Public address system

The PA system (including public address, PA called short ) is a sound system, which serves the reproduction and reinforcement of speech or music. It consists of speakers and amplifiers. Often the controlling mixer and the associated effects units of the PA be attributed.

PA systems are used wherever it is necessary to sonicate large areas as evenly as possible.

The PA system is a branch of stage equipment and sound engineering.

The job of a PA system is to transmit voice or music information to an audience.

In German, the term " PA " focused primarily on the stage technique relates (English: Sound Reinforcement System). Facilities for the transmission of pure linguistic information such as Local call systems are summarized under the term electro-acoustic system, which is of English origin meaning ( " public address " ) closer.

Since speakers of the frequency to be transmitted have different emission characteristics dependent and sound is refracted differently depending on the frequency, PA systems are often divided into bass speaker and agent / tweeter. In addition, usually, it is possible not to add a subwoofer.

Because of the high cost of transportation and construction, the PA is often provided by the organizers, especially for small to medium-sized gigs or festivals, (or several days) can take care of in advance to build up at the venue unless it anyway a stationary PA system holds (eg in discotheques ). Sizing and design of the PA are then adapted to the requirements of the venue. For larger shows and on longer tours the PA on the other hand usually transported from venue to venue. In some cases, even multiple identical systems are used so that an ever closest venue parallel can be established already.

On the PA system includes the so-called backline that will bring added from the performing artists themselves and is tailored to their individual needs. In contrast to the PA the backline between the successive appearances of several performer has chosen can be easily replaced.

Use of PA speakers

Small PA systems that are used as for birthdays, weddings, lectures, bands and other musical purposes, it is mostly made ​​up of one or two subwoofers and two to four mid-high speakers. Large PA systems who come to concerts, theater performances or in discos and events tent to use, provide mostly composed of at least four subwoofers and six mid-high speakers. The number of speakers is in principle open so that on large concerts often 40 or more speakers are used. On stage the speakers are often connected to each other and towers with additional flying on truss suspended ( " flown" ).

For larger events, one often takes the bass range six 18 " woofers ( each with 1 kW), also two double 21" woofers which provide the deep bass.

Meanwhile, there has, however, enforced to use at major events so-called line arrays, since these systems due to the differences in performance in spherical and cylindrical waves in general, better results can be achieved. The two speaker arrays to the stage sides are called the left and right PA Wing (English wing).


In addition to the PA there are at musical events usually also a monitor system that allows the artists on stage, better to hear their own voices and instruments as the sound direction of the PA is usually away from the stage and therefore on the stage only a dull sound or time- delayed reflections of the hall back wall or remote buildings can be heard without monitoring. At a distance of reflection walls of 50 meters, the sound waves for round trip need already almost 1 /3 second.

Monitor systems are especially needed in the live music, mainly because the drums makes a singer without its own sound it almost impossible to make sounds correctly if this can not hear themselves. By stage speaker, the performer received a similar listening experience as the audience and can coordinate the interaction better.

The monitoring can be implemented by looking on the stage speakers or through earphones ( in-ear monitoring). The latter is used more frequently with increasing development to reduce costs in the wireless technology, there can thus reduce feedback problems significantly.

Also the sound toward listeners may benefit from the in-ear monitoring, as the sound can be on the stage much quieter and not as strongly mixed with the PA sound to the audience addressed. This can have a much clearer sound result, especially in reverberant and small spaces.

Operation of a PA system

Such large systems can not be operated with a standard amplifier of the private client area, as PA systems often need to apply a power of several kilowatts and in addition to special requirements in terms of reliability. For this purpose, several stages are used with very high performance typically that drive most of the individual channels (mostly right / left, but also additional channels such as a delay line ) and frequency ranges ( Tief-/Mittel-/Hochtonbereich ) separately. With active speakers, the amplifiers are built directly into the speakers.

The complete PA sound system is controlled via a mixing console that is connected to the output stages. The mixer is the preamp and has next to microphone and instrument inputs usually also connections for eg CD player or other music players and connections for effects pedals, control amplifier and equalizer, all of which have the task of music and language to change so that the desired sound is achieved. Most of these devices are made in 19-inch units in the appropriate racks (eg Siderack ) can then be screwed.

Wiring of a PA system

The signal path starts on the one hand on the stage at the instruments and provided microphones: Here, mostly with XLR cables, the various signals in a stage box and in a to the mixer leading multicore or - for smaller systems - directly via XLR cable into the mixer routed. The XLR cables are connected symmetrically in the rule so that cancel out any irradiations each other. In addition to the stage signals, the above -mentioned signal sources ( CD recordings, etc.) connected to the mixer (some with RCA cables); Control amplifier are usually looped over insert cable (stereo plug to dual mono jack ) into the signal path.

The signal mixed to arrive at the final stages (by Multicore / XLR), which (due to the ohmic resistance of the cables) are ideally located near the speaker or incorporated into it. These are, EP5, formerly often XLR cable connected via the loudspeaker Speakon (which must be different but connected as XLR microphone cable ) with the final stages. The connections between power amplifiers and loudspeakers special jacks are often ( no matter which plug-in system ) is used, the plug is inserted in close contact, without the operation of the output stage is inhibited. In this way, damage to the output stage can be avoided by self-induction of an open output transformer.

Modern sound systems transmit digital audio over a network (LAN, WAN), whereby, for example, the language of digitized directly at the station and converted back to analog signals just before the amplifier. Between cycles the data as a digital signal processor (DSP) or parametric equalizer.


Special attention is paid to the live sound on the feedback of freedom of the system.

Since they often move to another place and must produce high sound pressure, sound systems are designed differently than hi- fi systems. PA systems are more robust and more difficult, since even at high volume, the speaker enclosure may not resonate. For major events are used for assembly and dismantling and loading (often accompanying ) workers, so-called roadies used. In addition, PA systems are much more complicated to set as hi-fi systems. Therefore, responsible for the wiring and the sound check one or more specially trained sound engineer.

To reduce momentary reflections and reverberation in a room, it is important to sonicate the only areas in which audience is located. For this purpose,

  • Duration Delayed support speaker

Employed. Important last point is the consideration of Haas effect, trading and duration and level difference.

  • (mostly vertically oriented ) loudspeaker arrays
  • (mostly horizontally oriented ) speaker cluster
  • Waveguides and Horn Loudspeaker

Furthermore, the maximum achievable sound levels are ( be so with greater efficiency, for example, Horn speaker, used for PA speakers), operational reliability, even under permanent overload, handling during assembly and disassembly (robustness, round corners) is crucial.

Although requirements differ from those at a hi-fi system, some PA systems achieve quite the playback quality of your hi-fi or studio systems (especially PA systems for operas, concert halls and movie theaters ). The overall sound of a PA system, however, is not negligible depending on the skill of the operator and the used measurement technique because of the multitude of possible adjustment. In addition, the nature of live music is different, not least because most of the higher dynamics of the music playback of sound recordings such as CDs, so, for example, the requirements for processed through the PA dynamic range are higher.