from multiple sources as a single, richer sound * Chorus form, song in which all verse ...
and spectral manipulation or harmonic effects such as the exciter and
harmonizer Pitch shifting is a sound recording technique in which the original pitch of a sound is raised or lowered. Effects units that raise or lower pitch by a pre-designated musical interval ( transposition) are called pitch shifters. Pitch and tim ...
. The use of effects in the reproduction of 2010-era pop music is often in an attempt to mimic the sound of the studio version of the artist's music in a live concert setting. For example, an audio engineer may use an
Auto Tune Auto-Tune (or autotune) is an audio processor introduced in 1996 by American company Antares Audio Technologies. Auto-Tune uses a proprietary device to measure and alter pitch in vocal and instrumental music recording and performances. Auto-Tu ...
effect to produce unusual vocal sound effects that a singer used on their recordings. The appropriate type, variation, and level of effects is quite subjective and is often collectively determined by a production's audio engineer, artists,
bandleader A bandleader is the leader of a music group such as a rock or pop band or jazz quartet. The term is most commonly used with a group that plays popular music as a small combo or a big band, such as one which plays jazz, blues, rhythm and blues o ...
,
music producer A record producer is a recording project's creative and technical leader, commanding studio time and coaching artists, and in popular genres typically creates the song's very sound and structure.Virgil Moorefield"Introduction" ''The Producer as ...
, or musical director.


Feedback suppressor

A
feedback suppressor A feedback suppressor is an audio signal processing device which is used in the signal path in a live sound reinforcement system to prevent or suppress audio feedback. Digital feedback reduction is the application of digital techniques to sound r ...
detects unwanted
audio feedback Audio feedback (also known as acoustic feedback, simply as feedback) is a positive feedback situation which may occur when an acoustic path exists between an audio input (for example, a microphone or guitar pickup) and an audio output (for exa ...
and suppresses it, typically by automatically inserting a
notch filter In signal processing, a band-stop filter or band-rejection filter is a filter that passes most frequencies unaltered, but attenuates those in a specific range to very low levels. It is the opposite of a band-pass filter. A notch filter is a ...
into the signal path of the system. Audio feedback can create unwanted loud, screaming noises that are disruptive to the performance, and can damage speakers and performers' and audience members' ears. Audio feedback from microphones occurs when a microphone is too near a monitor or main speaker and the sound reinforcement system amplifies itself. audio feedback through a microphone is almost universally regarded as a negative phenomenon, many
electric guitar An electric guitar is a guitar that requires external amplification in order to be heard at typical performance volumes, unlike a standard acoustic guitar (however combinations of the two - a semi-acoustic guitar and an electric acoustic gu ...
ists use guitar feedback as part of their performance. This type of feedback is intentional, so the sound engineer does not try to prevent it.


Power amplifiers

A
power amplifier An audio power amplifier (or power amp) is an electronic amplifier that amplifies low-power electronic audio signals, such as the signal from a radio receiver or an electric guitar pickup, to a level that is high enough for driving louds ...
is an electronic device that uses electrical power and circuitry to boost a
line level Line level is the specified strength of an audio signal used to transmit analog audio between components such as CD and DVD players, television sets, audio amplifiers, and mixing consoles. Line level sits between other levels of audio signal ...
signal and provides enough electrical power to drive a loudspeaker and produce sound. All loudspeakers, including
headphones Headphones are a pair of small loudspeaker drivers worn on or around the head over a user's ears. They are electroacoustic transducers, which convert an electrical signal to a corresponding sound. Headphones let a single user listen to an a ...
, require power amplification. Most professional audio power amplifiers also provide protection from
clipping Clipping may refer to: Words * Clipping (morphology), the formation of a new word by shortening it, e.g. "ad" from "advertisement" * Clipping (phonetics), shortening the articulation of a speech sound, usually a vowel * Clipping (publications) ...
typically as some form of limiting. A power amplifier pushed into clipping can damage loudspeakers. Amplifiers also typically provide protection against
short circuit A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circu ...
s across the output and overheating. Audio engineers select amplifiers that provide enough headroom. Headroom refers to the amount by which the signal-handling capabilities of an audio system exceed a designated
nominal level Nominal level is the operating level at which an electronic signal processing device is designed to operate. The electronic circuits that make up such equipment are limited in the maximum signal they can handle and the low-level internally genera ...
. Headroom can be thought of as a safety zone allowing transient audio peaks to exceed the nominal level without damaging the system or the audio signal, e.g., via
clipping Clipping may refer to: Words * Clipping (morphology), the formation of a new word by shortening it, e.g. "ad" from "advertisement" * Clipping (phonetics), shortening the articulation of a speech sound, usually a vowel * Clipping (publications) ...
. Standards bodies differ in their recommendations for nominal level and headroom. Selecting amplifiers with enough headroom helps to ensure that the signal will remain clean and undistorted. Like most sound reinforcement equipment, professional power amplifiers are typically designed to be mounted within standard
19-inch rack A 19-inch rack is a standardized frame or enclosure for mounting multiple electronic equipment modules. Each module has a front panel that is wide. The 19 inch dimension includes the edges or "ears" that protrude from each side of the equ ...
s. Rack-mounted amps are typically housed in
road case A road case, ATA case or flight case is a shipping container specifically built to protect musical instruments, motion picture equipment, audio and lighting production equipment, properties, firearms, or other sensitive equipment when it must be ...
s to prevent damage to the equipment during transportation. Active loudspeakers have internally mounted amplifiers that have been selected by the manufacturer to match the requirements of the loudspeaker. Some active loudspeakers also have equalization, crossover and mixing circuitry built in. Since amplifiers can generate a significant amount of heat, thermal dissipation is an important factor for operators to consider when mounting amplifiers into equipment racks. Many power amplifiers feature internal fans to draw air across their heat sinks. The heat sinks can become clogged with dust, which can adversely affect the cooling capabilities of the amplifier. In the 1970s and 1980s, most PAs employed heavy
class AB amplifier In electronics, power amplifier classes are letter symbols applied to different power amplifier types. The class gives a broad indication of an amplifier's characteristics and performance. The classes are related to the time period that the active ...
s. In the late 1990s, power amplifiers in PA applications became lighter, smaller, more powerful, and more efficient, with the increasing use of
switching power supplies A switched-mode power supply (switching-mode power supply, switch-mode power supply, switched power supply, SMPS, or switcher) is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently. Lik ...
and class D amplifiers, which offered significant weight- and space-savings as well as increased efficiency. Often installed in railroad stations, stadia, and airports, class D amplifiers can run with minimal additional cooling and with higher rack densities, compared to older amplifiers. Digital loudspeaker management systems (DLMS) that combine digital crossover functions, compression, limiting, and other features in a single unit are used to process the mix from the mixing console and route it to the various amplifiers. Systems may include several loudspeakers, each with its own output optimized for a specific range of frequencies (i.e. bass, midrange, and treble).
Bi-amping and tri-amping Bi-amping and tri-amping is the practice of using two or three audio amplifiers to amplify different audio frequency ranges, with the amplified signals being routed to different speaker drivers, such as woofers, subwoofers and tweeters. Biampin ...
of a sound reinforcement system with the aid of a DLMS results in more efficient use of amplifier power by sending each amplifier only the frequencies appropriate for its respective loudspeaker and eliminating losses associated with
passive crossover Audio crossovers are a type of electronic filter circuitry that splits an audio signal into two or more frequency ranges, so that the signals can be sent to loudspeaker drivers that are designed to operate within different frequency ranges. Th ...
circuits.


Main loudspeakers

A simple and inexpensive PA
loudspeaker A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A ''speaker system'', also often simply referred to as a "speaker" or ...
may have a single full-range
loudspeaker driver An electrodynamic speaker driver, often called simply a speaker driver when the type is implicit, is an individual transducer that converts an electrical audio signal to sound waves. While the term is sometimes used interchangeably with the ...
, housed in a suitable enclosure. More elaborate, professional-caliber sound reinforcement loudspeakers may incorporate separate drivers to produce low, middle, and high
frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
sounds. A crossover network routes the different frequencies to the appropriate drivers. In the 1960s, horn loaded theater and PA speakers were commonly columns of multiple drivers mounted in a vertical line within a tall enclosure. The 1970s to early 1980s was a period of innovation in loudspeaker design with many sound reinforcement companies designing their own speakers using commercially available drivers. The areas of innovation were in cabinet design, durability, ease of packing and transport, and ease of setup. This period also saw the introduction of the hanging or ''flying'' of main loudspeakers at large concerts. During the 1980s the large speaker manufacturers started producing standard products using the innovations of the 1970s. These were mostly smaller two way systems with 12", 15" or double 15" woofers and a high frequency driver attached to a high frequency horn. The 1980s also saw the start of loudspeaker companies focused on the sound reinforcement market. The 1990s saw the introduction of line arrays, where long vertical arrays of loudspeakers in smaller cabinets are used to increase efficiency and provide even dispersion and frequency response.
Trapezoidal A quadrilateral with at least one pair of parallel sides is called a trapezoid () in American and Canadian English. In British and other forms of English, it is called a trapezium (). A trapezoid is necessarily a convex quadrilateral in Eucli ...
-shaped enclosures became popular as this shape allowed many of them to be easily arrayed together. This period also saw the introduction of inexpensive molded plastic speaker enclosures mounted on tripod stands. Many feature built-in power amplifiers which made them practical for non-professionals to set up and operate successfully. The sound quality available from these simple
powered speakers Powered speakers, also known as self-powered speakers and active speakers, are loudspeakers that have built-in amplifiers. Powered speakers are used in a range of settings, including in sound reinforcement systems (used at live music concerts), bo ...
varies widely depending on the implementation. Many sound reinforcement loudspeaker systems incorporate protection circuitry to prevent damage from excessive power or operator error.
Resettable fuse A resettable fuse or polymeric positive temperature coefficient device (PPTC) is a passive electronic component used to protect against overcurrent faults in electronic circuits. The device is also known as a multifuse or polyfuse or polyswitch ...
s, specialized current-limiting light bulbs, and
circuit breaker A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by an overcurrent or short circuit. Its basic function is to interrupt current flow to protect equipment and to prevent the ris ...
s were used alone or in combination to reduce driver failures. During the same period, the professional sound reinforcement industry made the Neutrik
Speakon The Speakon (stylized speakON) is a trademarked name for an electrical connector, originally manufactured by Neutrik, mostly used in professional audio systems for connecting loudspeakers to amplifiers. Other manufacturers make compatible prod ...
NL4 and NL8 connectors the standard speaker connectors, replacing 1/4" jacks,
XLR connector The XLR connector is a type of electrical connector primarily used in professional audio, video, and stage lighting equipment. XLR connectors are cylindical in design, and have three to seven connector pins, and are often employed for analog b ...
s, and
Cannon A cannon is a large- caliber gun classified as a type of artillery, which usually launches a projectile using explosive chemical propellant. Gunpowder ("black powder") was the primary propellant before the invention of smokeless powder ...
multipin connectors which are all limited to a maximum of 15 amps of current. XLR connectors are still the standard input connector on active loudspeaker cabinets. To help users avoid overpowering them, loudspeakers have a power rating (in
watt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James ...
s) which indicates their maximum power capacity. Thanks to the efforts of the
Audio Engineering Society The Audio Engineering Society (AES) is a professional body for engineers, scientists, other individuals with an interest or involvement in the professional audio industry. The membership largely comprises engineers developing devices or product ...
(AES) and the loudspeaker industry group ALMA in developing the EIA-426 testing standard, power-handling specifications became more trustworthy. Lightweight, portable speaker systems for small venues route the low-frequency parts of the music (electric bass, bass drum, etc.) to a powered
subwoofer A subwoofer (or sub) is a loudspeaker designed to reproduce low-pitched audio frequencies known as bass and sub-bass, lower in frequency than those which can be (optimally) generated by a woofer. The typical frequency range for a subwoofer i ...
. Routing the low-frequency energy to a separate amplifier and subwoofer can substantially improve the bass response of the system. Also, clarity may be enhanced because low-frequency sounds can cause
intermodulation Intermodulation (IM) or intermodulation distortion (IMD) is the amplitude modulation of signals containing two or more different frequencies, caused by nonlinearities or time variance in a system. The intermodulation between frequency comp ...
and other distortion in speaker systems. Professional sound reinforcement speaker systems often include dedicated hardware for safely ''flying'' them above the stage area, to provide more even sound coverage and to maximize sightlines within performance venues.


Monitor loudspeakers

Monitor loudspeakers, also called ''foldback'' loudspeakers, are speaker cabinets used onstage to help performers to hear their singing or playing. As such, monitor speakers are pointed towards a performer or a section of the stage. They are generally sent a different mix of vocals or instruments than the mix that is sent to the main loudspeaker system. Monitor loudspeaker cabinets are often a wedge shape, directing their output upwards towards the performer when set on the floor of the stage. Simple two-way, dual-driver designs with a
speaker cone In the field of acoustics, a diaphragm is a transducer intended to inter-convert mechanical vibrations to sounds, or vice versa. It is commonly constructed of a thin membrane or sheet of various materials, suspended at its edges. The varying air ...
and a horn are common, as monitor loudspeakers need to be smaller to save space on the stage. These loudspeakers typically require less power and volume than the main loudspeaker system, as they only need to provide sound for a few people who are in relatively close proximity to the loudspeaker. Some manufacturers have designed loudspeakers for use either as a component of a small PA system or as a monitor loudspeaker. A number of manufacturers produce powered monitor speakers, which contain an integrated amplifier. Using monitor speakers instead of in-ear monitors typically results in an increase of stage volume, which can lead to more feedback issues and progressive hearing damage for the performers in front of them. The clarity of the mix for the performer on stage is also typically compromised as they hear more extraneous noise from around them. The use of monitor loudspeakers, active (with an integrated amplifier) or passive, requires more cabling and gear on stage, resulting in a more cluttered stage. These factors, amongst others, have led to the increasing popularity of in-ear monitors.


In-ear monitors

In-ear monitor In-ear monitors (IEMs) are devices used by musicians, audio engineers and audiophiles to listen to music or to hear a personal mix of vocals and stage instrumentation for live performance or recording studio mixing. They are also used by telev ...
s are headphones that have been designed for use as monitors by a live performer. They are either of a ''universal fit'' or ''custom fit'' design. The universal fit in-ear monitors feature rubber or foam tips that can be inserted into virtually anybody's ear. Custom-fit in-ear monitors are created from an impression of the user's ear that has been made by an
audiologist Audiology (from Latin , "to hear"; and from Greek , ''-logia'') is a branch of science that studies hearing, balance, and related disorders. Audiologists treat those with hearing loss and proactively prevent related damage. By employing vario ...
. In-ear monitors are almost always used in conjunction with a wireless transmitting system, allowing the performer to freely move about the stage while receiving their monitor mix. In-ear monitors offer considerable isolation for the performer using them, no on-stage sound is heard and the monitor engineer can deliver a much more accurate and clear mix for the performer. With in-ear monitors, each performer can be sent their own customized mix; although this was also the case with monitor speakers, the in-ear monitors of one performer cannot be heard by the other musicians. A downside of this isolation is that the performer cannot hear the crowd or the comments from other performers on stage that do not have microphones (e.g., if the bass player wishes to communicate to the drummer). This has been remedied in larger productions by setting up microphones facing the audience that can be mixed into the in-ear monitor sends. Since their introduction in the mid-1980s, in-ear monitors have grown to be the most popular monitoring choice for large touring acts. The reduction or elimination of loudspeakers other than instrument amplifiers on stage has allowed for cleaner and less problematic mixing for both the front of house and monitor engineers. [Audio feedback is greatly reduced and there is less sound reflecting off the back wall of the stage out into vocal mics and the audience, which improves the clarity of the front-of-house mix.


Applications

Sound reinforcement systems are used in a broad range of different settings, each of which poses different challenges.


Rental systems

Audio-visual rental systems have to be able to withstand heavy use and even abuse from renters. For this reason, rental companies tend to own speaker cabinets that are heavily braced and protected with steel corners, and electronic equipment such as power amplifiers or effects are often mounted into protective road cases. Rental companies also tend to select gear that have electronic protection features, such as speaker-protection circuitry and amplifier limiters. Rental systems for non-professionals need to be easy to use and set up and they must be easy to repair and maintain for the renting company. From this perspective, speaker cabinets need to have easy-to-access horns, speakers, and crossover circuitry, so that repairs or replacements can be made. Many touring acts and large venue corporate events will rent large sound reinforcement systems that typically include one or more audio engineers on staff with the renting company. In the case of rental systems for tours, there are typically several audio engineers and technicians from the rental company that tour with the band to set up and calibrate the equipment. The individual that mixes the band is often selected and provided by the band, as they are familiar with the various aspects of the show and understand how the band wants the show to sound.


Live music clubs and dance events

Setting up sound reinforcement for live music clubs and dance events often poses unique challenges, because there is such a large variety of venues that are used as clubs, ranging from former warehouses or music theaters to small restaurants or basement pubs with concrete walls. Dance events may be held in huge warehouses, aircraft hangars or outdoor spaces. In some cases, clubs are housed in multi-story venues with balconies or in L-shaped rooms, which makes it hard to get a consistent sound for all audience members. The solution is to use fill-in speakers to obtain good coverage, using a delay to ensure that the audience does not hear the same reinforced sound at different times. The number of
subwoofer A subwoofer (or sub) is a loudspeaker designed to reproduce low-pitched audio frequencies known as bass and sub-bass, lower in frequency than those which can be (optimally) generated by a woofer. The typical frequency range for a subwoofer i ...
speaker cabinets and power amplifiers dedicated to low-frequency sounds used in a club depends on the type of club, the genres of music played there, and the size of the venue. A small
coffeehouse A coffeehouse, coffee shop, or café is an establishment that primarily serves coffee of various types, notably espresso, latte, and cappuccino. Some coffeehouses may serve cold drinks, such as iced coffee and iced tea, as well as other non-ca ...
where traditional folk, bluegrass or jazz groups are the main performers may have no subwoofers, and instead rely on the full-range main PA speakers to reproduce bass sounds. On the other hand, a club where
hard rock Hard rock or heavy rock is a loosely defined subgenre of rock music typified by aggressive vocals and distorted electric guitars. Hard rock began in the mid-1960s with the garage, psychedelic and blues rock movements. Some of the earliest ha ...
or
heavy metal music Heavy metal (or simply metal) is a genre of rock music that developed in the late 1960s and early 1970s, largely in the United Kingdom and United States. With roots in blues rock, psychedelic rock and acid rock, heavy metal bands develope ...
bands play or a
nightclub A nightclub (music club, discothèque, disco club, or simply club) is an entertainment venue during nighttime comprising a dance floor, lightshow, and a stage for live music or a disc jockey (DJ) who plays recorded music. Nightclubs gen ...
where DJs play
dance music Dance music is music composed specifically to facilitate or accompany dancing. It can be either a whole musical piece or part of a larger musical arrangement. In terms of performance, the major categories are live dance music and recorded da ...
may have multiple large subwoofers, as these genres and music styles typically use powerful, deep bass sound. A challenge with designing sound systems for clubs is that the sound system may need to be used for both prerecorded music played by DJs and live music. A club system designed for DJs needs a
DJ mixer A DJ mixer is a type of audio mixing console used by disc jockeys (DJs) to control and manipulate multiple audio signals. Some DJs use the mixer to make seamless transitions from one song to another when they are playing records at a dance clu ...
and space for
record player A phonograph, in its later forms also called a gramophone (as a trademark since 1887, as a generic name in the UK since 1910) or since the 1940s called a record player, or more recently a turntable, is a device for the mechanical and analogu ...
s. In contrast, a live music club needs a mixing board designed for live sound, an onstage monitor system, and a multicore snake cable running from the stage to the mixer. Clubs that feature both types of shows may face challenges providing the desired equipment and set-up for both uses. Clubs can be a hostile environment for sound gear, in that the air may be hot, humid, and smoky. In some clubs, keeping power amplifiers cool may be a challenge.


Church sound

Churches and similar houses of worship often pose design challenges. Speakers may need to be unobtrusive to blend in with antique woodwork and stonework. In some cases, audio designers have designed custom-painted speaker cabinets. Some facilities, such as sanctuaries or chapels are long rooms with low ceilings and additional fill-in speakers are needed throughout the room to give good coverage. Once installed, church systems are often operated by amateur volunteers from the congregation, which means that they must be easy to operate and troubleshoot. To this end, some mixing consoles designed for houses of worship have automatic mixers, which turn down unused channels to reduce noise, and automatic feedback elimination circuits which detect and notch out frequencies that are feeding back. These features may also be available in multi-function consoles used in convention facilities and multi-purpose venues.


Touring systems

Touring sound systems are available in many different sizes and shapes as they have to be powerful and versatile enough to cover many different halls and venues. Touring systems range from mid-sized systems for bands playing
nightclub A nightclub (music club, discothèque, disco club, or simply club) is an entertainment venue during nighttime comprising a dance floor, lightshow, and a stage for live music or a disc jockey (DJ) who plays recorded music. Nightclubs gen ...
and other mid-sized venues to large systems for groups playing
stadium A stadium ( : stadiums or stadia) is a place or venue for (mostly) outdoor sports, concerts, or other events and consists of a field or stage either partly or completely surrounded by a tiered structure designed to allow spectators to stand o ...
s, arenas and
outdoor festival A music festival is a community event with performances of singing and instrument playing that is often presented with a theme such as musical genre (e.g., rock, blues, folk, jazz, classical music), nationality, locality of musicians, or hol ...
s. Tour sound systems are often designed with substantial redundancy features, so that in the event of equipment failure or amplifier overheating, the system will continue to function. Touring systems for bands performing for crowds of a few thousand people and up are typically set up and operated by a team of technicians and engineers who travel with the performers to every show. Mainstream bands that are going to perform in mid- to large-sized venues during their tour schedule one to two weeks of technical rehearsal with the entire concert system and production staff, including audio engineers, at hand. This allows the audio and lighting engineers to become familiar with the show and establish presets on their digital equipment (e.g., digital mixers) for each part of the show, if needed. Many modern musical groups work with their
front of house In the performing arts, front of house (FOH) is the part of a performance venue that is open to the public. In theatres and live music venues, it consists of the auditorium and foyers, as opposed to the stage and backstage areas. In a theatre, ...
and monitor mixing engineers during this time to establish what their general idea is of how the show and mix should sound, both for themselves on stage and for the audience. This often involves programming different effects and signal processing for use on specific songs, to make the songs sound somewhat similar to the studio versions. To manage a show with a lot of effects changes, the mixing engineers for the show often choose to use a
digital mixing console In professional audio, a digital mixing console (DMC) is a type of mixing console used to combine, route, and change the dynamics, equalization and other properties of multiple audio input signals, using digital signal processing rather than a ...
so that they can save and automatically recall these many settings in between each song. This time is also used by the system technicians to get familiar with the specific combination of gear that is going to be used on the tour and how it acoustically responds during the show. These technicians remain busy during the show, making sure the SR system is operating properly and that the system is tuned correctly, as the acoustic response of a room or venue will respond differently throughout the day depending on the temperature, humidity, and number of people in the room or space.


Live theater

Sound for live theater, operatic theater, and other dramatic applications may pose problems similar to those of churches; theaters may be in heritage buildings where speakers and wiring is required to blend in with the architecture. The need for clear
sightlines In architecture, sightlines are a particularly important consideration in the design of civic structures, such as a stage, arena, or monument. They determine the configuration of such items as theater and stadium design, road junction layout an ...
may make the use of regular speaker cabinets unacceptable; instead, slim, low-profile speakers are often used instead. In live theater and drama, performers move around onstage, which means that
wireless microphone A wireless microphone, or cordless microphone, is a microphone without a physical cable connecting it directly to the sound recording or amplifying equipment with which it is associated. Also known as a radio microphone, it has a small, battery ...
s may be necessary. Some of the higher-budget theater shows and musicals are mixed in surround sound live, often with the show's sound operator triggering sound effects that are being mixed with music and dialogue by the show's mixing engineer. These systems are usually much more extensive to design, typically involving separate sets of speakers for different zones in the theater.


Classical music and opera

A subtle type of sound reinforcement called
acoustic enhancement Acoustic enhancement is a subtle type of sound reinforcement system used to augment direct, reflected, or reverberant sound. While sound reinforcement systems are usually used to increase the sound level of the sound source (like a person speaking ...
is used in some concert halls where classical music such as symphonies and opera is performed. Acoustic enhancement systems add more sound to the hall and prevent ''dead spots'' in the audience seating area by "...augment nga hall's intrinsic acoustic characteristics." The systems use "...an array of microphones connected to a computer
hich is Ij ( fa, ايج, also Romanized as Īj; also known as Hich and Īch) is a village in Golabar Rural District, in the Central District of Ijrud County, Zanjan Province, Iran Iran, officially the Islamic Republic of Iran, and also ...
connected to an array of loudspeakers." However, as concertgoers have become aware of the use of these systems, debates have arisen, because "...purists maintain that the natural acoustic sound of lassicalvoices rinstruments in a given hall should not be altered." Kai Harada's article ''Opera's Dirty Little Secret'' states that opera houses have begun using electronic acoustic enhancement systems "...to compensate for flaws in a venue's acoustical architecture." Despite the uproar that has arisen amongst operagoers, Harada points out that none of the opera houses using acoustic enhancement systems "...use traditional, Broadway-style sound reinforcement, in which most if not all singers are equipped with radio microphones mixed to a series of unsightly loudspeakers scattered throughout the theatre." Instead, most opera houses use the sound reinforcement system for acoustic enhancement, and for subtle boosting of offstage voices, onstage dialogue, and sound effects (e.g., church bells in
Tosca ''Tosca'' is an opera in three acts by Giacomo Puccini to an Italian libretto by Luigi Illica and Giuseppe Giacosa. It premiered at the Teatro Costanzi in Rome on 14 January 1900. The work, based on Victorien Sardou's 1887 French-language dramati ...
or thunder in Wagnerian operas). These systems use microphones, computer processing "with delay, phase, and frequency-response changes", and then send the signal "... to a large number of loudspeakers placed in extremities of the performance venue." Another acoustic enhancement system, VRAS uses "...different algorithms based on microphones placed around the room." The Deutsche Staatsoper in Berlin and the Hummingbird Centre in Toronto use a
LARES Lares ( , ; archaic , singular ''Lar'') were guardian deities in ancient Roman religion. Their origin is uncertain; they may have been hero-ancestors, guardians of the hearth, fields, boundaries, or fruitfulness, or an amalgam of these. Lare ...
system. The Ahmanson Theatre in Los Angeles, the Royal National Theatre in London, and the
Vivian Beaumont Theater The Vivian Beaumont Theater is a Broadway theater in the Lincoln Center complex at 150 West 65th Street on the Upper West Side of Manhattan in New York City. Operated by the nonprofit Lincoln Center Theater (LCT), the Beaumont is the only Bro ...
in New York City use the SIAP system.


Lecture halls and conference rooms

Lecture halls and conference rooms pose the challenge of reproducing speech clearly to a large hall, which may have reflective,
echo In audio signal processing and acoustics, an echo is a reflection of sound that arrives at the listener with a delay after the direct sound. The delay is directly proportional to the distance of the reflecting surface from the source and the lis ...
-producing surfaces. One issue with reproducing speech is that the microphone used to pick up the sound of an individual's voice may also pick up unwanted sounds, such as the rustling of papers on a podium. A more tightly directional microphone may help to reduce unwanted background noises. Another challenge with doing live sound for individuals who are speaking at a conference is that, in comparison with professional singers, individuals who are invited to speak at a forum may not be familiar with how microphones work. Some individuals may accidentally point the microphone towards a speaker or monitor speaker, which may cause
audio feedback Audio feedback (also known as acoustic feedback, simply as feedback) is a positive feedback situation which may occur when an acoustic path exists between an audio input (for example, a microphone or guitar pickup) and an audio output (for exa ...
"howls". In some cases, when an individual who is speaking does not speak enough directly into the microphone, the audio engineer may ask the individual to wear a lavaliere microphone, which can be clipped onto a lapel. In some conferences, sound engineers have to provide microphones for a large number of people who are speaking, in the case of a panel conference or debate. In some cases, automatic mixers are used to control the levels of the microphones, and turn off the channels for microphones that are not being spoken into, to reduce unwanted background noise and reduce the likelihood of feedback.


Sports sound systems

Systems for outdoor sports facilities and ice rinks often have to deal with substantial echo, which can make speech unintelligible. Sports and recreational sound systems often face environmental challenges as well, such as the need for weather-proof outdoor speakers in outdoor stadiums and
humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity dep ...
- and splash-resistant speakers in swimming pools. Another challenge with sports sound reinforcement setups is that in many arenas and stadiums, the spectators are on all four sides of the playing field. This requires 360-degree sound coverage. This is very different from the norm with music festivals and music halls, where the musicians are on stage and the audience is seated in front of the stage.


Setting up and testing

Large-scale sound reinforcement systems are designed, installed, and operated by audio engineers and audio technicians. During the design phase of a newly constructed venue, audio engineers work with architects and contractors, to ensure that the proposed design will accommodate the speakers and provide an appropriate space for sound technicians and the racks of audio equipment. Sound engineers will also provide advice on which audio components would best suit the space and its intended use, and on the correct placement and installation of these components. During the installation phase, sound engineers ensure that high-power electrical components are safely installed and connected and that ceiling or wall-mounted speakers are properly mounted (or "flown") onto
rigging Rigging comprises the system of ropes, cables and chains, which support a sailing ship or sail boat's masts—''standing rigging'', including shrouds and stays—and which adjust the position of the vessel's sails and spars to which they ar ...
. When the sound reinforcement components are installed, the sound engineers test and calibrate the system so that its sound production will be even across the frequency spectrum.


System testing

A sound reinforcement system should be able to accurately reproduce a signal from its input, through any processing, to its output without any coloration or distortion. However, due to inconsistencies in venue sizes, shapes, building materials, and even crowd densities, this is not always possible without prior calibration of the system. This can be done in one of several ways. The oldest method of system
calibration In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of kno ...
involves a set of healthy ears, test program material (i.e. music or speech), a graphic equalizer, and last but certainly not least, a familiarity with the proper (or desired) frequency response. One must then listen to the program material through the system, take note of any noticeable frequency changes or resonances, and subtly correct them using the equalizer. Experienced engineers typically use a specific playlist of music that they have become very familiar with every time they calibrate a new system. This "by ear" process is still done by many engineers, even when analysis equipment is used, as a final check of how the system sounds with music or speech playing through the system. Another method of manual calibration requires a pair of high-quality headphones patched into the input signal ''before'' any processing (such as the pre-fade-listen of the test program input channel of the mixing console, or the headphone output of the CD player or tape deck). One can then use this direct signal as a near-perfect reference with which to find any differences in frequency response. This method may not be perfect, but it can be very helpful with limited resources or time, such as using pre-show music to correct for the changes in response caused by the arrival of a crowd. Because this is still a very subjective method of calibration, and because the human ear is so dynamic in its own response, the program material used for testing should be as similar as possible to that for which the system is being used. Since the development of
digital signal processing Digital signal processing (DSP) is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The digital signals processed in this manner are ...
(DSP), there have been many pieces of equipment and computer software designed to shift the bulk of the work of system calibration from human auditory interpretation to software algorithms that run on microprocessors. One tool for calibrating a sound system using either DSP or Analog Signal Processing is a
Real Time Analyzer A real-time analyzer (RTA) is a professional audio device that measures and displays the frequency spectrum of an audio signal; a spectrum analyzer that works in real time. An RTA can range from a small PDA-sized device to a rack-mounted hard ...
(RTA). This tool is usually used by piping
pink noise Pink noise or noise is a signal or process with a frequency spectrum such that the power spectral density (power per frequency interval) is inversely proportional to the frequency of the signal. In pink noise, each octave interval (halving ...
into the system and measuring the result with a special calibrated microphone connected to the RTA. Using this information, the system can be adjusted to help achieve the desired response. The displayed response from the RTA mic cannot be taken as a perfect representation of the room as the analysis will be different, sometimes drastically, when the mic is placed in different position in front of the system. More recently, sound engineers have seen the introduction of dual fast-Fourier transform (FFT) based audio analysis software which allows an engineer to view not only frequency vs. amplitude (pitch vs. volume) information that an RTA provides, but also to see the same signals (sounds) in the time domain. This provides the engineer with much more meaningful data than an RTA alone. Also, dual FFT analysis allows one to compare the source signal with the output signal and view the difference. This is a very fast way to calibrate a system to sound as close as possible to the original source material. As with any such measurement tool, it must always be verified using actual human ears. Some DSP system processing devices have been designed for use by non-professionals that automatically make adjustments in the system EQ based upon what is being read from the RTA mic. These are practically never used by professionals, as they almost never calibrate the system as well as a professional audio engineer can manually.


Equipment supply stores

Professional audio store A professional audio store is a retail business that sells, and in many cases rents, sound reinforcement system equipment and PA system components used in music concerts, live shows, dance parties and speaking events. This equipment typically inc ...
s sell microphones,
speaker enclosure A loudspeaker enclosure or loudspeaker cabinet is an enclosure (often rectangular box-shaped) in which speaker drivers (e.g., loudspeakers and tweeters) and associated electronic hardware, such as crossover circuits and, in some cases, power ...
s,
monitor Monitor or monitor may refer to: Places * Monitor, Alberta * Monitor, Indiana, town in the United States * Monitor, Kentucky * Monitor, Oregon, unincorporated community in the United States * Monitor, Washington * Monitor, Logan County, West ...
speakers,
mixing board A mixing console or mixing desk is an electronic device for mixing audio signals, used in sound recording and reproduction and sound reinforcement systems. Inputs to the console include microphones, signals from electric or electronic in ...
s, rack-mounted
effects unit An effects unit or effects pedal is an electronic device that alters the sound of a musical instrument or other audio source through audio signal processing. Common effects include distortion/overdrive, often used with electric guitar in ...
s and related equipment designed for use by audio engineers and technicians. Professional audio stores are also called "pro audio stores", "pro sound stores", "sound reinforcement" companies, "PA system companies" or "audio-visual companies", with the latter name being used when a store supplies a significant amount of video equipment for events, such as video projectors and screens. Stores often use the word "professional" or "pro" in their name or the description of their store, to differentiate their stores from consumer
electronics store A consumer electronics store, in the United States and some other countries, is a physical store that sells consumer electronics. As technology has progressed, the United States has known variations such as phonograph dealers, radio stores, hi-f ...
s, which sell consumer-grade
loudspeaker A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A ''speaker system'', also often simply referred to as a "speaker" or ...
s,
home cinema Home cinema, also called home theaters or theater rooms, are home entertainment audio-visual systems that seek to reproduce a movie theater experience and mood using consumer electronics-grade video and audio equipment that is set up in a room ...
equipment, and amplifiers, which are designed for private, in-home use.


Notes


References

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Further reading


Books

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Papers

* Benson, J.E. "Theory and Design of Loudspeaker Enclosures", ''Amalgamated Wireless Australia Technical Review'', (1968, 1971, 1972). * Beranek, L., "Loudspeakers and Microphones", ''J. Acoustical Society of America'', volume 26, number 5 (1954). * Damaske, P., "Subjective Investigation of Sound Fields", ''Acustica'', Vol. 19, pp. 198–213 (1967–1968). * Davis, D & Wickersham, R., "Experiments in the Enhancement of the Artist's Ability to Control His Interface with the Acoustic Environment in Large Halls", presented at the 51st AES Convention, 13–16 May 1975; preprint number 1033. * Eargle J. & Gelow, W., "Performance of Horn Systems: Low-Frequency Cut-off, Pattern Control, and Distortion Trade-offs", presented at the 101st Audio Engineering Society Convention, Los Angeles, 8–11 November 1996. Preprint number 4330. * Engebretson, M., "Low Frequency Sound Reproduction", ''J. Audio Engineering Society'', volume 32, number 5, pp. 340–352 (May 1984) * French, N. & Steinberg, J., "Factors Governing the Intelligibility of Speech Sounds", ''J. Acoustical Society of America'', volume 19 (1947). * Gander, M. & Eargle, J., "Measurement and Estimation of Large Loudspeaker Array Performance", ''J. Audio Engineering Society'', volume 38, number 4 (1990). * Henricksen, C. & Ureda, M., "The Manta-Ray Horns", ''J. Audio Engineering Society'', volume 26, number, pp. 629–634 (September 1978). * Hilliard, J., "Historical Review of Horns Used for Audience-Type Sound Reproduction", ''J. Acoustical Society of America'', volume 59, number 1, pp. 1 – 8, (January 1976) * Houtgast, T. and Steeneken, H., "Envelope Spectrum Intelligibility of Speech in Enclosures", presented at IEEAFCRL Speech Conference, 1972. * Klipsch, P. "Modulation Distortion in Loudspeakers: Parts 1, 2, and 3" ''J. Audio Engineering Society'', volume 17, number 2 (April 1969), volume 18, number 1 (February 1970), and volume 20, number 10 (December 1972). * Lochner, P. & Burger, J., "The Influence of Reflections on Auditorium Acoustics", ''Sound and Vibration'', volume 4, pp. 426–54 (196). * Meyer, D., "Digital Control of Loudspeaker Array Directivity", ''J. Audio Engineering Society'', volume 32, number 10 (1984). * Peutz, V., "Articulation Loss of Consonants as a Criterion for Speech Transmission in a Room", ''J. Audio Engineering Society'', volume 19, number 11 (1971). * Rathe, E., "Note on Two Common Problems of Sound Reproduction", ''J. Sound and Vibration'', volume 10, pp. 472–479 (1969). * Schroeder, M., "Progress in Architectural Acoustics and Artificial Reverberation", ''J. Audio Engineering Society'', volume 32, number 4, p. 194 (1984) * Smith, D., Keele, D., and Eargle, J., "Improvements in Monitor Loudspeaker Design", ''J. Audio Engineering Society'', volume 31, number 6, pp. 408–422 (June 1983). * Toole, F., "Loudspeaker Measurements and Their Relationship to Listener Preferences, Parts 1 and 2", ''J. Audio Engineering Society'', volume 34, numbers 4 & 5 (1986). * Veneklasen, P., "Design Considerations from the Viewpoint of the Consultant", ''Auditorium Acoustics'', pp. 21–24, Applied Science Publishers, London (1975). * Wente, E. & Thuras, A., "Auditory Perspective — Loudspeakers and Microphones", ''Electrical Engineering'', volume 53, pp. 17–24 (January 1934). Also, BSTJ, volume XIII, number 2, p. 259 (April 1934) and Journal AES, volume 26, number 3 (March 1978). {{div col end Sound production technology Technology systems Audio amplifiers Audio engineering Loudspeakers Audio mixing