PA system
A PA system (also known as Public Address ) is a sound system that is used to reproduce speech or music to an audience . It is used wherever it is necessary to cover large areas with sound as evenly as possible.
The PA system is a branch of event technology , thus stage technology and sound technology .
term
In German usage, the term “PA” mainly refers to stage technology (English: Sound Reinforcement System ). Systems for the transmission of pure language information such as B. Local call systems are summarized under the term electroacoustic system , which comes closer to the original English meaning ("public address").
commitment
Because of the high cost of transport and setup, the PA is often provided by the organizer, especially for small to medium-sized performances or festivals, who can take care of the setup at the venue (if necessary several days in advance, if he does not have a stationary PA anyway - System ready (e.g. in discos). The dimensions and structure of the PA are then adapted to the requirements of the venue. For larger shows and on longer tours, however, the PA is usually transported from performance location to performance location. In some cases, several identical systems are used so that one can always be set up in parallel at the next venue.
The so-called backline connects to the PA system and is usually brought along by the performing artists themselves and tailored to their individual needs. In contrast to the PA, the backline can easily be swapped between the successive performances of several performers.
Components
speaker
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Since loudspeakers have different radiation characteristics depending on the frequency to be transmitted and sound is refracted differently depending on the frequency , PA systems are often divided into bass loudspeakers and mid / high-range loudspeakers. In addition, there is usually the option of adding a subwoofer .
Small PA systems, which are used for birthdays, weddings, lectures, bands and other musical purposes, are usually composed of one or two subwoofers and two to four mid-high speakers. Large PA systems that are used at concerts, theater performances or in discos and tent events are usually composed of at least four subwoofers and six mid-high speakers. In principle, the number of loudspeakers is open, so that 40 or more loudspeakers are often used at large concerts. On stages, the loudspeakers are often connected to each other to form towers and hung on trusses ("flown") using flight harnesses.
For larger events, six 18 "woofers (each with 1 kW) are often used in the bass range, as well as two double 21" woofers, which provide the deep bass.
In the meantime, however, it has become established to use so-called line arrays at major events , since better results can usually be achieved with these systems due to the performance differences between spherical and cylindrical shafts .
The two loudspeaker arrangements on the side of the stage are referred to as the left and right PA wing.
amplifier
Amplifiers in PA systems can usually generate an output of several kilowatts and have special requirements in terms of reliability. As a rule, several power amplifiers with high power are used, which mostly control the individual channels (mostly right / left, but also additional channels, for example a delay line ) and frequency ranges (low / mid / high range) separately. With active speakers, the amplifiers are built directly into the loudspeaker boxes.
cabling
The signal path starts on the stage with the instruments and the microphones provided: Here, mostly with XLR cables, the various signals are fed into a stage box and into a multicore leading to the mixer or - for smaller systems - directly via XLR cables Mixer headed. The XLR cables are usually connected symmetrically so that any radiation can cancel each other out. In addition to the stage signals, the signal sources mentioned above (CD recordings, etc.) are connected to the mixer (some with cinch cables); Variable gain amplifiers are mostly about Insert cables ( stereo - jack plug to two mono into the signal jack plug) looped .
The mixed signal reaches the output stages (via multicore / XLR), which ideally (due to the ohmic resistance of the cables) are located near the speakers or built into them. These are connected to the power amplifiers via loudspeaker Speakon , EP5, and earlier often also XLR cables (which, however, have to be wired differently than XLR microphone cables). For the connections between power amplifiers and loudspeakers, special sockets (regardless of which connector system) are used, which close a contact when the plug is inserted, without which operation of the power amplifier is prevented. In this way, damage to the output stage due to the self-induction of an open output transformer is avoided.
Modern public address systems transmit audio digitally via networks ( LAN , WAN ), whereby, for example, speech is digitized directly at the intercom and only converted back into analog signals before the amplifier. In between, the data pass through a digital signal processor (DSP) or parametric equalizer, for example .
particularities
In the case of live sound reinforcement, special attention is paid to the system's freedom from feedback .
As they often have to change location and generate high sound pressure levels, public address systems are designed differently from hi-fi systems. PA systems are more robust and heavier, as the loudspeaker housings must not resonate even at high volumes. At major events, workers, so-called roadies , are deployed for assembly / dismantling and loading (often also accompanying passengers) . In addition, PA systems are much more complicated to set up than hi-fi systems. That is why one or more specially trained sound engineers are responsible for the cabling and the soundcheck .
In order to reduce early reflections and reverberation in rooms, it is important to only cover the areas in which the audience is located. To be
- Running Time Delayed support speaker
- (mostly vertically oriented) loudspeaker arrays
- (mostly horizontally oriented) loudspeaker clusters
- Waveguides or horn speakers
used. With regard to the last point, it is important to pay attention to the Haas effect , trading as well as the term and level difference .
Furthermore, the maximum achievable sound level (which is why loudspeakers with a higher degree of efficiency , e.g. horn loudspeakers , are used in the PA sector ), operational safety even with permanent overload, handling during assembly and dismantling (robustness, rounded corners) are of decisive importance.
Although the requirements differ from those of a hi-fi system, some PA systems definitely achieve the playback quality of hi-fi or studio systems (especially PA systems for operas, concert halls and movie theaters). Due to the large number of possible settings, the overall sound of a PA system is not inconsiderably dependent on the skills of the operator and the measurement technology used. In addition, the character of live music differs from the music reproduction of sound carriers such as CDs , not least because of the mostly higher dynamics . B. the demands on the dynamic range that can be processed by the PA are higher.
control
The PA system is usually controlled via a mixer that is connected to the power amplifiers. The mixer forms the preamplifier and, in addition to microphone and instrument inputs, usually also has connections for e.g. B. CD players or other playback devices as well as connections for effect devices , control amplifiers and equalizers , all of which have the task of changing the music and language so that the desired sound is achieved. Most of these devices are manufactured in 19-inch units, which can then be screwed into the racks provided for them (e.g. the siderack ). The mixer and the technology connected to it are usually housed in the Front of House (FoH) so that the sound engineer can prepare the performance where the audience hears it.
Monitoring
In addition to a PA system, there are usually monitor speakers at music events. It enables the artists on stage to hear their own voices and instruments better, as the sound direction of the PA usually points away from the stage and therefore only a dull sound or delayed reflections from the rear wall of the hall or distant buildings on the stage without monitoring can be heard. With a distance of the reflection walls of only 50 m, the sound waves need almost 1/3 of a second to go there and back.
Monitor systems are particularly required for live music, since the drums in particular make it almost impossible for a singer without his own sound system to hit the notes correctly if he cannot hear himself. The stage loudspeakers give the performers a hearing impression that is similar to that of the audience and can thus better coordinate the interaction.
The monitoring can be realized by loudspeakers directed towards the stage or by earphones ( in-ear monitoring ). The latter is used more and more frequently with increasing development to reduce costs in radio technology, since it can significantly reduce feedback problems.
In-ear monitoring can also benefit the sound in the direction of the listener, since the sound on stage can be significantly quieter and no longer mixes so strongly with the PA sound directed towards the audience. This can result in a much clearer sound, especially in reverberant and small rooms.
literature
- Rolf Beckmann: Manual of PA technology. Basics - Components - Practice. Elektor-Verlag, Aachen, 9th edition 2000, ISBN 3-921608-66-X .
- Fritz Kühne: Music transmission systems, planning, construction and maintenance. 5th edition. Franzis Verlag, Munich 1968.
- Siegfried Wirsum: Practical sound technology, device concepts, installation, optimization. 1st edition. Franzis Verlag, Munich 1991, ISBN 3-7723-5862-4 .
- Michael Ebner: manual of PA technology. 1st edition, Elektor-Verlag, Aachen 2002, ISBN 3-89576-114-1 .
