Public address

An electro-acoustic system ( ELA), and electrical loudspeaker system is a sound system and serves essentially the dissemination of information, especially the language. The applying systems are therefore optimized for comprehensibility and coverage and less on authenticity in sound, as is the case with PA systems, which are used in contrast to electro-acoustic equipment mainly for live and live performances. Modern ELA come but in terms of sound quality well within the range of PA systems.

Applications and Properties

Electroacoustic systems are used in airports, railway stations, public buildings, shopping centers and sports facilities. In the past, electro-acoustic equipment have been widely used in so-called local call systems.

In the GDR, it was common until the end of the 1980s, also equip enterprises and other public institutions with a high number of employees with ELA. The facilities were referred to as operating radio and should not be confused with the operation of radio in the modern sense.

The spectrum of applications ranges from a PA background music on pause gong to alert emergency maneuver.

To this end, these systems are built especially stable. It can be installed, which are automatically looped upon failure of a regular amplifier by using a pilot tone at the site for this purpose redundant amplifiers, so-called backup amplifier. Furthermore, with an emergency power supply or uninterruptible power supply (UPS ) is the system, if it must be operable in case of power failure, equipped. To further increase the reliability impedance monitoring can be used for each loudspeaker circuits, which can signal a change in the AC resistance, as occurs in disconnecting speakers or cable damage.

In practice, usually several loudspeaker circuits are set up. On the one hand, this allows specific announcements in certain parts of the building, for example, at stations for the individual platforms, on the other hand is a prerequisite in order to divide the required total output power of the system on several, then small-sized amplifiers, which in turn benefits the operational safety of the plant.

The operation of PA systems can, in contrast to PA systems usually done by laymen without how any technical background. The equipment for paging and music on hold, for example, have only a few settings such as volume and on / off. Further controls, Expertise is necessary for, are hidden behind a flap or housed in locked cabinets or rooms.

Operation

Electro-acoustic equipment have only one audio channel, so they work in mono. The originating from one or more stations or other sources sound signals are generally ( 0.7746 volt reference U0 =) in symmetrical form at the inputs of the ELA with an absolute level of 0 dBu.

Furthermore, control inputs for signaling (eg, break Gong ) and alerting (eg fire alarm) available. The audio signals thereof are generated by respective modules within the PA and fed to the amplifiers similarly to the voice and music signals, where appropriate, via a switching device.

Modern ELA transfer the digital audio signal via communication networks (LAN, WAN, ... ), where the speech is digitized directly at the station, and is converted back to analog signals just before the amplifier. In between, the data can be processed, for example, to reduce possibility of feedback digitally.

100 - volt technology

The outputs are in so-called 100 - volt technology. The output voltage of the amplifier is highly tensioned by means of a transformer up to 100 volts at maximum power in order to transfer them over relatively thin cables and long distances without appreciable loss can. It is also advantageous that you simply can group to an amplifier output very many speakers in parallel. Every single speaker has a transformer (transformer), the transformed down to 100 volts back to the voltage for low impedance systems. So you need to add only the respective retrieval performance of individual speakers in a system. For example, an amplifier with 120 watts of output power twenty speakers to six watts ( 20 x 6 = 120) or twenty speakers are connected to three watts and six speakers to ten watts ( 20 × 3 6 × 10 = 120). As a simple cable shielded wire cables are of the type Y ( St) Y 2x0, used 8.

Commercial radio in the GDR

By the end of the GDR, it was common to equip enterprises and other institutions with larger numbers of employees with so-called commercial radio. Which operates essentially corresponded to that of still widely used ELA and usually based on the 100 - volt technology. In this respect, the term mobile radio is somewhat misleading, because the transfer was wired, not wireless. The name derives rather from one for operations from imaginary radio program.

Operation of radio usually allowed two modes: compulsory and optional program. The reception of the platform could be influenced by the user of the compulsory program not.

The electoral program served i.d.R. of entertainment and general information of employees. These programs of public broadcasting were often fed in the operation of radio. In larger companies, there were also their own sound studio with professional studio equipment and some side by side or full-time editors who designed the programs of the operating Funke and is primarily dedicated internal issues. Thus, the operating radio added often the information and service functions of the operating newspapers. Most mixed operation took place, so that the mobile radio in the greater part of the time rendered a public radio program and only at certain times, for example, during breaks, their own contributions sent.

The compulsory program consisted i.d.R. only of announcements that should be available to all employees, such as Broadcasts, alerts, and emergency announcements. His reception could not be influenced by the users. Here, the word refers to the so-called duty circuit within the ELA and not to a possible duty of the employee to listen to the program. While a mandatory program was broadcast, the electoral program has automatically muted.

For the reception of the operating Funke's offices, rest rooms, corridors and factories were equipped with speakers. In some establishments speakers were set up in the grounds. The speakers in offices, break and other small spaces possessed the volume of the election program regulated or the electoral program could also be turned off via a volume control enables. On the volume of the compulsory program the controller had no effect. Speakers at which the reception of the election program was not useful (eg in rooms with poor acoustic conditions, workshops, outdoor facilities ), were frequently designed for the reception of the compulsory program and were therefore most of the time out of service.

To transfer the programs of private mobile radio were usually three - or multi-conductor cables. Here, each served a vein for the supply of the election and the mandatory program, and a wire as a common return line. In the speakers then a program artery using the volume control slider and a wire was connected directly to the transformer.

As an amplifier often came special operating radio amplifier in 100 - volt technology used. It further remote sub-amplifiers were operated in order to save transmission capacity in larger companies often. These amplifiers received the program via a 100 -volt line - that were almost like a speaker connected to a different amplifier. About a remote switching criterion a switching of the amplifier outputs could be effected. In this way, the distinction between compulsory and optional programs were implemented.