Editing Sound reinforcement system (section)

==System components==

===Input transducers===
[[File:Various-microphones.JPG|thumb|right|200px|Audio engineers use a range of microphones for different live sound applications.]]
[[Image:Polar pattern cardioid.png|thumb|right|170px|[[Cardioid]] mics are widely used in live sound, because their "apple-shaped" pickup pattern rejects sounds from the sides and rear of the mic, making it more resistant to unwanted [[audio feedback|feedback]] "howls".]]

Many types of input [[transducer]]s can be found in a sound reinforcement system, with [[microphone]]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 microphone|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 (audio)|headset mounts]]. Microphones on stands are also placed in front of [[instrument amplifier]]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]],{{sfn |Eargle|Foreman|2002| p=62}} [[Kate Bush]], and [[Madonna]].<ref>{{cite news| last=Badhorn|first=Philippe|title=Interview in Rolling Stone (France)|publisher=[[Rolling Stone]] |date=February 2006 }}</ref>

Other types of input transducers include [[magnetic pickup]]s used in electric guitars and electric basses, [[contact microphone]]s used on stringed instruments, and pianos and [[phonograph]] pickups (cartridges) used in record players. Electronic instruments such as [[synthesizer]]s 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, [[Wireless microphone|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===
[[File:Two Consoles at FOH.jpg|thumb|left|300 px|A Yamaha PM4000 and a Midas Heritage 3000 mixing console at the front of house position at an outdoor concert.]]

[[Mixing console]]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]], 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]]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.<ref>{{citation |url=http://www.prosoundweb.com/install/tfw/eng/mon.php |archive-url=https://web.archive.org/web/20080325202949/http://www.prosoundweb.com/install/tfw/eng/mon.php |archive-date=2008-03-25 |title=The Monitor Engineer's Role in Performance |author=Philip Manor}}</ref>{{efn|In cases where performers have to play at a venue that does not have a monitor engineer near the stage, the monitor mixing is done by the FOH engineer from the FOH console. This arrangement can be problematic because the performers end up having to request changes to the monitor mixes with "...hand signals and clever cryptic phrases" which may be misunderstood. The engineer also cannot hear the changes that he is applying to the monitors on stage, often resulting in a reduction of the quality of the onstage monitor mix.<ref>{{citation |url=http://www.sweetwater.com/expert-center/techtips/d--02/16/2004 |title=Advantages of a Dedicated Monitor Mixing Console |date=2004-02-16 |access-date=2019-01-07 |publisher=[[Sweetwater Sound]]}}</ref>}}

===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 equalizer]]s, 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, [[Delay (audio effect)|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====
[[Image:Graphic equalizer.jpg|thumb|200px|Graphic equalizer]]
[[Equalization (audio)|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 equalizer]]s. Graphic equalizers have [[fade (audio engineering)|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 that are too weak, such as a singer with modest projection in their lower register, can be boosted. Frequencies that are too loud, such as a "boomy" sounding [[bass drum]], or an overly resonant [[dreadnought guitar]] can be cut. Sound reinforcement systems typically use graphic equalizers with one-third [[octave]] frequency centers. These are typically used to equalize output signals going to the main loudspeaker system or the monitor speakers on stage. [[Parametric equalization|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 that 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]] (high-cut) filter may also be included on equalizers or audio consoles. High-pass and low-pass filters restrict a given channel's [[Bandwidth (signal processing)|bandwidth]] 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 subwoofer drivers. A low-pass filter to cut [[ultrasonic]] 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]] filter, eliminating undesirable frequencies both above and below the auditory spectrum. A [[band-stop filter]], does the opposite. It allows all frequencies to pass except for one band in the middle. A feedback suppressor, using an [[embedded system|microprocessor]], automatically detects the onset of feedback and applies a narrow band-stop filter (a [[notch filter]]) at specific frequency or frequencies pertaining to the feedback.

====Compressors====
[[File:Comp. rack (Supernatural).jpg|thumb|150px|A rack of electronic audio compressors]]
[[Dynamic range compression]] 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]]. The speed that the compressor adjusts the gain of the signal ([[Envelope (music)|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.

[[File:FOH Racks.jpg|thumb|right|250px|Effect processing rack-mounted units at the FOH position at an outdoor concert.]]

====Noise gates====
A [[noise gate]] 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]] and [[Delay (audio effect)|delay]] 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).<ref>[http://www.harmony-central.com/Effects/Articles/Reverb/ Reverberation]. Harmony-Central. Retrieved on January 23, 2009.</ref>  Many modern mixing boards designed for live sound include on-board reverb effects.

Other effects include modulation effects such as [[Flanger]], [[Phaser (effect)|phaser]], and [[chorus effect|chorus]] and spectral manipulation or harmonic effects such as the [[Exciter (effect)|exciter]] and [[harmonizer]]. 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]] 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]], [[music producer]], or musical director.

====Feedback suppressor====
A [[feedback suppressor]] detects unwanted [[audio feedback]] and suppresses it, typically by automatically inserting a [[notch filter]] 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]]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===
[[Image:Poweramps.JPG|thumb|200px|Three audio power amplifiers]]
[[Image:Connectors of a QSC PLX2402 professional PA Power Amplifier.jpg|thumb|Rear panel of a power amplifier with 2 × 700 Watt (4 Ohm) - very similar to the topmost device in the image above - showing typical connectors for professional use: From left, symmetrical [[XLR connector|XLR]]-sockets for signal input, alternatively [[audio jack]] sockets, loudspeaker terminals of type [[Speakon]] (center), alternatively conventional [[screw terminal]]s for the loudspeaker cables (black and red per channel).]]

A [[power amplifier]] is an electronic device that uses electrical power and circuitry to boost a [[line level]] signal and provides enough electrical power to drive a loudspeaker and produce sound. All loudspeakers, including [[headphones]], require power amplification. Most professional audio power amplifiers also provide protection from [[clipping (audio)|clipping]] typically as some form of [[limiting]]. A power amplifier pushed into clipping can damage loudspeakers. Amplifiers also typically provide protection against [[short circuit]]s across the output and overheating.

Audio engineers select amplifiers that provide enough [[Headroom (audio signal processing)|headroom]]. Headroom refers to the amount by which the signal-handling capabilities of an audio system exceed a designated [[nominal level]].<ref>{{cite web |url=http://www.soundonsound.com/sound-advice/q-what-exactly-headroom-and-why-it-important |title=Q. What exactly is 'headroom' and why is it important? |date=February 2010 |publisher=[[Sound on Sound]]}}</ref> 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 (audio)|clipping]]. 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]]s. Rack-mounted amps are typically housed in [[road case]]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.<ref name="vasey1999concert">{{cite book |title=Concert Sound and Lighting Systems |last=Vasey |first=John |isbn=9780240803647 |lccn=lc99030654 |url=https://books.google.com/books?id=emthlAnw7l4C |date=1999 |publisher=Focal Press |chapter=5, Power amplifiers}}</ref>  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]]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]] and [[class D amplifier]]s, 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]] 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]] circuits.

===Main loudspeakers===
[[File:Line Array and Subs.jpg|thumb|left|250px|A large line array with separate subs and a smaller side fill line array.]]
A simple and inexpensive PA [[loudspeaker]] may have a single full-range [[loudspeaker driver]], housed in a suitable enclosure. More elaborate, professional-caliber sound reinforcement loudspeakers may incorporate separate drivers to produce low, middle, and high [[frequency]] sounds. A [[crossover network]] routes the different frequencies to the appropriate drivers. In the 1960s, [[Horn loudspeaker|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 [[Compression driver|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 array]]s, where long vertical arrays of loudspeakers in smaller cabinets are used to increase efficiency and provide even dispersion and frequency response. [[Trapezoidal]]-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]] 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]]s, specialized current-limiting light bulbs, and [[circuit breaker]]s were used alone or in combination to reduce driver failures. During the same period, the professional sound reinforcement industry made the Neutrik [[Speakon]] NL4 and NL8 connectors the standard speaker connectors, replacing [[1/4" jack]]s, [[XLR connector]]s, and [[Cannon (ITT Corporation)|Cannon]] 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]]s) which indicates their maximum power capacity. Thanks to the efforts of the [[Audio Engineering Society]] (AES) and the loudspeaker industry group ALMA in developing the EIA-426 testing standard, power-handling specifications became more trustworthy.

[[File:Mackie SWA1801 subwoofer.jpg|thumb|right|200px|An 18" Mackie [[subwoofer]] cabinet.]]
Lightweight, portable speaker systems for small venues route the low-frequency parts of the music (electric bass, bass drum, etc.) to a powered [[subwoofer]]. 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]] 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===
[[Image:12andbullet.jpg|thumb|A JBL floor monitor speaker cabinet with a {{convert|12|in|cm|abbr=on}} woofer and a "bullet" tweeter. Most monitor cabinets have a metal grille or woven plastic mesh to protect the loudspeaker.]]
[[Foldback (sound engineering)|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 [[Dynamic loudspeaker|speaker cone]] 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 speakers|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.<ref name="in-ear tips">{{cite web|url=http://www.audiologyonline.com/articles/article_detail.asp?article_id=2115|title=In-Ear Monitors: Tips of the Trade|access-date=2009-01-24}}</ref>  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===
[[Image:InEarMonitors.jpg|thumb|right|200 px|A pair of universal fit [[in-ear monitor]]s. This particular model is the Etymotic ER-4S]]
[[In-ear monitor]]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]]. 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.<ref name="in-ear tips" />

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.